3 ms·

Although its sound is legendary, I can imagine it's not that complicated a chip. Had anyone ever tried to replicate it with discrete components?

bayindirh 3y ago
The sound of SID comes from its architectural decisions and how the die behaves as an integrated circuit. IIRC, SID has no real mute on the outputs, so oscillators and output stage is always active. This, in turn, injects its legendary background noise to the generated sound regardless of there's a wave being generated or not. Moreover, the distortion itself is coming from the internal noise of the die itself, as a secondary effect of being an integrated circuit, plus its fabrication technology. As a result, the sound of a SID chip is result of its design plus the secondary effects introduced because of its fabrication process. This is what makes simulating a SID very hard. You need to characterize and formulate these secondary effects and inject them to your pure generation (design) simulation real-time, without much processing overhead. This is really hard. Maybe not in the math department, but integration, coding, optimization and stabilization department. P.S.: This is why Machinae Supremacy started making music with real SID chips.
- whizzter 3y ago
  In addition to this (and this is a huge part of what makes it hard to emulate) is that parts of the chip works in the analogue domain, that combined with the added outputs/noise/etc is what makes for the richness to be so hard to emulate.
  - bayindirh 3y ago
    You're right. I forgot that some parts of SID is actually analog. Thanks for the addendum.
- radarsat1 3y ago
  Ah I see that's pretty insane. So the character of the sound doesn't just come from the circuit but is really intrinsic to the chip design. That's some really clever engineering.
  - GuB-42 3y ago
    It wasn't "clever", it was all about cost-cutting, and from a high fidelity perspective, it was a terrible chip. But, that gave it character, and people grew to love that sound. Maybe it was a fluke, maybe nostalgia, maybe people at Commodore had a good ear when tweaking the circuit and made something sound good out of the little budget they had because they knew they couldn't go for hi-fi (that would actually be clever). This is a bit like the TB-303, a terrible bass synthesizer that ended up revolutionizing electronic music. Or overdriven guitar amps that became the staple of the hard-rock/metal genre.
    - AlbertoGP 3y ago
      > Maybe it was a fluke, maybe nostalgia, maybe people at Commodore had a good ear when tweaking the circuit and made something sound good out of the little budget they had because they knew they couldn't go for hi-fi (that would actually be clever). In the words of the engineer that designed the SID chip, Bob Yannes who founded the synthesizer company Ensoniq after he left Commodore in 1982: > “Actually, I was an electronic music hobbyist before I started working for MOS Technology (one of Commodore's chip divisions at the time) and before I knew anything at all about VLSI chip design. One of the reasons I was hired was my knowledge of music synthesis was deemed valuable for future MOS/Commodore products. When I designed the SID chip, I was attempting to create a single-chip synthesizer voice which hopefully would find it's way into polyphonic/polytimbral synthesizers.” > “The SID chip was my first attempt at a phase-accumulating oscillator, which is the heart of all wavetable synthesis systems. Due to time constraints, the oscillators in SID were not multiplexed, therefore they took up a lot of chip area, constraining the number of voices I could fit on a chip. All ENSONIQ sound chips use a multiplexed oscillator which allows us to produce at least 32 voices per chip. Aside from that, little else of SID is to be found in our designs, which more closely resemble the Mountain Computer sound card for the Apple II (the basis of the Alpha Syntauri system). The DOC I chip (used in the Mirage and ESQ-1) was modeled on this sound card. Our current designs, which include waveform interpolation, digital filters and digital effects are new designs that aren't really based on anything other than our imaginations.” > “The issue wasn't budget, it was development time and chip size constraints. The design/prototype/debug/production schedule of the SID chip, VIC II chip and Commodore 64 were incredibly tight (some would say impossibly tight)--we did things faster than Commodore had ever done before and were never able to repeat after! If I had had more time, I would have developed a proper MOS op-amp which would have eliminated the signal leakage which occurred when the volume of the voice was supposed to be zero. This lead to poor signal-to-noise ratio, although it could be dealt with by stopping the oscillator. It would also have greatly improved the filter, particularly in achieving high resonance. I originally planned to have an exponential look-up table to provide a direct translation for the equal-tempered scale, but it took up too much silicon and it was easy enough to do in software anyway.” https://web.archive.org/web/20070222065716/http://stud1.tuwien.ac.at/~e9426444/yannes.html https://web.archive.org/web/20070222065716/http://stud1.tuwi... https://en.wikipedia.org/wiki/Bob_Yannes https://en.wikipedia.org/wiki/Bob_Yannes https://en.wikipedia.org/wiki/Ensoniq https://en.wikipedia.org/wiki/Ensoniq
- Mountain_Skies 3y ago
  Makes me wonder if the output could have been used as part of a better random number generator on the 64.
  - classichasclass 3y ago
    As it happens, you can snoop on the output of voice 3, and in noise mode it could indeed be used for random numbers. It generates a new value about every 26 processor cycles.
WalterSear 3y ago
It's a partially analog circuit.
- radarsat1 3y ago
  Yeah, exactly. So I was wondering of the same analog circuit has been built outside an IC (ie. discrete components) but according to the other response, the IC specifics are integral to the result, which is crazy and really cool.
  - exDM69 3y ago
    The original chip was built with 1970s NMOS semiconductor technology. While you can theoretically build the same analog circuitry using discrete N-channel MOSFETs, it will not capture the tone of the original. In particular the "operational amplifiers" used in the design were very simplistic things built out of just a handful of transistors and are very non-linear devices. It is possible to build a circuit that behaves similarly but it won't sound the same.

