Cable vendor slapped for unproven claims The Advertising Standards Authority has slapped hi-kit supplier Russ Andrews for claiming its super-duper mains cables could reduce radio interference on the power line. According to the the company, its PowerKords reduce noise in the mains supply because they are wrapped up in woven conductors, enabling the company to charge …
I had this conversation a few years ago. It took an age to explain to him that your electricity travels down:
5 miles from the substation in underground cables, probably over 20 years old, to your meter. (Also, connected to everyone else in the vacinity including businesses)
10m or so of the cheapest Mains cable your contractor thaught they could get away with. (BS 7671 compliant if your lucky, but you cant count on it)
5 feet of power cable.
Besides, if your amplifier is so rubbish that it cant properly reject RFI on the Mains, you should seriously consider spending the £1200 on getting another amplifier, so even anything amps you could get for that amount should be able to do that.
The mark-up on cables is already too high, especially with these special "digital" cables and the fact that so many people are miss-sold products is disturbing.
Those that spend £1250 on a mains cable should consider carefully their contribution to the world at large. How could that money have been better spent? Could they have saved someone's life with that money? Could they have improved someone's situation with that money? Was the feeling of possibly eliminating some possible interference so significant that it actually outweighed the well-being and satisfaction of doing something for someone else.
Also, half of these self-proclaimed audio files would have more benefits from changing their room acoustics than just through buying a glorified kettle lead.
I'd enjoy listening to their before / after spiel as they tried to justify spending 1200 quid on a kettle lead...
The bull would be phenomenal because lets face it they would have to convince you (as well as themselves) that they *could* hear a difference in order to justify to themselves it was money well spent.
Psychics etc can advertise all they want, as long as they can prove what they say in the advert is true. That is usually the point where they fall down, which is why most advertising merely consists of "I'm here" type stuff. Mind you ... Just google ASA Sister Charlotte for the media frenzy that happened when *I* forwarded the ASA a psychic's leaflet. (Anon because I don't want her knowing where to send the curses... lol..)
...more likely to be an IEC power lead - a kettle lead has a slightly different connector on the end.
And, I imagine the Russ Andrews would be charging £2k for one of those - due to its high power handling in extreme environments!
Mines the one with the bag full of snake oil in the pocket.
The only real difference in your water boiler is the notch at the end stopping you plug a PC one into a kettle (and the fuse and cable ratings).
I work with people that plug in those connectors daily and half of them give blank looks when you say an IEC connector.
I've got one of these, with a clear plastic sheathing so you can see the braids. It came "free" with a power supply I bought a few years ago. I thought they'd done it because it looks neat.
You know, this might well be the very thing that pushes me into setting up an eBay account. Anyone wanna buy a grand's worth of braided cable...?
If he'd only charged a moderately extortionate sum like £100 -
a) he'd have flogged more of these cables-of-dubious-benefit
b) his disingenuous advertising probably would not have been investigated.
Can't believe people belived it in the first instance. Spend £1000 on a lead that is then plugged into a £3 socket connected to yards of 30-year-old twin-and-earth copper mains.
You see, most people would not spend even £100 on a kettle lead, regardless of whether we believed the claims or not.
However, people with too much money (like celebs, heiresses, people who spend vast sums on "art", especially where the artist is still alive) would also not spend £100 on a kettle lead because it is both too expensive and not expensive enough. But you tell them it is worth £1200 then they believe that firstly it must be good, and secondly that their other heiress friends will laugh at them if they haven't spent £1200 on a kettle lead. The kind of people who would buy these things are not going to be financially troubled by wasting a few thousand quid every time they buy a new stereo.
You can also guarantee that the people who complained about the add would never spend £1200 on said cable, even if it was conclusively proved to give sound quality guaranteed to induce orgasm in listeners in under 30 seconds. Similarly those who would have bought one before would not be dissuaded by the ASA rulings. Just look at the MMR jab, New Coke, Homeopathy, psychics and the X-Factor viewing figures as examples.
When can we expect a similar judgement for the guys who charge £1500 for 'Ultra-High Quality' HDMI cables. Ignoring the fact that there is no difference between HDMI cables, I've seen several both online and in stores that claim that they contain some revolutionary new technology that prevents the image data from degrading on it's trip to the TV.
"Ignoring the fact that there is no difference between HDMI cables,"
Can you substantiate that?.......whilst I haven't tried any super-duper HDMI cables, there is a clear and noticeable difference (picture wise) between those cheap HDMI cables that are supplied with some equipment and other cables from specialist brands, such as QED.
It should also be noted that there are many experienced professional reviewers who also notice the difference, UNLESS you are implying that said personnel are in the pocket of certain brands or that they are encouraged to give such reviews to products due to that brands advertising spend....
In the end, it's down to the buyer - if they can see a difference, then it's up to them to justify whatever the price is....
I've had a cheap HDMI cable cause picture distortions. (corruptions NOT qualitative differences)
My theory is that the metal wiring was too thin, too impure and so too resistive to always let the signal be meet the threshold to be detected. I think crosstalk from adjacent wires might have been responsible.
Whilst I agree with all the comments about digital/checksums/etc, it must still be noted that the signal is ultimately analogue, and so can be rendered intermittent, at least, by some effect.
Given that usually logic will require a <20% voltage range to register low, and >80% the voltage range to register high, I can see how resistance combined with crosstalk could lead to a certain wavering of the attained peak voltage for a high, but am not sure about lows.
The problem here being LVDS, I presume the issue would manifest in a more complicated manner - but ultimately result in voltage differences that wavered on the detection threshold.
Alternatively, if the wire quality wasn't consistent for the clock and data lines, there could be a phase shift that would cause data loss - perhaps triggered by some capacitive effect? *
All I know, is that though I have NOT seen a -qualitative- difference, but I -have- seen a signal come through so variably as to cause the odd few pixels or lines to be dropped/corrupted in each frame - with the remainder screen area being received perfectly.
(And I thought any effect was impossible until I saw it - and then took the duff cable to work so a colleague could be equally surprised!)
* I'm not an electronics guy, but write device drivers and use an oscilloscope to check/verify signals on dodgy new hardware enough to have acquired a few ideas.
HDMI cables are like network cables. Cat5 and Cat5e are different. As is Cat6. What is the difference? Bandwidth (the MHz frequency range the cable can handle). Other differences include wire twist methods, conductor quality, and end termination. All of these components help determine what standard the cable can be rated for. Cat5 quality and twist prevents it from handling Gigabit frequencies properly, and likely your NIC will limit you to 100Mbit. The frequency (bandwidth) range required exceeds the cable's ability. HDMI cables have similar issues, where they're rated for HDMI 1.3b, 1.4a, etc. Granted, you can get a cable that, based on that hard-kink you put in it to sit your TV or Blu-Ray flush to the wall, will compromise the cable's already-mediocre build and cause it to down-grade the signal to the point of only being able to pass 720p. Cable length is important also, since 1080p frequencies across a poor-quality cable will likely require a shorter length, just like Cat5e is not recommended for longer than 100 meter runs (even though it may actually work "well" for 150m in your situtation, lucky you).
With all this in mind, if you're buying a 6ft HDMI cable, likely ANY cable you get will run at it's RATED spec (1.3b cables have no hope of running 3D Blu-Ray, for instance. That's what 1.4 cables are for), unless your cable is defective (or you broke it). Defective rates or User Error is outside the scope of this retort.
