I did an update of sound driver, you may want to include in Vol2.
+ Fixed some bug with pulse2 channel after sfx played.
Removed code that not used by Sonic_1_OST songs, such as instruments, tremolo, arpeggio,
and other unused effects.
Memory usage reduced from 256 to 128 bytes: area $700-$77F. (Area $780 - $7FD now unused).
ZP memory used only $FB-$FF. (in previous version was used: $5C,$5D, $61,$62,
$67,$68, $6A,$6B, $7E, $87, $8D, $F4-$F7, $F9,$FA - now you can use it for your purposes).
Reduced CPU usage.
Here's the source:https://yadi.sk/d/C8Nvyx_ds4ygqQ
( put file "Sonic The Hedgehog (NES) Improvement V1.0 + Music Hack.nes" into folder and run build.bat )
Maybe you also want to make SFX that sounds more close to MD version,
then ask someone to create it in famitracker or any other editor or any rom. And after send it to me - I will convert to driver sfx format. The only limitation is to use single channel: pulse2 (square2), trianle or noise.