[sdiy] Cheetah MS800 WAVE ROM craziness!

BrightBoy jdec at mindspring.com
Mon Jun 7 20:31:58 CEST 2021


When hacking waveform ROMs don't forget that sometimes the raw stored data has been 
bit re-ordered just to help with the layout of the PCB (think Roland TR-909)

Jeff

-----Original Message-----
From: Eric Brombaugh via Synth-diy synth-diy at synth-diy.org
Sent: Jun 7, 2021 2:08 PM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] Cheetah MS800 WAVE ROM craziness!


That's pretty cool stuff. It's interesting digging around in the music tech cellar like that - I've been helping someone reverse engineer the old Midiverb I and it's also full of all sorts of 1980s digital arcana. I'm to the point of having a Verilog model of the entire DSP section and trying to tease the secrets of the reverb algorithms out of the mess. It's slow going because of all the shortcuts they baked into the system to minimize the BOM.

On 6/7/21 10:42 AM, Richie Burnett wrote:
> For those interested in a bit of vintage equipment "hacking" I've read > both EPROMS from the Cheetah MS800 to raw binary files.  The 8Kbyte PROG > one has 6502 machine code in it.  The 32Kbyte WAVE EPROM is very strange > though...
> > When loaded into Goldwave as 8-bit signed data the first part of it > contains the MS800 wavetable waveform data in delta encoded format.  > This delta encoding is mentioned in the M114S datasheet, (the chip that > plays back the wave tables.)
> > Then there are some low-resolution *DRUM SAMPLES*, (cowbell, kick & > snare!) also delta encoded.  For example, the snare drum sample sounds > very TR-909 like when integrated and played back at 8kHz sample-rate!
> > I can't recall ever hearing my MS800 produce any drum sounds, but I > guess someone on the design team thought it was a good idea to put them > in there for some future or un-documented purpose.
> > The samples are then followed by a load of weird ASCII text in the > second half of the 32Kbyte address space.  Very strange considering the > MS800 only has a 2-digit 7-segment LED display!  Some of the ASCII text > follows...
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