So, for those that missed the point, here's a summary:
HDMI is a digital spec. It will auto-negotiate the best quality the cable can handle in the given situation. If you or your cable is a numpty, you may only get 720p when you were hoping for 3D Blu-Ray. Read the cable's spec. Most are likely 1.3b, which can handle 1080p, but not 3D Blu-Ray. No, your HDMI cable from 1.1 days won't handle 1080p.
The "it's digital" people don't acknowledge the auto-negotiate side of the equation, which is what the "high-quality cable is important" crowd is likely seeing.
"(1.3b cables have no hope of running 3D Blu-Ray, for instance. That's what 1.4 cables are for)"
Absolute, complete and utter cobblers.
This comment shows you have little understanding of the difference between the varying HDMI definitions, or that there is no such thing as a "1.3b cable" or a "1.4 cable". Referring to a cable as "1.3b" or "1.4" [compliant] is *utterly* meaningless, and is just marketing hog-wash/bullshit.
There is NO difference whatsoever between a HDMI "1.3" and HDMI "1.4" cable, in fact you should never see HDMI cables defined in this way, for good reason. ALL HDMI compliant cables from the very inception of the HDMI standard - from back in 2002/2003 until today - are, by definition, considered to be HDMI 1.4 compliant (and HDMI 1.3, 1.2 and 1.0). And that includes the cheap cable you get bundled with every HDMI device, and any and every HDMI cable you may already own.
There are only four official HDMI cable types, defined as follows: Standard Speed, High Speed, Standard Speed with Ethernet and High Speed with Ethernet. Ignore any mention of "1.3b" or "1.4" in relation to HDMI cables, as it doesn't mean a thing and would only be used by someone who doesn't understand the nature of the product being discussed.
Your "1.3b cable" may actually qualify as a High Speed cable in which case it should display 3D Blu-Ray from a HDMI 1.4 source without any problem. Equally, your "1.3b cable" could rate only as a Standard Speed cable in which case it would not have any hope of displaying 3D Blu-Ray (and may even struggle to pass regular 1080p). The point being, HDMI cables are not categorised by the "version" of the HDMI specification, merely their bandwidth carrying capacity - a cable is either a Standard Speed cable or a High Speed cable, not "1.3b" or "1.4".
And this is where the construction of the cable becomes important, as good quality cables will, on the whole, be able to carry higher bandwidth signals than less well made alternatives.
High Speed cables were introduced to support the new features added by HDMI 1.3 (deep colour etc.), but their physical construction remained unchanged from HDMI 1.1, the only difference being better quality conductors, insulation, construction and connectors, all of which which combine to allow for higher bandwidth signalling.
The only physical modification to the construction of HDMI cables occurred with the introduction of the "with Ethernet" optional feature ushered in by HDMI 1.4.
"with Ethernet" uses previously unused conductors that are now converted into a twisted pair so if you want "with Ethernet" then you'll need new "with Ethernet" HDMI cables, but if not then your current High Speed cable will be fine. You'll only be buying a "with Ethernet" cable if it says "with Ethernet" - if it only says "HDMI 1.4", give it a wide berth as for all you know it might be a Standard Speed cable.
If you have purchased good quality "HDMI 1.3b" cables that have plenty of headroom for future bandwidth upgrades, then these cables most likely fall into the category of "High Speed" and you will be in good shape to watch your 3D 1080p Blu-Ray video(s) from a HDMI 1.4 source.
As for differences in HDMI cables in general, well yes of course they do exist - a well constructed cable will successfully carry a high bandwidth signal over a longer length of cable than an inferior alternative (eg. at 100 feet, 1080p may be possible with a good cable while only 720p is possible with a less well constructed alternative).
However for short runs it's very, very unlikely that there will be a noticeable difference unless one of the cables is spectacularly bad verging on defective - either the cables will work, or they won't.
As stated a cable either meets the Cat5 and Cat6 standard or it doesn't, but I have come across shops selling "high quality" cat5 or cat6 cables for home entertainment purposes. Apparently if you wire your home entertainment network with these you'll get better sound and picture (yeah, right). Of course this misses the point that most people run this stuff over wireless. How long before these dodgy shops start selling "special" wireless antennae for home entertainment use?
"UNLESS you are implying that said personnel are in the pocket of certain brands or that they are encouraged to give such reviews to products due to that brands advertising spend...."
I don't think that needs to be implied, it can be taken as read. HDMI is a digital standard and as such the quality can be very easily measured. eg does the pixel at point x,y have the same RGB value with this cable and that cable? Are there any errors reported from the deserialiser? What does the eye diagram look like?
Then people will claim 'oh but what about jitter?', but its digital video so pixel x,y always goes to the same place and the pixels always come down the wire in the same order.
Of course no-one would do these tests as it would show up their cables. Expect these guys:
http://www.bluejeanscable.com/articles/belden-hdmi-update.htm
Does thereg look better if you use a more expensive DVI-D cable?
as good ol joules watt was fond of pointing out in the wireless world...
digital signal... aint no such beast in the real world
your 0 and 1 are represented as voltages with asscociated currents dependent on various impedances. And those impedances will have different effects on the various (odd No.) harmonics making up your 0 & 1 signal, softening an edge here, overshooting there. And as such are subject to the same laws of phsysics as an analog signal in a 'analog' cable.
that said 'audiophile quality' anything is ALWAYS bollocks.
these people are morons and deserve nothing but our scorn.
It's quite simple, HDMI is a digital interface. In fact, if you are using a commercial Blu-ray disk, most likely it's an encrypted digital link. Either the TV can recover the digital signal or it can't, and any faults will be obvious ones in picture break-up. Indeed, if the encrypted signal was not arried perfectly (with any built-in error correction), the signal would not be recoverable at all.
Of course there are advantages to higher quality cables, like robustness. However, as long as it meets the appropriate HDMI standard for the resoution in question (skew, attentuation, cross-talk etc.), it will either work, or it won't. Higher quality cables may be capable of longer runs, but they won't improve picture quality.
http://www.hdmicablecomparison.net/hdmi-cable-quality-comparison/
Note the above does not, of course, apply to SCART or other analogue cables.
Human beings have a wonderful ability to convince themselves that they are seeing a difference which doesn't exist, even if it is technically not possible. It is generally related to the amount of money that they've just spent, and it's a charactestic exploited ruthlessly by vendors.
>there is a clear and noticeable difference (picture wise) between those cheap HDMI
>cables that are supplied with some equipment and other cables from specialist
>brands, such as QED
The nice thing about your post being anonymous is that I can explain what a complete idiot you are without needing to worry about pesky libel laws. Note I'm prepared to use my real name here.
You seem to be unaware that HDMI uses a digital signal. There is no degradation of signal because of cable quality, it simply arrives correctly, or incorrectly.
So, unless the cable is of such poor quality that it cannot transmit a simple digital signal without error, the signal you receive will either be correct (ie it will show the picture), or it will be incorrect (ie it will show corruption or nothing).
You won't get sharper skin tones, richer sounds or a more realistic plot in your movie just by using a cable that's fifty times the price. All you'll do is make some guy a little wealthier, at your expense.
>UNLESS you are implying that said personnel are in the pocket of certain brands
>or that they are encouraged to give such reviews to products due to that brands
>advertising spend
Corruption in the publishing world? Oh, that would never happen!
