indeed, very nice project!

I wonder, anyone with more in-depth knowledge, please, do give ideas - is it possible some simple digital captures from SC-88 with modification @esher made, to be done, which can answer how the ROM samples are processed, because currently to make them sound "properly" not once, but twice in a row RIAA filter is applied, I commented that many times, I believe one of the last times was here:

Re: About Roland Virtual Sound Canvas 3

which I find very strange and I even doubt is correct and what the real hardware is doing.

Also, same question about MT-32, i.e. simple digital captures made with @esher modification that can help evaluate how close the existing emulator is to the real thing, i.e. evaluate how precise is the emulator, any ideas how exactly such test could be performed?

I think that there will be no "digital reference sound" since the final mix in original MT32 is done in analog. Also i think that because of analog mixing, some sound artifacts were hidden behind the op-amp.
But i'll try different ways of digital mixing and interleaving to get as close as possible to "analog reference".

As for Roland SC series, the mod is the cleanest way to get digital reference, as all mixings are done before the DAC.

interesting! great work!
although analog has it's charms with it's noise floor (depending on person that is) having option for super clean sound is always welcome!

esher wrote on 2023-02-09, 11:51:

As for Roland SC series, the mod is the cleanest way to get digital reference, as all mixings are done before the DAC.

any idea, which sound, etc is best to be captured? I mean we have all the sounds from the ROM, I posted SC-88 descrambling code here:

Re: About Roland Virtual Sound Canvas 3

and my question is how best we use digital capture, i.e. what note, without any effects applied, etc to get any idea how the ROM samples are processed. I am not expert on synths and that's why I hope my questions is not that unclear. basically, with @esher excellent mod and ability to digitally capture, how we can figure out how to process the ROM sounds in the right way and not how at the moment emulators like this one:

https://github.com/skjelten/emusc

is doing it with the assumption (without any proof) of doing RIAA filtering 2 times in a row. I think using @esher digital mod to help proper emulator to be made is one of the best ways to preserve those excellent synths forever.

mattw wrote on 2023-02-09, 18:00:

any idea, which sound, etc is best to be captured? I mean we have all the sounds from the ROM, I posted SC-88 descrambling code […]
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any idea, which sound, etc is best to be captured? I mean we have all the sounds from the ROM, I posted SC-88 descrambling code here:

Re: About Roland Virtual Sound Canvas 3

and my question is how best we use digital capture, i.e. what note, without any effects applied, etc to get any idea how the ROM samples are processed. I am not expert on synths and that's why I hope my questions is not that unclear. basically, with @esher excellent mod and ability to digitally capture, how we can figure out how to process the ROM sounds in the right way and not how at the moment emulators like this one:

https://github.com/skjelten/emusc

is doing it with the assumption (without any proof) of doing RIAA filtering 2 times in a row. I think using @esher digital mod to help proper emulator to be made is one of the best ways to preserve those excellent synths forever.

i think the simplest sample is the best, e.g. square wave.

The SC mod is here https://github.com/vetal-esher/18bit-DIT, but people say that AK4103 is now obsolete and cannot be found anywhere. After finishing MT32-DIT mod, i'll return to 18bit-DIT rework, and may be
my verilog skills will improve and i'll make FPGA version without any DIT chip, just FPGA with all processing inside. Or, if i fail, there is always WM8804 cheap.

esher wrote on 2023-02-09, 19:41:

i think the simplest sample is the best, e.g. square wave.

yes, square wave (or sinus wave), make sense to me too. I found here "Square Wave" midi file for SC-88:

http://www.takuichi.net/hobby/edu/sonic_wave/ … nstrument/midi/

http://www.takuichi.net/hobby/edu/sonic_wave/ … /midi/pc081.mid

even I am not sure if it's the best midi file for such test, because it contains several notes, as far as I can tell when listen to it.

So, please, if you have the hardware make few such captures and post it here. in the mean time I will look at the ROMs and see how to "extract" the same sound(s) - that will allow comparison and I believe definitely can help and give some ideas.

I'll try to capture on Sunday, and there's no problem to record any note at any pitch. As a reference i think it is, no doubt, A4 which has clean 440Hz base.

mattw wrote on 2023-02-09, 23:28:

esher wrote on 2023-02-09, 19:41:

i think the simplest sample is the best, e.g. square wave.

yes, square wave (or sinus wave), make sense to me too. I found here "Square Wave" midi file for SC-88:

+1

Square waves make good harmonics in analogue circuits (audio, radio frequency).
So they're good candidates for testing filters.

esher wrote on 2023-02-10, 06:42:

I'll try to capture on Sunday, and there's no problem to record any note at any pitch. As a reference i think it is, no doubt, A4 which has clean 440Hz base.

thanks, from my side I used the code from here:

https://github.com/Kitrinx/SC55_Soundfont

to exact WAV from "square wave" instrument, it's supposed to be "E3" note and RIAA filtering is applied 2 times to it (the code can be patched and the filtering be removed, if that is necessary). Anyway, let we see with help from others here, if we can figure out what processing is applied to the original sample. I am attaching the file.

Here is the pc081.mid recorded via SC88 SPDIF: download/file.php?mode=view&id=157045
About E3 i tried record then realized that the default settings for square wave can be different on different devices (reverb, chorus, ADSR, etc), so the only way to be in equal conditions is recording the same midi.