ctr lists that "Sound driver implementations and/or converters" are not allowed so I am not sure if this submission is valid.
Yeah, we have rejected submissions using converters in the past (for example,
Great Sluggers). While I don't mind that the VGMs are made in the first place, they should be treated as "unofficial submissions" and posted in the Homebrew forum.
For official submissions, we want to log the music from the original code as much as possible. Converting between chips can be done as long as it done during logging (for example a modified MAME build that logs DAC as YM2612). Converting directly from sound data should be avoided. Ideally, support for the C15 (and other WSG) chips should be added to the VGM spec, but we've been in a feature-freeze due to the libvgm rewrite. That is pretty much done now, so I suppose it could happen if the interest is there.
The conversion sounds very truthful to the original but the volume ramping in C352 introduces smooth transitions between volume levels and affects the "sharpness" of some of the sounds. ctr's C352 emulation from QuattroPlay allows for setting the C352_FLG_FILTER flag disabling that effect (which is included in the tracks btw.) but that is not implemented in any of the official VGM players.
This behavior has not at all been verified on a real chip, so relying on it (in a converter) might also be problematic.
The list includes many short sound effects which are not particularly exciting to listen to so, in my opinion, the pack could be cut down to musical tracks only. Or there could be two separate packs: full, ost only.
For official submissions, we usually only include music and jingles. But for an unofficial pack, anything goes.
The songs are extracted using my own reverse-engineered music driver/interpreter and validated against the register dumps from Mame. .... I have written a wsg2c352 converter based on the ideas from the ctr's QuattroPlay.
I'd be interested in looking at the converter. I would definitely be open to adding support for earlier games in QuattroPlay but it hasn't been done mostly due to lack of time to do the necessary research / reverse engineering.