Posts by John Dawson
8 posts • joined Thursday 3rd May 2007 14:30 GMT
Posted in Skyfall makers 3D printed Bond's DB5
Cinema pricing can be OK
Saw the movie last night at my local Picturehouse in Cambridge with digital projector and a THX certified sound system. Very impressive and my partner, who is not a big JB fan,really enjoyed it too.
With membership and Orange Wednesdays concession it cost less than 7 GBP for two tickets. Yay!
John Dawson
Lenovo
Lenovo offer a 3 year carry-in warranty on their T series machines - I swear by these and have owned them back from the IBM days. The warranty is transferable too, so if you buy one a year old on e-bay you still have two years left. So far I have never had a machine fail in the three year period anyway.
IBM/Lenovo also have comprehensive service manuals on-line so you can fix most faults yourself outside warranty.
Works for me :)
Posted in Arcam rPac
Re: jitter-free analogue signal
Umm... to which TI DAC are you referring? It is certainly not the PCM5102. Perhaps you are thinking of the PCM270x family? These parts are limited to 16 bits 48ks/s and have a crude clock recovery system that produces LOTS of jitter related products in the audio output. They are fine for simple USB speakers etc but are not hi-fi in the highest quality sense of the word.
Please read my main posts in this thread to find out more.
John Dawson
Posted in Arcam rPac
Re: jitter-free analogue signal
Jitter is indeed about small timing errors in digital signals, below the amount needed to cause real bit-errors.
This would not normally matter except that in digital audio it is necessary to have a really clean clock at the audio DAC (or ADC); otherwise errors in the timing are equivalent to linearity errors in output level from one bit number to the next.
The problem with digital audio interfaces (S/PDIF, HDMI and USB for example) is that no clean master audio clock is actually transmitted over the interface - you have to reconstruct it at the receiving end. This is not as easy as it sounds. One way is to use a FIFO and clock out using a clean clock and ask the transmitter to vary its rate so as to avoid overflow/underflow. This is impossible with S/PDIF as it is one way but is possible with USB provided you use the method. There is not much silicon around that actually does this - Arcam is one of the few companies to implement it in all its USB DACs right down to this inexpensive one. The other solutions use the 1millisecond frame rate associated with USB and this produces a LOT of timing errors i.e. jitter which modulates the audio output signal.
As to what it sounds like - well that depends on both the amount and frequency spectrum of the jitter. Where it is intrusive it can be likened to looking at a scene through a dirty window - when you clean it (remove the jitter) the whole picture cleans up too.
HTH - it is intended as a serious answer.
John Dawson
Posted in Arcam rPac
Re: It's a USB powered DAC implemented with asynchronous transfer protocol...
Heh - one obvious typo - ear should of course be gear - oops!
Posted in Arcam rPac
It's a USB powered DAC implemented with asynchronous transfer protocol...
...and it's aimed mostly at laptop users, so it needs low power consumption. Nevertheless you get something with around 110dB signal to noise ratio which is capable of driving headphones of any impedance to a decent sound level without audible distortion or noise. There's even a handy volume control on the box to save faffing about with a mouse. You don't get all this from any computer motherboard or laptop I know of. Sure some premium sound cards might perform as well (and quite possibly even better) but that's not what this product is competing with.
What we observed is just how many people store their music libraries on a laptop or PC, spend lots of money on headphones (I am talking hundreds of pounds) and yet don't have decent electronics to drive those headphones. To do this well for 150UKP retail is actually pretty impressive imho.
And not one of you referred to the method of ensuring proper clock recovery so that the chosen DAC chip can work to its full potential over USB. I promise you it makes a BIG difference to sound quality when sending audio over USB. It's also expensive to implement - there's a fancy XMOS processor in the box..To anyone suggesting all DACs etc sound broadly the same I suggest you read up and understand the required overall architecture before opening your mouths and going off half cock. I have given lectures and workshops to the AES on this topic.
My admission here - I was involved in the architecture of the rPAC and I am a bloody good audio electronics engineer with a deep understanding of the difficulties of analogue and mixed signal design. I also have 30Ks worth of my own ear to measure this stuff properly. On the other hand I didn't write the marketing blurb or have anything to do with the reviewing process.
Hey if you like music and have decent headphones why not try an rPAC? If you purchase it mail order you can no doubt demand your money back in 7 days if it doesn't do what it says on the tin. It won't take that long to find out ;)
John Dawson
oops - rumour is wrong again (probably)
If you go back to the source of all this (in Germany IIRC), you will find it is supposed to cost 400 Euros MORE than a standard Blu-ray only player. If you think about it that makes a lot more sense and implies a price of more like 800 - 1000 Euros. Anyway we will all know at IFA next month.
See for example http://www.electronista.com/articles/07/07/04/samsung.hybrid.launch.info/
John Dawson
remember li'l abner guys?
I thought I wasn't having a senior moment, though sadly they do get commoner these days. Way back in the 50s my auntie from Canada used to send me the Sudbury Star comic section, wherein there was a strip called Li'l Abner, featuring life in the hillbilly town of Dogpatch and including a guy who ran the Skunk Works, err... skinning skunks.
A little googling throws up the story, as featured in El Reg in 1999, called What the Hell is a Skunk Work? See http://www.theregister.co.uk/1999/10/27/what_the_hell/
Shouldn't Lockheed be suing the estate of the (presumably) late Al Capp, author of the comic strip from which they stole the name? Or should the estate be suing Lockheed? Answers on a postcard please.
All the best,
John Dawson