No, more likely they're just gullible people like you who are convinced they can notice a difference where there is none.
It's not rocket science. To test a digital cable for quality, you compare the source input with the destination output. Run a checksum on them, if they're the same, the cable is OK. If not, throw it out. That is the ONLY way to review a digital cable.
If you're reviewing a digital cable by letting "experienced professional reviewers" watch the video and making a subjective decision about which cable is best, you're doing it so fucking wrong that the only possible explanations are either financial reward or complete ignorance.
In any case, I think you're on the wrong website. This is a technology website.
HDMI is a multi-lane low voltage differential serial digital protocol with forward error connection (like PCI express or SATA). It'll either work perfectly unless the cable is so crap or broken that it doesn't.
"It should also be noted that there are many experienced professional reviewers who also notice the difference, UNLESS you are implying that said personnel are in the pocket of certain brands..." Yes that would certainly appear to be the case.
"there is a clear and noticeable difference (picture wise) between those cheap HDMI cables that are supplied with some equipment and other cables from specialist brands, such as QED."
No, there isn't. There can't be. It's an error-corrected digital signal, it either gets there & gives you a 100% picture, or it doesn't get there and gives you no picture. Any differerence that you imagine you're seeing is entirely due to your subconscious desire to believe that you got something for whatever ridiculous amount of money you spent on it.
Some have commented that as the HDMI signal is digital that perhaps all HDMI cables act the same and hence you either get a signal or you get a corruption of data (which may or may not be resolved by corrective action from the 2 pieces of hardware that are being connected together).
There is evidence to support the fact that:
1) Most HDMI cables are different to each other and hence although they all pass the relevant HDMI specification, it is likely that some will work better than others, with less losses in the cable, due to the materials used (both for conductors and insulation) and the way in which the cable is constructed.
2) Even if a signal is digital it is still subject to the resistance, capacitance and inductance of the cable itself, as well as how the internal conductors are "wound", which is perhaps why some cables work over short lengths, but the exact same cable, in a longer length doesn't work ...
http://www.audioholics.com/education/cables/long-hdmi-cable-bench-tests/hdmi-cable-testing-results
I would therefore humbly submit that a case can be made for the fact that different HDMI cables can and will affect the signal flowing through them......and hence this can affect the signal received at the "sink" end.
I'll get me coat now......and go back to living under the stone over there >>>>
> likely that some will work better than others,
The physical construction of the cable will certainly affect the signal passing along it, that's basic physics. The point about HDMI being digital with error correction is that any such signal damage is binary: either the signal gets through, and the picture is all correct, or the signal doesn't get though and there's no picture. What CANNOT happen is for the picture to be in some way 'poor' or 'less clear' or 'lower quality' with poorer cables, digital signals simply don't work that way. If you have a picture with a given cable, then you have the best picture you're going to get, and no other cable can make it better no matter how much you pay.
> perhaps why some cables work over short lengths, but the exact same cable, in a longer length doesn't work
No, that's explained by transmission theory. In any cable, different frequencies suffer different delays, and different losses. For analogue signals that will cause loss of picture detail as the cable gets longer, since the high frequencies carry the picture detail and they get attenuated proportionately more as the distance increases. For digital signals the effect of that is to "smear out" the nice square pulses, rounding their corners, until they all run into one another. At the point where you can't distinguish two pulses, you lose your signal. It's often referred to as the "digital cliff", everything is perfect until you suddenly "drop off the edge" and vanish.
It is not true that all hdmi cables are equal, but the thing is that while you can certainly get a rotten signal (drops or no sync at all), once you get a "good" signal you cannot get a "better" signal.
Even a mediocre signal will be "good enough" and hence give the maximum performance due to applied forward error correction. What's more, "the digital" and the FEC effectively hide cable quality so you can't know how good the signal really is beyond "good".
The only leeway would be, once the signal got decoded upon arrival, whether needing to apply the FEC decoder would cause delays in the signal which might somehow be subconciously perceptible or whatnot. <tin-foil-hat>Carefully modulating the errors to trigger the FEC decoder might even carry subliminal messages.</> But somehow I find that a bit unlikely. But hey, maybe you can build it and sell it to the government.
>> I would therefore humbly submit that a case can be made for the fact that different HDMI cables can and will affect the signal flowing through them......and hence this can affect the signal received at the "sink" end.
Yes, but as pointed out above, this is digital not analogue and you clearly don't know the difference. Corrupting the digital signal will create errors, not degrade the quality of the image, but create errors in the bitstream. The result is highly visible "blocking" of the picture - not a degradation of quality.
If you aren't getting this blocking then the cable is good enough - and no amount of improvement in it's quality will have any effect on the picture or sound.
Yes, as already said by other, a cheap cable may in fact not work over longer distances that a better cable would. But for a given cable, when you plug it in it will either work - or it won't. If it's marginal then there will be a picture but with blocking at random intervals - which means it's not working. it won't (for example) make the picture fuzzy, or add snow, or any of the analogue effects that these high quality cables are claimed to avoid.
that there is some good common sense behind the idea of making, what is essentially a shielded mains cable. By preventing the cable acting as a "receiving aerial" for most if not all RF signals, then this could be a good idea - esp if those signals are produced locally (ie wireless routers, mobile and cordless phones, laptops etc).
But of course there would be lots of RF on the mains already, picked up from before the mains entered the consumers house, so just shielding a cable won't stop that.....
So, for over a grand I could get a very good quality UPS/mains filtering system, and install that just for the ring where the audio system is connected to, which would do a far better job IMHO.
Real Audiophiles would not have any equipment that could possibly suffer from any form of noise on the mains, so why would they buy one or more of these cables?
If you've got equipment that is suscptible to mains interference then you are either not a real audiophile or you would replace the equipment.
These cables are not aimed at audiophiles, they are aimed at gullible suckers.
... that you'd need that spendy cable not to the wall socket, but down to, oh, the block transformer at least, more likely all the way back to the generator plant, for simple shielding to work. Do audiophools really not think farther than the nearest wall socket? Wait, don't answer that.
Other than that, it goeth well with the only half as spendy ethernet cable with a "directional arrow" on it. Though the thought that some people actually spend money and effort on this is a bit appalling, it made me laugh. And anyhow, people's own money is theirs to do with as they please.
People spending other people's money like it's free (hello labour) is something else entirely again. I think more politicians need a hobby to go with a honest job instead of the arduous existence of being a politician, justified only by fudging expences. Say, dear MPs, I heard this beautifully fancy audio rig lately, why don't you pop over and have a listen?
I've often thought that companies like EDF are missing a chance to make money here. If people are willing to spend £1000 on the last metre of cable from their wall socket, how much more would they pay for a fully-screened gold-plated oxygen-free directional litz-wound cable all the way to the local substation? Fuelled with green electricity as well.
PT Barnum underestimated things.
A shielded mains cable actually makes sense in some circumstances, and they are available and fit for purpose. They cost a small margin more than conventional mains cables. That is, for a few pounds.
In addition to the sin of selling grossly overpriced snake oil (hardly a new new thing in audio) these guys commit an even greater sin. They clearly have so little actual understanding of what they are doing or selling that they were unable to construct a test that would have shown a difference. It isn't all that hard. (That is, they could have shown that shielding is helpful, not that a thousand quid of shielding helps any more than a few tens of pence.) But they have clearly demonstrated an almost total lack of understanding of physics with what amounts to an own goal. Priceless.
