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The most common way retro machines made sounds were with programmable sound generators (PSG); there was a bunch of square waves, saw waves or noise channels at disposal. When technology evolved eventually FM-synthesis and sampling became most common.

A lesser common technique is an improvement of regular PSG, that instead of allowing only simple waveforms such as square wave, saw wave, etc... allows to load any waveform in RAM. Unfortunately I don't know the name (if there's one) for that technique. So far I know the following systems have that:

  • Gameboy but only for channel #3
  • The Famicom Disk Sytem (used alongside normal Famicom sound)
  • Namco 163 's sound expansion chip for some rare Famicom games (used alongside normal Famicom sound)
  • Some Konami arcade boards (I'm currently looking up as I don't remember the details)
  • The PC-Engine (known as the Turbo-Grafx 16 in the United States)

I wonder if there are other system based on this principle ?

Note : I'm not looking for systems based on samples, but on custom waveforms ("wavetable synthesis" is unfortunately used for both) The differences are that for what I call "waveform synthesis" in this question is:

  • There is no settable length or loop point, no (hardware) attack phase, only a fixed-size loop of samples, typically of 16, 32 or at most 64 samples.
  • Memory for waveforms is small, and typically part of the sound chip itself (the sound chip doesn't access RAM to read samples).
  • Memory for waveforms is per-channel, i.e. each sound channel has it's own waveform defined somewhere fixed, and cannot "point" to different waveforms at runtime.
  • Low bit-depth, typically 4 or 5 bits per sample instead of at least 8 bits for sampling synth
  • The audio chip can play custom waveforms without CPU intervention. While it might be possible to play advanced samples with CPU trickery and/or monopolizing the CPU at this task, just like in other, more classical Programmable Sound Generator (PSG) chips, this does not count.
  • You already mentioned a mixup in name, but the technology to do sounds consits of even more variants. So would you mind to specify a bit more detailed what falls into your definition? What does a 'custom wave form' mean here? Is a C64 SID fiting? Or does it need to be within a sound chip, or is a CPU plus an 8 bit DAC, like already the first Mac had, also qualify? – Raffzahn Aug 19 '18 at 11:00
  • "Custom waveform" in my book would also apply to anything that is a .mod sample - This has been implemented on lots of sound hardware. – tofro Aug 19 '18 at 12:06
  • I'm not sure what the difference between what you call "sampling synthesis" and "custom-waveform synthesis" is supposed to be. The Gameboy's channel 3 and the PC-Engine's sound chip both use sample-based synthesis, they sounded less realistic than other later sample-based synthesis implementations mostly because they used 4-bit and 5-bit samples respectively. – Ross Ridge Aug 19 '18 at 13:41
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    Your definition of "waveform-synthesis" seems arbitrarily made to fit the examples you've listed and exclude everything else. It seems likely you'll just adjust your definition to exclude or include anything else that might be suggested based on whether you feel it should count or not. For example, why doesn't the PC-Engine's ability to dynamic adjust the frequency of sample playback not violate your "The chip will send data from the waveforms directly to the DAC, without filtering, resampling or anything. Only volume change might be possible." rule? – Ross Ridge Aug 19 '18 at 15:28
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    Is the term you're looking for "Direct Digital Synthesis" (DDS)? – snips-n-snails Aug 19 '18 at 23:24

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