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Fixing a 30-year-old Roland synthesizer bug

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Re: Fixing a 30-year-old Roland synthesizer bug

#21

Post by rob74 »

montag wrote: post #15
digitailor wrote: post #2

This is cool, so TL;DR: The 3rd gen run of a Roland early digital synth product had an unresolved timing issue causing pitch playback problems. Recently, investigation revealed they hadn’t accounted for an Intel MCU part sub. The spec indicated the sub part was running too fast. They downclocked it via crystal swap which destroyed the unit’s MIDI timing. So they located the control ROM instructions to modify to fix t…

Yes, I love that the entire fix is a 5 byte change.

...plus the quartz crystal that you need to swap. And to get those 5 bytes into the ROM, you have to desolder that too unfortunately. But yeah, still cool.

Re: Fixing a 30-year-old Roland synthesizer bug

#22

Post by user5678 »

digitailor wrote: post #20
djmips wrote: post #18

Earlier quoted context omitted.

It wasn't pitch playback problems it was vibrato rate.

I get what you mean, it was a temporal issue, but it’s a PCM synth. That’s sample playback, and vibrato in that context is a modulation of pitch of sample playback over time. It’s a pitch playback problem that was caused by too fast a clock causing too fast a pitch playback modulation. (The LFO being used to produce the vibrato effect being misclocked due to too-fast MCU, causing a pitch playback problem. The pitch p…

No post body was provided.

Re: Fixing a 30-year-old Roland synthesizer bug

#23

Post by CamperBob2 »

ajxs wrote: post #3

Awesome work! I love the care and attention that people put into understanding these devices. I'm currently in the middle of a vintage synthesiser hacking project as well. Last year I made a fully annotated disassembly of the Yamaha DX7 firmware, and did some other technical analysis of the synth. Since then, I've been waiting for a chance to put this knowledge to good use. I found a DX9 on a local trading site, and…

Last year I made a fully annotated disassembly of the Yamaha DX7 firmware

Jesus.

Re: Fixing a 30-year-old Roland synthesizer bug

#24

Post by squarefoot »

digitailor wrote: post #8
pinewurst wrote: post #4

The Kawai K5 I used to have was also 8096 based.

Didn’t know that: hard to believe they managed to pull off additive synthesis on an 8096. That’s impressive I had a later Kawai K5000 which added short PCM samples for attack transients. That thing was crazy, foolishly gave it away more than a decade ago

I also had a K5000 and was so stupid to sell it over a decade ago; no way to find one again now at less than 5 times that money.

Re: Fixing a 30-year-old Roland synthesizer bug

#25

Post by ajxs »

thewebcount wrote: post #16
ajxs wrote: post #3

Awesome work! I love the care and attention that people put into understanding these devices. I'm currently in the middle of a vintage synthesiser hacking project as well. Last year I made a fully annotated disassembly of the Yamaha DX7 firmware, and did some other technical analysis of the synth. Since then, I've been waiting for a chance to put this knowledge to good use. I found a DX9 on a local trading site, and…

Are you familiar with Dexed[0]? It’s a free, open source DX7 emulator for most major DAWs. They’ve done similar work in figuring out how the device works internally. [0] https://asb2m10.github.io/dexed/

Yes, both Dexed, and its authors were a great source of help and information for me in my research on the DX7!

Re: Fixing a 30-year-old Roland synthesizer bug

#26

Post by ajxs »

NexRebular wrote: post #14
ajxs wrote: post #3

Awesome work! I love the care and attention that people put into understanding these devices. I'm currently in the middle of a vintage synthesiser hacking project as well. Last year I made a fully annotated disassembly of the Yamaha DX7 firmware, and did some other technical analysis of the synth. Since then, I've been waiting for a chance to put this knowledge to good use. I found a DX9 on a local trading site, and…

I wonder if DX100 firmware could be hacked like that as well, it being another of the 4-op beasts too

Unfortunately you can't add any more operators to the DX10, however you could probably add multitimbrality! Yamaha's YM2164 sound chip at the heart of the DX100 is pretty well understood, and very similar to the later YM2414 used in the multitimbral TX81Z.

Re: Fixing a 30-year-old Roland synthesizer bug

#27

Post by billforsternz »

ajxs wrote: post #3

Awesome work! I love the care and attention that people put into understanding these devices. I'm currently in the middle of a vintage synthesiser hacking project as well. Last year I made a fully annotated disassembly of the Yamaha DX7 firmware, and did some other technical analysis of the synth. Since then, I've been waiting for a chance to put this knowledge to good use. I found a DX9 on a local trading site, and…

I browsed through the repository as discovered by colejohnson66 downthread https://github.com/ajxs/yamaha_dx7_rom_disassembly. This is an example of superb, meticulous, lovingly documented work. The kind of thing you don't see every day, congratulations. The attention to detail is really just chef's kiss, starting with a really good repository name (a small thing, but still), continuing through clear and apparently comprehensive documentation of what you did and why, then on to beautifully formatted and commented assembly language (much better than the original source code I'd wager) with coherent and consistent paragraph commenting a particular delight, and finally (and very importantly) dedication to making sure others can reproduce your results and generate a matching binary too. There are likely to be other things of beauty in there I have forgotten to highlight, it's just that good. Oh the FAQ of course, what a great FAQ. Really I am being very wordy for someone that's lost for words.

BTW, I love retro computing too, this is my best attempt so far in the field https://github.com/billforsternz/retro-sargon. I aspire to similar standards to your good self, but I'm not there yet.

Re: Fixing a 30-year-old Roland synthesizer bug

#28

Post by avip »

ajxs wrote: post #3

Awesome work! I love the care and attention that people put into understanding these devices. I'm currently in the middle of a vintage synthesiser hacking project as well. Last year I made a fully annotated disassembly of the Yamaha DX7 firmware, and did some other technical analysis of the synth. Since then, I've been waiting for a chance to put this knowledge to good use. I found a DX9 on a local trading site, and…

Such clean and well organized work I rarely see. Painfully, I have to switch back now to my dayjob IDE.

Re: Fixing a 30-year-old Roland synthesizer bug

#29

Post by dep_b »

There's also a cool story about somebody fixing some bugs on the Six~Trak and related synthesizers by Sequential that were among the first MIDI synthesizers:

http://www.tauntek.com/SixTrackBug.htm

Though some bugs are really part of the sound now in my opinion. I bought a DX11 to replace my DX27S but I discovered it doesn't glitch as nice and now I need to keep both.

Re: Fixing a 30-year-old Roland synthesizer bug

#30

Post by tgv »

ajxs wrote: post #3

Awesome work! I love the care and attention that people put into understanding these devices. I'm currently in the middle of a vintage synthesiser hacking project as well. Last year I made a fully annotated disassembly of the Yamaha DX7 firmware, and did some other technical analysis of the synth. Since then, I've been waiting for a chance to put this knowledge to good use. I found a DX9 on a local trading site, and…

Are you telling me the DX9, my first synth all those years ago, actually had more than 4 operators?

BTW, another thing that made it less popular: its keyboard. It didn't have velocity sensitity, nor aftertouch. Or is that also a ROM-upgrade away?

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