I was once berated by a housemate, who had professional monitor speakers attached to his computer (douche used them to play Rush at 1000 decibels - nothing wrong with Rush of course) for using an EQ to make my music more pleasent to the ear. I belive the phrase "I want to hear the music as they intended it to be heard, as it sounded in the recording studio" came up at one point.
He listened to 128K MP3s.......
He would be one of these people that buy this kind of cable.
And would deserve it.
"Mains supplies are one area that can reportedly make a difference"
Unless your mains supply is grossly deficient (maybe a generator) and falls outside normal tolerances, this is junk. It's the job of the power supply in the audio equipment to provide appropriately regulated outputs to the audio components (and all the power interconnects etc.). This, including appropriate shielding and filteringwhich should eliminate the effect of any normal power supply variations to the audio equipment or any mains-borne RFI. Designing high-quality power supplies is hardly rocket science, and a decent one will withstand pretty well anything a normal mains supply can throw at it (which also means those mains conditioners are a waste of money too if your audio kit is designed properly).
Of course if the Audio kit isn't properly shielded from interference, then that's another problem but still comes down to proper design.
Putting a mobile phone next to analogue hi-fi kit isn't a bad way of dining out if the shielding has been done properly (and associated external signal cabling). If you don't get breakthrough from that, it's probably pretty well shielded.
When I read articles like this, it is a hard decision as to whether or not to post the URL that follows.
If I don't post it, people with clue may miss out on some 'interesting' entertainment.
If I do post it, a charlatan may make some additional money out of gullible people.
So on the whole I post it occasionally, and at the moment it's almost a year since last time.
www.belt.demon.co.uk
Enjoy.
Thats quite something. I cant work out if its a tongue-in-cheek satire, pointing out the meaninglessness of many audiophile improvements or genuine content. In any case, its quite funny.
Personal fav in the 'free sound improving techniques' section:
Plain piece of Blue paper under any vase of flowers or any pot plant in the listening room.
If you have a vase of flowers or a pot in a plant pot in the listening room, stand the vase or the plant pot on a plain piece of BLUE paper. Listen to some music for a short time, then remove the piece of Blue paper and see if you can listen to the same music with the same pleasure - without the piece of Blue paper in position !!
This is truely groundbreaking stuff.
(Mines the one on the blue piece of paper, with a single corner pinned back)
I'm no electrical engineer but I have heard demos by a highly-regarded British hi-fi manufacturer in which changing the power supply arrangement to the source (in this case a CD player) made a hell of a difference to the sound. It's part of the upgrade path for their components, eg, adding an off-board power supply to your CD player so the on-board one handles the digital stuff while the off-board one handles the analogue. That can really work but, I agree, most of what this particular vendor sells must be hogwash -- and it gets a lot crazier than mains cables.
"adding an off-board power supply to your CD player so the on-board one handles the digital stuff while the off-board one handles the analogue."
That's not audiophile level stuff simply because a real audiophile would not have a CD player with a built in DAC. So the output from the CD player would be digital and the DAC would be entirely seperate including its power supply.
Interesting and related fact just to add to the fun...
When swapping the live and neutral (by turning a figure of eight mains lead 180 degrees) feed into a CD player back in the 90s, there was a measurable (read "oscilloscope") difference in the sound produced. Entirely subjective as to which was 'best'.
And, more importantly, it passed the "mum noticed a difference" test.
Discuss.
...
btw. These expensive kettle leads are usually plugged into a filtered supply (see the websites for that 'bargain' offering). It's still daft and subjective.
I'd rather spend the money on:
a) regular ear cleaning service (I'm sure *someone* does that?!?)
b) A better acoustically prepared room
That one is too easy.
There is leakage between the mains input and the signal output (there's almost always some, but in good kit it's negligible). The leakage is not identical between live and neutral (again nearly inevitable). The mains is rarely pure 50Hz or whatever those foreigners have. And the mains is usually near-0V on one conductor and live on the other.
If you're lucky the live is the one with the least leakage and there's nothing to see on the output. Leakage from neutral doesn't usually matter much because there isn't usually much signal to leak (neutral is usually earther somewhere either on the premises or not too far away).
Turn the power input connector round so there's a serious signal on the former neutral conductor and you may suddenly find there's enough signal leaking through the equipment to be detectable on the output(s).
I know this because I had a Grundig 1970s radio that sounded much better when the mains was plugged in the wrong way round, and I looked into it.
[yes different countries may have different electrical systems]
...the weak-minded fail to consider that the electricity doesn't originate at the outlet.
Using their "logic", one should be prepared to tear the house apart to rewire everything back to the local power plant.
They're idiots. And they bring down the average for idiots in general.
If we're being pedantic over not calling it a kettle lead, at least get it right. The IEC is a standards body, so an IEC lead could describe any of the standard connectors they define. Really it should be called a C13 lead as that is the connector on the end - the assumption being the other end has a country-specific plug on it. A kettle lead has a C15 connector on it for comparison.
As an ex-coworker of mine doug self says:
"Cables are directional, and pass audio better in one direction than the other.
Audio signals are AC. Cables cannot be directional any more than 2 + 2 can equal 5. Anyone prepared to believe this nonsense won't be capable of designing amplifiers, so there seems no point in further comment"
For a proper debunking of audio myths see his web article here:
http://www.douglas-self.com/ampins/pseudo/subjectv.htm
Bear in mind he's a pro-audio designer rather than just a random bloke off the street.
but what you perhaps do not realise is the the majority of home audio signals, at both line level and speaker output level are in fact unbalanced - that is one conductor is used for the signal itself and the other provides the earth. Even the negative terminal of say a solid state amplifiers speaker output terminal is usually at ground potential (ie house earth and assuming it is non-inverting).
(Recording studios usually use balanced XLR connections between equipments).
So, one could argue that the signal "flow" from sending to receiving device is dependant on that one conductor - and given that metals used for most audio cables are crystalline, so it is entirely possible that when the cable is drawn, that the crystalline structure could provide a different electrical characteristic with a voltage flowing in one direction, compared to the same signal flowing in the opposite direction.
Just my 2 cents worth.
> Recording studios usually use balanced XLR connections between equipments
Why do you think that is?
> So, one could argue that the signal "flow" from sending to receiving device is
> dependant on that one conductor
Well, I couldn't argue that. Not with a straight face, at any rate.
> so it is entirely possible that when the cable is drawn, that the crystalline
> structure could provide a different electrical characteristic with a voltage
> flowing in one direction, compared to the same signal flowing in the opposite direction
Just suppose, for a moment, that you were correct[1].
What effect would that have on the sound? Remember that this is AC, just as the post title says: current must flow in both directions for the signal to be transferred.
*If* your proposition above were correct, what you'd actually have is a source of distortion[2]. It would not lead to any directionality of the cable.
Vic.
[1] You're not.
[2] An op-amp with a diode in the feedback path makes for a very pleasant-sounding guitar distortion box. Unfortunately, it also makes for a rather good AM radio:-(
It's irrelevant whether one side of the loudspeaker feed is earthed or not as far as current flow goes. It's still AC. That's because the potential of the active side transitions from negative to positive and back again and the current direction reverses in both cables and essentially averages out to zero (assuming that the amp isn't so badly designed it puts a DC bias on the output). In any case, if the resistance of a cable varied according to direction of the current flow, it would be easily measurable. I've never seen the slightest evidence of actual measurements demonstrating that. It's simply hokum and yet another myth spread around by audiophiles.
