Missing parameters KSR, KSL, EGTYP

[bryc]

I recently tried to port parameters of OPL2 to OPLL, which was made difficult or impossible for some reasons.

The primary issue is that vst2413 gives no access to chip parameters of KSR (Envelope Scaling), KSL (Level scaling) or EGTYP (Hold Sustain).

These missing parameters do affect sound, and sometimes help to improve approximations of OPN/OPM instruments converted to OPL. KSR can sometimes give more approximate ADSR timings, and KSL sometimes gives more approximate modulation of TL.

Please consider adding these parameters.

I also have a question. ADSR Sustain shows 0-45 dB, but chip parameter is only 0-15. It appears each value is duplicated 3 times. Is this intentional? This makes it hard to translate patch values from other software to vst2413, which use standard parameter integer display.