3 ms·

Waveform tables are still usually stored as a 2^n bytes, where n is a relatively small number. The rate is changed by resampling. So this was a known and standa

Waveform tables are still usually stored as a 2^n bytes, where n is a relatively small number. The rate is changed by resampling. So this was a known and standard digital synthesis technique, even then. The clever part is the log arithmetic and the use of symmetry. The really clever part is doing it in custom ICs. Yamaha already had custom ICs in its organs and analogue synths, but I still don't know who taped out and then fabbed a relatively state of the art digital design in 1983. Someone in management decided to make a huge investment in the DX line, and it paid off. Imagine if the project had bombed and the company was left with a couple of hundred thousand unwanted chips. But the whole project was a triumph. It wasn't just outstanding engineering, it was a very ballsy business move.

jacquesm 5y ago
Spot on, this must have been an enormous gamble, because it is not one but two of these 64 pin monsters. Unfortunately the other one (which I've already desoldered, it's lying right in front of me) is cast in plastic rather than with a removable lid so it will take some more magic to get that one to give up its secrets.
- djmips 5y ago
  There's always this technique perhaps. https://www.youtube.com/watch?v=ZQeHHYJYWXo https://www.youtube.com/watch?v=ZQeHHYJYWXo
  - jacquesm 5y ago
    Very interesting, but this is a pretty unique chip and I would definitely not risk it on a coarse method like that. But if I had a bunch of them I would probably try it on one or two.
    - wdfx 5y ago
      One thing I keep thinking when I read of how yourself and Ken (and others) reverse engineer these chips... Are these devices and chips still plentiful enough to justify destroying them for this purpose? I'm sorry if that sounds like a harsh criticism, I don't intend it that way and I'm genuinely curious regarding how you and others doing similar things with these vintage chips weigh up the pros and cons of going through with the disassembly of any particular example. I find these articles fascinating and hope to continue learning from the content. But I can't help but think that should these devices be celebrated by actually using them rather than tearing them apart?
      - jacquesm 5y ago
        Your concern is 100% valid. The chip that I sent to Ken came from a DX7 motherboard that had seen an extremely rough life and at least one other critical chip on that board was dead. The EGS and OPS are nigh on indestructible, I've seen my share of these by now and they always work, no matter what the state of the rest of the board. So, figuring that no matter what happens to that board that I will always end up with at least one surplus set of EGS/OPS chips even though they are still good it wasn't a huge decision to sacrifice them, the potential for knowledge gained far outweighs the value of these chips. I repair DX7's to keep them 'in play', it doesn't really make me any money but it feels good to spend my spare time on getting one of these oldies to 'good as new' state and then to see another super happy musician leave. The stuff I get in return comes in all kinds of states, from still somewhat working to completely dead. I usually have enough spares on hand to quickly swap out some big subsystems to figure out what's broken and then zoom in on the details. Afterwards, a complete disassembly, contact alignment (very critical), aftertouch bar check, cleaning, reassembly and testing, fresh battery and another one good to go. You can do one in a day or so once you get the hang of it. The particular board that these chips came out of had me initially entirely stumped. None of my usual revival tricks worked. After swapping out the CPU with a very rare working spare it was clear that it was never going to work again, CPU mysteriously dead. So it had been sitting in my parts bin for the last couple of years when Anthony contacted me and we started talking about his - and mine - DX7 ROM disassembly adventures. I had spent a lot of time on it a while ago, then moved on to making more music rather than working on yet more programming projects. He talked about the degree of certainty that people have about the insides of the OPS and EGS chips, which prompted me to contact Ken to ask if he would like to have a shot at working with one of these and he happily accepted. Which put the otherwise dust gathering chips to some good use. So, that's the story behind these chips, in short: no DX7s were harmed in the process of making these posts and hopefully the Gods of Silicon will forgive me the sacrifice made for the potential improvements made to software emulators as well as Anthony's disassembly project, which may well spring a generation of custom ROMS.
        wdfx 5y ago
        Thanks for the reply - I assumed that was the case, that these particular parts are now completely surplus and there's not enough of the remains of other units to make up anything functional. I agree also that there's benefits in documenting these for emulation and educational purposes.

jacquesm 5y ago

Spot on, this must have been an enormous gamble, because it is not one but two of these 64 pin monsters. Unfortunately the other one (which I've already desoldered, it's lying right in front of me) is cast in plastic rather than with a removable lid so it will take some more magic to get that one to give up its secrets.

djmips 5y ago
There's always this technique perhaps. https://www.youtube.com/watch?v=ZQeHHYJYWXo https://www.youtube.com/watch?v=ZQeHHYJYWXo
- jacquesm 5y ago
  Very interesting, but this is a pretty unique chip and I would definitely not risk it on a coarse method like that. But if I had a bunch of them I would probably try it on one or two.
  - wdfx 5y ago
    One thing I keep thinking when I read of how yourself and Ken (and others) reverse engineer these chips... Are these devices and chips still plentiful enough to justify destroying them for this purpose? I'm sorry if that sounds like a harsh criticism, I don't intend it that way and I'm genuinely curious regarding how you and others doing similar things with these vintage chips weigh up the pros and cons of going through with the disassembly of any particular example. I find these articles fascinating and hope to continue learning from the content. But I can't help but think that should these devices be celebrated by actually using them rather than tearing them apart?
    - jacquesm 5y ago
      Your concern is 100% valid. The chip that I sent to Ken came from a DX7 motherboard that had seen an extremely rough life and at least one other critical chip on that board was dead. The EGS and OPS are nigh on indestructible, I've seen my share of these by now and they always work, no matter what the state of the rest of the board. So, figuring that no matter what happens to that board that I will always end up with at least one surplus set of EGS/OPS chips even though they are still good it wasn't a huge decision to sacrifice them, the potential for knowledge gained far outweighs the value of these chips. I repair DX7's to keep them 'in play', it doesn't really make me any money but it feels good to spend my spare time on getting one of these oldies to 'good as new' state and then to see another super happy musician leave. The stuff I get in return comes in all kinds of states, from still somewhat working to completely dead. I usually have enough spares on hand to quickly swap out some big subsystems to figure out what's broken and then zoom in on the details. Afterwards, a complete disassembly, contact alignment (very critical), aftertouch bar check, cleaning, reassembly and testing, fresh battery and another one good to go. You can do one in a day or so once you get the hang of it. The particular board that these chips came out of had me initially entirely stumped. None of my usual revival tricks worked. After swapping out the CPU with a very rare working spare it was clear that it was never going to work again, CPU mysteriously dead. So it had been sitting in my parts bin for the last couple of years when Anthony contacted me and we started talking about his - and mine - DX7 ROM disassembly adventures. I had spent a lot of time on it a while ago, then moved on to making more music rather than working on yet more programming projects. He talked about the degree of certainty that people have about the insides of the OPS and EGS chips, which prompted me to contact Ken to ask if he would like to have a shot at working with one of these and he happily accepted. Which put the otherwise dust gathering chips to some good use. So, that's the story behind these chips, in short: no DX7s were harmed in the process of making these posts and hopefully the Gods of Silicon will forgive me the sacrifice made for the potential improvements made to software emulators as well as Anthony's disassembly project, which may well spring a generation of custom ROMS.
      - wdfx 5y ago
        Thanks for the reply - I assumed that was the case, that these particular parts are now completely surplus and there's not enough of the remains of other units to make up anything functional. I agree also that there's benefits in documenting these for emulation and educational purposes.