Now to take the other point about differential drives, which is what XLR cables are used for. There are two main reasons for using differential outputs. The first is for noise rejection. The use of balanced wires means that the interference largely cancels out. Differential outputs are used on many systems where noise immunity is important. The second main reason is that on the output side a differential output allows for a much higher voltage swing between the terminals. For a given DC supply the peak-to-peak maximum achievable is doubled, which means four times the power can be delivered. Maybe not too much of an issue with mains powered equipment, but useful if you have an amplifier powered from a 12V DC system. Of course you also get noise rejection, but that really isn't an issue on driving high-powered passive speakers in anywhere but the worst environments.
So whether one signal is grounded or not, the current flow is still AC. Directional cables are so much junk science - if they were directional it would be measurable. Full stop.
(In fact you will find some XLR cables do carry a small DC current. That's because some3 condenser microphones requite a "ghost" power feed which means that there is a net current flow in one direction, albeit generally tiny. Needless to say it has precisely zero effect on the quality of the audio.)
a "direction of flow" indicator is only relavent on Analogue Hi-Fi Cables.
i spent £400+ on OFC Isoda Interconnect cables back in the late 80's and having a cable the wrong way round was actually noticable on some soundtracks.
(i had just spent £5k+ on a low end hi-fi system at the time, each module was £1K+ each)
these days HDMI and other digital cables is a waste of money as its either 1/0 in signal going down the cable, its irrelavent if there are 5 strands or 200 strands on the core conductor or wether its made of copper or lead.
these days its a waste of money to spend more than a few quid on an audio cable as all the music (thats not direct off a Vynal or CD) is of such low quality that just changing a cable isnt going to make any difference, crap in crap out!
you could use a PA speaker and you wouldnt notice the difference from an apple music download.
> a "direction of flow" indicator is only relavent on Analogue Hi-Fi Cables.
No, it is only relevant to the bank balances of those that buy and sell such cables.
Audio cable is simply not directional. Read any text on transmission line theory for substantiation.
Vic.
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Would anybody buy a mains cable at that price? And if anybody did then they are beyond help.
Even if sheathing the conductors did have a beneficial effect there is absolutely no reason it should cost more than a few quid.
Reminds me of the guy selling guitar leads with brass plugs a few years ago. He was selling them at vastly inflated prices on the totally spurious grounds that they would produce a warmer tone than leads with chrome plugs. I met some idiots who bought those and claimed they worked.
I presume the brainless idiot who was the first to downvote frank's question re single core vs multicore speaker cable doesn't know what "skin effect" is, and why it might be important for speaker cables.
School physics: skin effect is the name for the effect which makes alternating current in a conductor tend to be heavier nearer the surface. The effect increases with the (square root of) the frequency. At 50Hz the skin depth in copper is 10mm or so. Make that 5kHz (frequency 100 times higher, square root of 100 = 10, remember) and it's 1mm or so.
At 20kHz (just about inaudible) the skin depth is 0.5mm or so which means if the cable is standard solid core mains stuff, the highest audible frequencies are ignoring all but the outer parts of the cable, which means that for these frequencies the effective resistance ("impedance") of the cable is rather larger than might be expected based on cable dimensions alone.
Multicore cables (such as Litz wire - a generic term not a trademark) are designed to avoid "skin effect" issues, which is why you see them in radio aerials, and sometimes in speaker cables.
Still, why let basic physics disturb a good downvote, eh?
Litz cables are multi-strand cables *with individually insulated strands*. Their skin effect is negligible even at RF .
Ordinary multistrand cables, where the strands are uninsulated and therefore conductively touching each other, behave electrically like solid cables. There's a factor of 0.9 or so due to the fact that the cables don't completely fill the occupied space, but any skin effect differences between solid and uninsulated multi-strand cables will be minimal.
As to the likelihood of skin effect making a difference at audio frequencies anyway, a 0.5mm skin depth means that a cable needs to be more than 1mm diameter before a 20kHz signal would be affected. That's roughly 18AWG, which has a resistance of about 0.02 Ohms/metre (and is rated at 13Amps). With cable like that, you'd need a very big living room to get any significant difference in frequency response due to skin effect, or one hell of a powerful sound system if you'd need thicker cables where 0.5mm skin depth would matter.
I'm fine with basic physics, but I stick with my downvote.
I did a few years ago just prior to Part P and it gave me the benefit of extra outlets as well. I do have a Belkin PF50 protecting my setup and desktop PC but that's probabloy overkill as is.
Paris ? It needs her intelligence to accept the marketing and pay a grand for a kettle lead..
p.s. I not a trained sparky either although I did get one to do a check.
I don't generally post anonymously on this forum, but I'm going to this time because I'm going to get flamed. But I'm an engineer and an audiophile and this has to be done.
As someone famous once remarked, the most encouraging sound to be heard in a laboratory is not "Eureka", but "Oh. Errr. I wonder....". It's the spirit of enquiry, which most here seem to have forgotten.
If I take you back 20 years, some of you may remember the great analogue/digital audio flame war. The subjectivists said "Vinyl sounds better. We don't know why CD sounds crap, but it does". The vastly intelligent expert engineers said "Don't be stupid, it's 1s and 0s, if you read them off disk with no errors then it's perfect; the frequency response and the THD measure perfectly, you're imagining things, you're all idiots". Well, the digital-is-crap brigade didn't go away, and eventually someone with a foot in both camps started making some measurements to look for the difference between "better" and "worse" digital sources. And they found it - jitter. All but the most diehard digital clown now accepts that recovering and preserving a decent clock is actually quite hard, and the phase noise resulting from failure to do so does in fact upset most DACs quite badly. The early CD players were designed, on the whole, by a bunch of analogue engineers attempting to teach themselves RF (by comparison) design, and it took a while but the problem is now understood.
So that was a good example of enough subjectivists saying "There IS a bloody difference" and the engineers finally going looking to see what it might be, rather than making the same old measurements to "prove" there was no problem.
So here we are with mains cables. I'm an engineer. I'm an audiophile. I've built some of my own electronics. I've bought mains cables, I've constructed mains cables in various bizarre topologies, at various times, according to various theories. What I'm trying to say is that I have enough cables to play with that I'm not wedded to any one being bright and shiny because I've just paid for it. They all just live in a box in a box in the garage. And I can hear differences in the sound of some of my pieces of equipment, and those differences are reproducible (at least to the satisfaction of a few friends in an amateur blind test) with different cables.
I'm not alone, lots of people can hear these differences, if they actually sit and listen to music, rather than using it as background noise.
So the question we should be asking, just as in the CD-is-crap case 20 years ago, is not whether these people are sane but why they are reporting what they're reporting.
I have a theory, for example, but it's just a theory and I lack the measurement equipment (and the will) to prove it, but those of you with relevant experience may care to consider it. Most hifi kit contains relatively crude power supplies. You have a huge transformer, a bridge rectifier and some vast capacitors to act as a DC reservoir. So in normal operation you are barely clipping the tops off the incoming mains signal for a tiny fraction of a second, but you're doing so into an incredibly low impedance. As the diodes switch on, you'll get a sudden surge of current, at a level many times that which you might expect. That turn-on edge, such a sudden step-change in current, says Mr Fourier, transforms into an infinite (or, as I learned at school, at least to the end of the blackboard...) sequence of generated frequencies. Oh look, we've just made RF out of the very small impedance in a mains plug and socket. And these RF bursts will be coming in at 50 or 100Hz. And if you go look at household mains, especially with the plethora of SMPSes in every home, you will find that it is quite filthy - anyone with a scope can see that the tops are often clipped and there are long harmonic sequences all over it. If you think that the household mains looks anything like the nice sine wave we learned about in school, I suggest you go look.