bayindirh 3y ago

The sound of SID comes from its architectural decisions and how the die behaves as an integrated circuit. IIRC, SID has no real mute on the outputs, so oscillators and output stage is always active. This, in turn, injects its legendary background noise to the generated sound regardless of there's a wave being generated or not. Moreover, the distortion itself is coming from the internal noise of the die itself, as a secondary effect of being an integrated circuit, plus its fabrication technology. As a result, the sound of a SID chip is result of its design plus the secondary effects introduced because of its fabrication process. This is what makes simulating a SID very hard. You need to characterize and formulate these secondary effects and inject them to your pure generation (design) simulation real-time, without much processing overhead. This is really hard. Maybe not in the math department, but integration, coding, optimization and stabilization department. P.S.: This is why Machinae Supremacy started making music with real SID chips.

whizzter 3y ago
In addition to this (and this is a huge part of what makes it hard to emulate) is that parts of the chip works in the analogue domain, that combined with the added outputs/noise/etc is what makes for the richness to be so hard to emulate.
- bayindirh 3y ago
  You're right. I forgot that some parts of SID is actually analog. Thanks for the addendum.
radarsat1 3y ago
Ah I see that's pretty insane. So the character of the sound doesn't just come from the circuit but is really intrinsic to the chip design. That's some really clever engineering.
- GuB-42 3y ago
  It wasn't "clever", it was all about cost-cutting, and from a high fidelity perspective, it was a terrible chip. But, that gave it character, and people grew to love that sound. Maybe it was a fluke, maybe nostalgia, maybe people at Commodore had a good ear when tweaking the circuit and made something sound good out of the little budget they had because they knew they couldn't go for hi-fi (that would actually be clever). This is a bit like the TB-303, a terrible bass synthesizer that ended up revolutionizing electronic music. Or overdriven guitar amps that became the staple of the hard-rock/metal genre.
  - AlbertoGP 3y ago
    > Maybe it was a fluke, maybe nostalgia, maybe people at Commodore had a good ear when tweaking the circuit and made something sound good out of the little budget they had because they knew they couldn't go for hi-fi (that would actually be clever). In the words of the engineer that designed the SID chip, Bob Yannes who founded the synthesizer company Ensoniq after he left Commodore in 1982: > “Actually, I was an electronic music hobbyist before I started working for MOS Technology (one of Commodore's chip divisions at the time) and before I knew anything at all about VLSI chip design. One of the reasons I was hired was my knowledge of music synthesis was deemed valuable for future MOS/Commodore products. When I designed the SID chip, I was attempting to create a single-chip synthesizer voice which hopefully would find it's way into polyphonic/polytimbral synthesizers.” > “The SID chip was my first attempt at a phase-accumulating oscillator, which is the heart of all wavetable synthesis systems. Due to time constraints, the oscillators in SID were not multiplexed, therefore they took up a lot of chip area, constraining the number of voices I could fit on a chip. All ENSONIQ sound chips use a multiplexed oscillator which allows us to produce at least 32 voices per chip. Aside from that, little else of SID is to be found in our designs, which more closely resemble the Mountain Computer sound card for the Apple II (the basis of the Alpha Syntauri system). The DOC I chip (used in the Mirage and ESQ-1) was modeled on this sound card. Our current designs, which include waveform interpolation, digital filters and digital effects are new designs that aren't really based on anything other than our imaginations.” > “The issue wasn't budget, it was development time and chip size constraints. The design/prototype/debug/production schedule of the SID chip, VIC II chip and Commodore 64 were incredibly tight (some would say impossibly tight)--we did things faster than Commodore had ever done before and were never able to repeat after! If I had had more time, I would have developed a proper MOS op-amp which would have eliminated the signal leakage which occurred when the volume of the voice was supposed to be zero. This lead to poor signal-to-noise ratio, although it could be dealt with by stopping the oscillator. It would also have greatly improved the filter, particularly in achieving high resonance. I originally planned to have an exponential look-up table to provide a direct translation for the equal-tempered scale, but it took up too much silicon and it was easy enough to do in software anyway.” https://web.archive.org/web/20070222065716/http://stud1.tuwien.ac.at/~e9426444/yannes.html https://web.archive.org/web/20070222065716/http://stud1.tuwi... https://en.wikipedia.org/wiki/Bob_Yannes https://en.wikipedia.org/wiki/Bob_Yannes https://en.wikipedia.org/wiki/Ensoniq https://en.wikipedia.org/wiki/Ensoniq
Mountain_Skies 3y ago
Makes me wonder if the output could have been used as part of a better random number generator on the 64.
- classichasclass 3y ago
  As it happens, you can snoop on the output of voice 3, and in noise mode it could indeed be used for random numbers. It generates a new value about every 26 processor cycles.

WalterSear 3y ago

It's a partially analog circuit.

radarsat1 3y ago
Yeah, exactly. So I was wondering of the same analog circuit has been built outside an IC (ie. discrete components) but according to the other response, the IC specifics are integral to the result, which is crazy and really cool.
- exDM69 3y ago
  The original chip was built with 1970s NMOS semiconductor technology. While you can theoretically build the same analog circuitry using discrete N-channel MOSFETs, it will not capture the tone of the original. In particular the "operational amplifiers" used in the design were very simplistic things built out of just a handful of transistors and are very non-linear devices. It is possible to build a circuit that behaves similarly but it won't sound the same.