SonaPsg is the PSG instrument format in Sona. The recommended file
extension is ".spsg". PSG instruments are 8 bytes long:
uint8 ... total level (TL)
uint8 ... attack rate (AR)
uint8 ... sustain level (SL)
uint8 ... decay rate (DR)
uint8 ... sustain rate (SR)
uint8 ... release rate (SR)
uint8 ... reserved (must be 0)
uint8 ... reserved (must be 0)
AR, DR, SR, RR, TL and SL are equivalent to their YM2612 counterparts. All
values are measured in +0.125dB units. AR, DR, SR, RR indicate how much the
envelope advances every SFX tick (1/60th of a second*), while TL and SL are
the transition levels from AR to DR and from DR to SR.
ADSR values are volume, not attenuation. Higher values are louder.
* If the value of timer B is changed then the speed of ADSR envelopes will
also change.