So if you follow that, or perhaps I should say if you can swallow that, then it follows that a cable or filter that attempts to prevent RF entering the equipment may well turn out to be a good thing. How good a thing will depend very much on how well the designer of the kit was at designing for inherent RF rejection (in the case of my own home-made kit, the answer to that is Not Very, I freely admit).
So, a challenge. Instead of taking the piss, go work out what's actually going on. And if you're not willing to do that, then shut up :-).
Anyways. Yes, you do have an argument of sorts. But /this here kettle cord*/, presented as a silver bullet, the act of which was found to be contrary to relevant advertising standards, would be much like adding a gold-plated marble tube section to miles and miles of sewer on the premise that even if you put nuclear waste mixed with toxic chemicals in on one side, spring-clean water would come out the other.
Methinks that well deserves a healthy dose of ridicule and derision. Fixing shoddy PSUs in audio gear I'll gladly leave to PSU engineering types.
* Even if not pedantically-correct, I'm going to use the term anyway.
> I'm going to get flamed
I expect so.
> Well, the digital-is-crap brigade didn't go away
Many nonsensical theories don't go away. That doesn't mean there is any truth to them.
Digital reproduction can give excellent duplication of the sound that the recording engineer put down onto the media in the first place. When CDs first came out, this was very different to the peaky EQ that many people were used to from vinyl - so although the fidelity on CD was very much better, it didn't sound like the vinyl. The fact that it sounded more like the original source doesn't actually matter to most people - they like what they're used to.
Nowadays, of course, we've got all the "digitally remastered" nonsense that's hammered together by some monkey with no idea what the word "clip" means, who thinks those red LEDs in front of him are beat indicators, or something...
> All but the most diehard digital clown now accepts that recovering and
> preserving a decent clock is actually quite hard
Cobblers. Stable clock generation is easy. Remember that you don't need to sync the clock to anything else - you just need a stable source. It's easy.
> I'm not alone, lots of people can hear these differences
No they can't. Unless a cable is actually failing in some way - either being noisy or microphonic through crap construction, or simply not rated up to the task in hand, there is no difference. It's simply a triumph of belief over evidence. And with digital cables, even noise has no effect unless it is sufficient to destroy the signal entirely.
> why they are reporting what they're reporting.
Because they believe they have some knowledge that the rest of the world does not. It's a common fallacy - and easily disproved. But there will always be people who believe it, just as there will always be people who believe they have been abducted by aliens or other such nonsense.
> That turn-on edge, such a sudden step-change in current
It is *not* a step-change. You seem to be visualising this with "ideal" components. Real circuits have distributed RLC; for most purposes it can be ignored, but it is what prevents infinite currents occurring.
> transforms into an infinite ... sequence of generated frequencies.
A true step-change would generate an infinite series of harmonics - but you do not have that situation.
Additionally, the current flow through the rectifier is not coming from a fixed voltage source - it's coming from an AC drive (typically the secondary of a transformer), so the voltage in to the rectifier ramps up gradually.
And even if some harmonics are generated in the PSU, a half-decent unit will filter them out.
Sorry, but your pet theory is just wrong.
> if you go look at household mains ... you will find that it is quite filthy
This is why PSUs filter the input.
> anyone with a scope can see that the tops are often clipped
No they're not. Whilst there is often a goodly amount of noise on the mains, a clipped sinusoid would mean that there is a DC voltage across the primaries of many transformers during the clip. Given the current availability on a ring main, that's a good way to set light to stuff...
If you're seeing clipping on a scope, I suspect you do not understand the limitations of your scope, because that is not what is actually happening.
> So if you follow that, or perhaps I should say if you can swallow that
I don't. It is bogus.
> go work out what's actually going on.
I would echo that sentiment. Your assertions are decidedly dodgy.
Vic.
I think you need to go back and do the math's and put this into a circuit modeler. In a real circuit such as you describe, and even such a crude design as a you have described (and I sincerely hope that the sort of amplifier that people pay thousands for) will not look like that, you simply will not get inifinite steps as you describe. Firstly diodes don't turn on instantaneously when subject to a sine wave input, they also have a finite forward resistance which decreases as the forward bias increases. That transformer has resistance which will damp the current flow and it simply will not create a step change. It's also easy enough to measure.
In any case, this sudden current flow is most evident at power-up when the smoothing capacitors are discharged. During normal operation, this simply won't happen as it only has to cope with the ripple current. In any event, if the power supply was generating bursts of RFI at intervals of 100Hz then it would be easily measurable. You'd see it on the amp output, you'd be able to measure it on harmonic distortion. In any event, what on earth (no pun intended) would that have to do with the mains power cable?
This is not to say that there aren't dodgy power supplies that damage audio performance. However, it's not rocket science to design a proper one, and if that's done (including filtering), then the power cable is irrelevant provided it's not so poor that it can't deliver the mains.
Nope - it's not a joke, or if it is it's an expensive one perpetrated on gullible fools. You can genuinely buy audio cables with direction indicators. Originally they used to give instructions as to which end was to be conencted to what piece of equipment (e.g one end the speaker, the other the amp). Unfortunately some people found they'd made a mistake in installing the cables the wrong way round and found that, lo and behold, that they hadn't heard it. Of course the explanation wasn't that the directionality is a myth, but that magically the directionality mattered, but which direction depended on your particular circumstances and type of kit. Simple solution, some manufacturers kept the magical quality of directionality by putting arrows on the sheaths, but you, the audophile, with your infallible ears will decide which direction to connect the cable and the arrows will enable you to reconnect the same way.
Yes, and people do believe this stuff. The fact that no measuring equipment on earth can detect the effect is irrelevant. There are others - some people believe in cable "burn-in". You have to run it in for several tens of hours before it gives of its best. You can even buy special pieces of equipment to "burn in" your audio cables.
(Nb. there are some valid circumstances where a shield should only be connected at one end, but that's not a matter of directionality but of avoiding nasties like earth loops. In that case what connector is at what end does matter, but then the cable isn't symetrical).
A number of people have, quite understandably, mentioned error correction.
Afaict, at the time I am writing this, no one has yet mentioned the fact that error correction is not infallible. If things are sufficiently bad, or you are sufficiently unlucky, errors can occur that will not be corrected. Mostly these errors will still be detected, but sometimes they will be undetected and the data that arrives will be plain simple wrong AND (at the digital level) NO ONE WILL KNOW. This is an inevitable characteristic of most error correcting codes.
In a pure-digital setup where the numbers are not representing an analogue quantity, you typically give up and do a retry at that point.
In a mixed A-D-A setup, it is theoretically possible for a design to attempt to guess the missing data e.g. by interpolation from the preceding and following samples (or some other digital or analogue filtering magick). I don't know if that happens in practice, but it's conceivable. Anybody know for sure?
Anyway, this real world digital kit that's so perfect, what does it actually do with an error that it has detected but not been able to correct? Just ignore it (see link below) and rely on filtering/interpolation, hoping that no one will notice?
