Reply to post: Re: What we need @cream wobbly

ZX Spectrum reboot latest: Some Vega+s arrive, Sky pulls plug, Clive drops ball

ThomH Silver badge

Re: What we need @cream wobbly

I'm not sure it's accurate to say that other micros typically had to live-toggle a bit. Of the successful ones I'm pretty sure that's only the Apple II and the 16/48kb Spectrum.

None of them is a match for the feature set of the SID, but the 128kb Spectrum and CPC share the AY which is three channels of square wave and/or noise with volume envelopes; the 8-bit Atari has the POKEY which is four channels of more-or-less square wave; the BBC has an SN76489 which is three square waves plus a noise channel, etc.

The SID's killer feature is phase accumulation for pitch selection rather than simple division, giving much finer control — in a SID there's a 24-bit counter, the top few bits of which are used to form the output level, and an amount that is added to it at each cycle. Plus some analogue filters. On the other chips there is the input clock and then there is an integral divider. So you're controlling the reciprocal of pitch, reducing useful precision.

Nevertheless, the other chips don't require active CPU participation as the 48kb Spectrum does, and the musical opportunities are still fairly decent.

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