ChanServ changed the topic of ##yamahasynths to: Channel dedicated to questions and discussion of Yamaha FM Synthesizer internals and corresponding REing. Discussion of synthesis methods similar to the Yamaha line of chips, Sound Blasters + clones, PCM chips like RF5C68, and CD theory of operation are also on-topic. Channel logs: https://freenode.irclog.whitequark.org/~h~yamahasynths
<andlabs>
the MD version is truly refined =P
<andlabs>
the game itslef is a refinement
<andlabs>
it's a mix of missions from the two computer games
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<ValleyBell>
The CM-32P used address + data line scrambling, so it wouldn't surprise me if the SC-55 would do the same.
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<myon98>
Sorry for not being relevant (not even hardware) but VSC used a primitive address-swapped and XOR-obfuscated 8-bit linear ROM, possibly even more pointless when everything is unscrambled in software beforehand
<myon98>
Of course I don't think its data is directly related to its hardware counterparts though because of performance reasons and given the general crappiness of VSC, for example many samples seem to be in its original tone when played back in 22050 Hz (default in older VSCs and many code paths in vsc.sys assume the default sampling rate to be that)
<superctr>
i did take a look at the roms now, and i think encryption is looking less likely. the addresses and data bits are definitely swapped, the exact pattern is not determined yet
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<superctr>
i'm pretty sure the samples are 4-bit ADPCM or similar though
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<ValleyBell>
CM-32P used logarithmic 8-bit Delta-PCM.
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<ValleyBell>
superctr: For the CM-32P I made a small tool for analyzing bit patterns. Maybe it could be useful.
<ValleyBell>
It works best when the addresses are already descrambled though.
<ValleyBell>
(though if 32-byte blocks are intact, it should work decently well)
<superctr>
sample format i'm not worrying about right now
<superctr>
it's the address descrambling. which i have no clue, i tried switching the bits exactly like the pinout of the PCM chip, that is maybe 50% correct
<ValleyBell>
yeah, with the CM-32P it was a fair bit simpler due to the ROM containing all the sample tables and instrument names as well.
<ValleyBell>
and those tables cause some very nice repeating patterns
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<Lord_Nightmare>
btw if anyone (superctr, ValleyBell, anyone else) wants to help get some skeletal implementation of the LA32 done, I think i figured out how the SIN and EXP ROM stuff works. those roms are not QUITE the same as the ones used on yamaha chips but i have a program to accurately generate both to match the decap
<Lord_Nightmare>
the EXP ROM uses a harold alles style linear interpolation setup which i need to finish implementing
<Lord_Nightmare>
i.e. storing the slope (really, delta vs the last sample) of the current sample in the low 4 bits, which means linear interpolation between samples can be done with one ROM read
<Lord_Nightmare>
alles did it in his 1980 paper to allow storing a sine wave as 1/2 of a wave in sign-magnitude format
<Lord_Nightmare>
in theory you might be able to store 1/4 of a wave like yamaha did but its trickier since you need to store the local slope at a point rather than the delta between this and the next sample
<superctr>
Namco does that for the software LFO in their sound driver (storing each sample in the waveform with the initial position and delta)
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<andlabs>
cr1901_modern: (not tweeting this reply publicly) as for DOS, I asked dan gookin if he'd be interested in a new version of DOS for Dummies if FreeDOS ever took off and he said yes, so ... get on it
<cr1901_modern>
andlabs: I don't use FreeDOS much anymore. It's a very noble FOSS attempt to solve an inherently difficult problem- DOS software is badly behaved. But I find I can crash software easily w/ FreeDOS still that works fine on PC/MSDOS
<cr1901_modern>
myon98: What is VSC?
<andlabs>
myon98/Lord_Nightmare/ValleyBell: would following board traces help?
<superctr>
andlabs, no need for that i think, we have service manuals with schematics
<superctr>
but of course when using a logic analyzer you have to find the traces that are important (address lines for instance when descramblng the addresses)
<andlabs>
yeah that's what I'm talking about though
<andlabs>
meh
<andlabs>
also what's the best Sound Canvas? with perfect backward compatibility with the original models and all possible voices / polyphony / effects built irght in
<andlabs>
Roland ED SC-D70?
<andlabs>
actually huh the Roland ED SC-8850 had more voices than that
<andlabs>
guh
<andlabs>
but it has a lower bitrate than the D70
<andlabs>
(which is the only 44100hz model apparently)
<andlabs>
also "However, compatibility with these units is flawed due to modifications made to the synthesis engine as well as improper mapping of older instruments. "
<andlabs>
why is this so hard, roland
<andlabs>
I'll just wait for the roland boutique sound canvas
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