Sound chips

I'm sitting here in the middle of the night listening to Amstrad CPC music. For those of you who don't know, the CPC had an AY-3-8910. The same chip could be found on late Spectrum models and apparently also in the Research Machines Nimbus. The Atari ST uses a Yamaha clone of the same chip, called YM2149. I believe that the MSX uses such a chip, too. However, when running a Windows programs called STSOUND, which emulates said chip, I saw that the ST drives its blipp-blopp chip at 2 MHz, whereas the Spectrum and Amstrad run their chips at lower rates. In what way does this really affect the sound? The change is perfectly audible, but what does it do? Does it just affect the throughput, replaying the tune faster, or does it affect the waveforms, and in that case, in what way? Another question: The Sega Master System and the BBC use an SN76489 sound chip. Both the AY/YM chip and the SN one are "PSG" chips. That means that they've got three square wave channels and a noise channel which may (at least on the AY/YM) be mixed with the square channels. But are those chips related, or are they just chips which happen to use the same techniques? BTW, I must add that the PSG chips are really pathetic in comparison to the SID. I suppose they beat the Atari's Pokey, though. =) -- En ligne avec Thor 2.6a. A conservative is a worshipper of dead radicals.