OPAL instrument

OPAL is a two-operator FM synthesizer inspired by OPL-era PC sound hardware. Each instrument is monophonic. NullPerator can allocate up to three OPAL instruments, so use separate instrument slots when you need simultaneous OPAL voices.

General settings lead into two aligned operator columns.

Instrument settings

Field	Values	Default	Behaviour
ALGORITHM	1*2, 1+2	1*2	Serial FM (operator 1 modulates 2) or parallel/additive output.
DEEP TREM/VIB	Two bits	00	Global deep-tremolo and deep-vibrato flags.
FEEDBACK	0–7	0	Feedback amount for operator 1.

For DEEP TREM/VIB, hold Enter, choose the tremolo or vibrato bit with Left / Right, and toggle it with Up / Down.

Operator settings

The lower section shows operator 1 and operator 2 side by side. Up / Down moves by row. Left / Right without Enter switches operator columns; hold Enter while changing the selected operator's value.

Field	Values	OP1 default	OP2 default	Behaviour
LEVEL	00–3F	17	00	Output attenuation: 00 is loudest and 3F is quietest.
MULTIPLIER	0–F	1	1	Operator frequency multiplier.
A/D/S/R	Four hex digits	F1C8	F1D8	Attack, decay, sustain, and release.
SHAPE	Eight choices	SINE	SINE	SINE, HALF, ABS, PULS, EVEN, AB-E, SQR, or DSQR.
TR/VB/SU/KSR	Four bits	0000	0010	Tremolo, vibrato, sustained envelope, and key-rate scaling flags.
KEYSCALE	0, 1.5, 3, 6	1.5	0	Selects the displayed high-note attenuation curve.

A/D/S/R and TR/VB/SU/KSR are component fields: hold Enter, select a digit or bit with Left / Right, then edit it with Up / Down.

Voice behaviour

One OPAL instrument owns one synth channel. If the same instrument number is triggered by several tracker tracks, a later note replaces the earlier note. Allocate another OPAL slot for another simultaneous voice, up to the fixed pool limit of three.