Comment by digitailor | Hacker News Reader

Comment by digitailor | Hacker News Reader

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 the resulting MIDI sync issue and burned a new one:

  0x1A8D: 1D5Fh -> 1388h
  0x215C: 17h -> 0Fh
  0x216D: 1D5Fh -> 1388h

That’s it. Surgical.

I spent some time inside an early Roland sampler of this era during the pandemic. It’s really well engineered stuff that sounds great.

I guess it makes sense that it would be a common divider ratio (5000) but $1388 leapt out at me from disassembling the Ensoniq Mirage firmware.

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 playback modulation was at the wrong rate.)

Ah, relief. Big Roland fan but don’t have this particular piece of gear & had trouble following TFA

This reminds me of the binary patching done in The Martian film.

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.

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