Are there counters anywhere that keep track of corrected and uncorrected errors on the link?
Your $20 DSL modem/router has the relevant counters and plenty of geeks (sorry, people) know how to use them. It also has the ability to request a retransmit (via the IP protocol).
Setting to one side the ability to request a retransmit, are there no error counters in the hardware for these digital entertainment protocols?
http://arstechnica.com/civis/viewtopic.php?f=6&t=275120&p=6271817
"If you think that the household mains looks anything like the nice sine wave we learned about in school, I suggest you go look."
Indeed. Been there done that. Some other interesting stuff in your post too (e.g. re current pulses/ringing from SMPS).
There is a whole load of junk talked on this subject to relieve gullible people of their money.But error correction is not a panacea, and having an error corrected digital link without commonly available tools to check whether it's working right or not is just stupid (or someone in the designer/manufacturers is hiding something).
>> If things are sufficiently bad, or you are sufficiently
>> unlucky, errors can occur that will not be corrected.
http://en.wikipedia.org/wiki/Reed%E2%80%93Solomon_error_correction
>>NO ONE WILL KNOW.
http://en.wikipedia.org/wiki/Reed%E2%80%93Solomon_error_correction
>>In a mixed A-D-A setup, it is theoretically possible for a design
>> to attempt to guess the missing data
http://en.wikipedia.org/wiki/Reed%E2%80%93Solomon_error_correction
>>Your $20 DSL modem/router has the relevant counters
http://en.wikipedia.org/wiki/Reed%E2%80%93Solomon_error_correction
http://en.wikipedia.org/wiki/Transmission_Control_Protocol#Error_detection
http://en.wikipedia.org/wiki/Checksum
>>are there no error counters in the hardware for
>> these digital entertainment protocols?
http://en.wikipedia.org/wiki/Error_detection_and_correction
>>"If you think that the household mains looks anything like the nice sine wave""
http://en.wikipedia.org/wiki/Electronic_filter
>>(or someone in the designer/manufacturers is hiding something).
http://www.google.co.uk/search?hl=en&source=hp&biw=1920&bih=922&q=reed+solomon+decoder+datasheet&aq=f&aqi=&aql=&oq=
http://en.wikipedia.org/wiki/Cdparanoia
> no one has yet mentioned the fact that error correction is not infallible.
Yes they have. That's why these digital links are described as "working" or "not working". The latter is when the signal contains uncorrected errors.
> the data that arrives will be plain simple wrong AND (at the digital level) NO ONE WILL KNOW.
No.
Whilst there is a mathematical probability of a random data corruption causing a valid packet hash, the chances are vanishingly small. You're never going to see that.
> I don't know if that happens in practice, but it's conceivable. Anybody know for sure?
In TV, for example, there are various "error covering" modes, but these usually involve just repeating a previous sample - this is why you get screen freeze when the signal goes very bad. This is generally unacceptable for audio because you get audio tics, which are very distracting.
What you do *not* do is to try to make up the data you have missed. There is insufficient information about it, so any guesses will be badly wrong.
> what does it actually do with an error that it has detected but not been able to correct?
Depends on the severity. If you're missing a couple of MBs, you typically display the picture anyway - it'll have a purple / green stripe in it, but most of the picture will be there. If you miss most of the picture, you start by freezing the display for a short while, and then blanking it if you don't get valid signal quite quickly.
For audio, you mute.
> Just ignore it (see link below) and rely on filtering/interpolation, hoping that no one will notice?
There is no such hope - if the data is missing, the user will notice. You make the best of a bad job, and hope the stream recovers.
> Are there counters anywhere that keep track of corrected and uncorrected errors on the link?
No. If the stream is degraded, it needs to be fixed. Carrying counts is fairly pointless.
> Your $20 DSL modem/router has the relevant counters
A DSL modem is carrying asynchronous data. An A/V link is carrying isochronous data. There is significantly less you can do about errors in the latter case. Additionally, a modem is dealing with WAN signals, where latency is expected. An A/V link is dealing with local signals, where latency is minimised. These situations add up to one system that can use retry protocols, and one that cannot.
> There is a whole load of junk talked on this subject
There certainly is.
> an error corrected digital link without commonly available tools to
> check whether it's working right or not is just stupid
Not so. It is appropriate for the medium.
> or someone in the designer/manufacturers is hiding something
Or, alternatively, yet another AC on an Internet forum doesn't actually know what he's talking about.
Vic.
"Mostly these errors will still be detected, but sometimes they will be undetected and the data that arrives will be plain simple wrong AND (at the digital level) NO ONE WILL KNOW."
"Are there counters anywhere that keep track of corrected and uncorrected errors on the link"
You mean to count the errors that were undetected?
This post has been deleted by its author
"Higher quality cables may be capable of longer runs, but they won't improve picture quality."
Here's a mystery - I still do not believe that bog standard telephone cable can carry signals of up to 2/5/8 Mhz, so how does ADSL work?
Yes, I _do) have a copy of the Ladybird Book of Computing in the pocket - they can't explain it either.
OK - back to my physics days. The reason why ordinary phone cable can carry ADSL signals is that (from the exchange) it's a balanced pair - at least until you hit the household wiring when ring-line separation (at least in the UK) can be a problem as can some nasty home wiring kits. Both are easily dealt with.
Note that the pairs from the exchange are fairly loosely twisted, as they were designed for noise rejection at a fairly narrow range of audio frequencies. Nevertheless, it's good enough for ADSL. What essentially happens with ADSL is that it uses a relatively low raido frequency band (about that of MW/LW) up to about 2Mhz. That bandwidth is separated into a number of sub-channels of, I think, about 20Khz each. Each sub-channel is assigned a number of bits depending on how good the SNR ratio is as the receiving end. The higher the frequency, the more the signal is attentuated (largely due to skin effects with I did the calculation - at higher frequencies less of the copper is used, and at the characteristic impedance of phone lines, then the resultant increase in resistance seems to be the main cause of degradation). Anyway, the upshot of this is that the higher frequencies get attenuated more and can carry fewer bits.
Each sub-channel is modulate using an encoding system called QAM (from memory) which uses both amplitude and phase modulation. Indeed it's what modems used in the dial-up days before broadband, but confined to audio frequencies (and the reason it was confined to audio frequencies was simply because the signal had to pass through a digital exchange system than itself could only encode 64Kbps, in Europe, or 56Kbps, in the US). As ADSL signals only go as far as the DSLAM in the exchange (or streetbox), it never hits the exchange.
Anyway, really clever stuff is how the signal is how the signal is modulated and de-modulated. Back in the old days it was done using inductors and capacitors and analogue circuits and an ordinary phone line would be lucky to hit 9600baud and the modems were physically huge. However, these the modulation is essentiall created as a digital signal in the first place which is then put onto the phone line using a digital-to-analogue converter (DAC). As the far end, the very much attenuated signal (perhaps reduced in power by a factor of a million or 60dB) is converted back into a digital one using an analoge to digital converter. Then a bit of magic happens - the string of numbers representing the, buy now, heavily distorted modulate signal is def into some very clever mathematical algorithms which essentially reconstruct the relevant bit streams.
This bit of magic is called Digital Signal Processing (DSP) and is at the heart of all modern high speed communication and digital broadcasting. DSP is truly one of the wonders of the modern age, and is only hard-core mathemeticians.
