Reply to post: Re: What we need

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

Michael Strorm

Re: What we need

> cream wobbly; "The C64 also benefited from the SID audio synth-on-a-chip. Unlike "chip music" from other 8-bit micros which typically waggled a DAC around to make PWM noise"

(Edit:- @ThomH; If I'd refreshed the page before posting this, I'd have seen that you'd already made much the same point in your reply!)

That's true as far as the original (pre-128K) Spectrum goes- along with some other machines (IIRC the Apple II and Dragon 32). However, it's far from accurate to imply that DAC waggling was "typical" of the majority of 8-bit computers.

Many had separate sound chips:-

- The Atari 800 (which came out in 1979) had a four-channel custom chip called POKEY.

- Several 8-bit computers used the Yamaha AY-3-8912 sound chip, including the Amstrad CPC, the Spectrum 128 (though admittedly that came later on), the Oric-1 and Atmos, and MSX.

- Several more used the Texas Instruments SN76489, including their own TI-99/4A, the BBC Micro and the Coleco Adam (and the ColecoVision console it was based on)

Others had sound generation integrated into multi-function custom chips:-

- Commodore's own VIC 20 (i.e. the direct predecessor to the C64) already included tone generation facilities as part of the VIC chip

- Similarly, the Commodore 16 and Plus/4 included tone generation within the TED chip

- Even the relatively primitive Atari VCS (admittedly not a personal computer) had two-channel audio generation as part of the TIA chip.

The point here isn't whether or not these were up to the standard of SID. It's that they were separate sound generation facilities that- like the C64's- freed the CPU to do other things.

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