This is meant to ["fix" games having unbalanced SFX vs the BGM](https://eadmaster.altervista.org/wordpress/archives/90). I've found the [`PSG::accumulateChannels()` in sound.cpp](https://github.com/libretro/gambatte-libretro/blob/master/libgambatte/src/sound.cpp#L96) may be the method to change, if you haven't better suggestions i'll try this myself. <bountysource-plugin> --- Want to back this issue? **[Post a bounty on it!](https://www.bountysource.com/issues/94603525-per-sound-channel-individual-volume-core-options-wip-help-needed?utm_campaign=plugin&utm_content=tracker%2F1258974&utm_medium=issues&utm_source=github)** We accept bounties via [Bountysource](https://www.bountysource.com/?utm_campaign=plugin&utm_content=tracker%2F1258974&utm_medium=issues&utm_source=github). </bountysource-plugin>