So those that say that there is no such thing as a digital signal are right - well, at least over cabling of any length.
If your kit's power supply isn't well enough designed to reject significant noise from the mains input then the chances are it's not going to have had much effort put into amp design either (or anything else for that matter) so buying a 1250 quid mains lead isn't going to make your day any better.
Similarly, if your 99p HDMI lead is causing dropouts (and any errors on audio or video will be hugely obvious), splash out on a 1.99 one with a little bit of copper between the connectors. That'll do. No, error correction is not a panacea. But if the 2b/10b, 4b/10b and 8b/10b coding on HDMI's not up to the job then you've either got a *really* badly made lead or some serious noise around. And lose the paranoia. No-one extracts error correction stats because the recovery is entirely automated and done at such a low level (i.e. not software) it would be annoying (not to mention pointless) to do. All anyone cares about is worky/no worky, not how hard the error correction's working.
@Vic
"one system that can use retry protocols, and one that cannot."
Exactly my point.
In a DSL setup, if an error is detected but not corrected, the data "goes missing" at the DSL layer, and if you're lucky the IP layer retries. Errors which are detected are counted, separately for correctable and uncorrectable errors. Therefore you can tell the difference between an occasional burst of errors due to external factors, and a consistently degraded link due to marginal transmission quality.
It appears there is no such option in these entertainment connections, instead if an error is detected but not corrected they attempt to replace the missing data with a fake, and if the error is not detected the incorrect data must by definition get through and no one is any the wiser till it hits the audio or video.
"the chances are vanishingly small. You're never going to see that."
The chances of an error are indeed very small per frame/cell/packet, the number of frames/cell/packets/whatever is however outrageously high. Therefore errors will happen from time to time, and could in principle be counted (as per DSL modem). Whether any given error burst will be seen (or heard) by the end user is a slightly different question. The chances of an undetected error are even smaller, but that just means it'll take longer for one to occur.
@AndyMc
"No-one extracts error correction stats because the recovery is entirely automated and done at such a low level (i.e. not software) it would be annoying (not to mention pointless) to do."
I'm not paranoid. I'm just aware of what "industry best practice" might be (as exemplified by $20 DSL modems with error counters as an architectural requirement), and what makes a poor/cheapskate design (an error correcting link with no performance indication except when the user sees the result of errors).
@Daniel Palmer
Thank you Daniel, I'm one of the many readers who will know what Reed Solomon error correction is. I even know what turbo codes are, and a whole load of other stuff. So what? No error detection/correction is infallible, not Reed Solomon, not turbo codes, nor any other. Did you actually have a point to make?
"I'm just aware of what "industry best practice" might be (as exemplified by $20 DSL modems with error counters as an architectural requirement)"
Erm, that'll be the wrong industry's best practice.
I suspect you'll find that the main reason for the quantity of low-level info presented by DSL modems relates to the amount of difficulty a very significant % of users have getting reliable high-speed connections. If you go out and ask your friends, assuming you have some, how many have link, latency, throughput or data loss problems with their broadband vs. their HDMI link from STB to TV, I think you'll understand why it would be a pointless exercise (and increase the cost to the end-user) to implement lots of low-level debug on every HDMI-equipped box.
Struggling to find something in the message to attack, are we, so reverting to the usual fallback?
Anyway, the DSL stuff is usually on an SoC; impementing counters basically comes for free, in a box costing $20 or so.
The common consumer kit (HDMI sinks?) in this HDMI picture costs what, twenty or fifty or maybe even a hundred times the typicall DSL box, but you and/or the vendor presumably say there's no money for half decent diagnostics so customers or installers can see how well things are working? Not even at nearly zero marginal silicon cost to the vendor?
Oh yeah, some poor soul would have to write some software for it, and since most consumer electronics software already struggles to do what the customer paid for it to do (how many PVRs have basically junk software?), where would be the RoI on that? After all we couldn't possibly let folk ssh/telnet in to the box and read from /dev/kmem could we (which is basically zero development cost)?
HDMI. Highly dubious media interconnect.
I don't actually mind if folks have taken an active decision to degrade the possible functionality of this kit (despite the fact that the diagnostic functionality would have an insignificant marginal cost).
What I do mind is this ridiculous "it's digital and it's got error correction therefore nothing significant can go wrong". It's just wrong.
Have a lovely weekend.
> "one system that can use retry protocols, and one that cannot."
>
> Exactly my point.
then you haven't thought through what point you're trying to make.
Isochronous data is real-time. If you retry transmission, it is late. This would show up as pauses or drops in the displayed data - and remember that you will have do duplicate the artefact on both audio and video streams if they are to remain synchronised. This is not feasible for consumer equipment - if you really have lost the data, by far the least noticeable way of dealing with it is just to give up on that chunk and start again. Attempting to get a retransmission would make the error very much worse.
> Therefore you can tell the difference between an occasional burst of
> errors due to external factors, and a consistently degraded link due
> to marginal transmission quality.
I have absolutely no idea what you're trying to prove now. So what if we can detect trends in the error rate? We can't go back in time and make those errors not happen - which is what is needed to relay isochronous data on time.
> It appears there is no such option in these entertainment connections
Some equipment may hold historical data for debug purposes - but that is all. Kit generally doesn't offer up such debug info because it is of no use to a user.
>"the chances are vanishingly small. You're never going to see that."
>
> The chances of an error are indeed very small per frame/cell/packet
Have a look at *how* small.
> the number of frames/cell/packets/whatever is however outrageously high.
Not high enough.
> Therefore errors will happen from time to time
Random errors creating valid has checks are a mathematical possibility only. If I had a tenner for every time it had ever happened, I would have nothing.
> and could in principle be counted (as per DSL modem).
Now you're confusing two things: whether errors occur (they do), and whether that error creates a valid packet (they don't).
But counting errors serves no purpose: you can tell if the link isn't working because you can see or hear it. Attempting to do anything else means you are breaking the real-time nature of the signal - and that will cause far more problems than it solves (as well as being undesirable in the first place).
Vic.
As an amateur who has dabbled in electronics for some 60 odd years, I can't help thinking that a couple of capacitors across the mains input connections of a piece of equipment would do a decent job of filtering out RF, coupled, if necessary, with with a couple of RF chokes in series with the mains input wires. One is then able to spend the £1249.70 saved on a world cruise.
Ticket in the pocket.
"the only person who wants pages of pointless info to make crappy interfaces even less comprehensible :)"
Suppose the "errors detected - corrected, uncorrected" information *was* there somewhere, even tucked away in a dark corner where it didn't interfere with the market's appreciation of the sylph-like beaty of the UI as shipped.
If it was there, how long would it take for someone to prove that folks like the cable manufacturers in this picture, and maybe even outfits like Belkin, were (in general) selling vastly overpriced snake oil? How many people would want that?
More to the point, how many people would *not* want that (other than your good self)? Would such information be sufficiently dangerous (to the hi-fi media and the likes of Belkin and Russ) that it would be impermissible to provide that functionality?
I studied elec/electrical eng at university (graduating about 20 years ago) and even back then I was amazed by the marketing efforts selling products claiming dubious levels of performance. I even considered whether I could concoct devices which would be functional but expensive which could offer genuine performance improvements specifically targeted at the rich, but I didn't think I'd be able to make a living at it. Boy, was I wrong :-(
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