furnace/doc/4-instrument/fm-opl.md

OPL FM synthesis instrument editor

The OPL FM editor is divided into 7 tabs:

• FM: for controlling the basic parameters of FM sound source.
• Macros (FM): for macros controlling algorithm and feedback
• Macros (OP1): for macros controlling FM parameters of operator 1
• Macros (OP2): for macros controlling FM parameters of operator 2
• Macros (OP3): for macros controlling FM parameters of operator 3 (only when 4-op flag is set and only on OPL3!)
• Macros (OP4): for macros controlling FM parameters of operator 4 (only when 4-op flag is set and only on OPL3!)
• Macros: for miscellaneous macros controlling volume, arpeggio, and OPL3 panning.

FM

The OPL synthesizers are nominally two-operator (OPL3 supports 4-operator mode), meaning it takes two oscillators to produce a single sound.

These apply to the instrument as a whole:

• Feedback (FB): Determines how many times operator 1 returns its output to itself. (0-7 range)

• Algorithm (ALG): Determines how operators are connected to each other. (0-1 range and OPL1 and OPL2, 0-3 range on OPL3 4op mode)

  • Left-click pops up a small "operators changes with volume?" dialog where each operator can be toggled to scale with volume level.
  • Right-click to switch to a preview display of the waveform generated on a new note:
    • Left-click restarts the preview.
    • Middle-click pauses and unpauses the preview.
    • Right-click returns to algorithm view.

• 4-op: Enables 4-operator FM instrument editor mode (only on OPL3)

• Drums: Enables OPL drum mode editor

These apply to each operator:

• The crossed-arrows button can be dragged to rearrange operators.
• Amplitude Modulation (AM): Makes the operator affected by LFO tremolo.
• Sustain flag (SUS): When enabled, value of Sustain Level is in effect.
• Attack Rate (AR): determines the rising time for the sound. The bigger the value, the faster the attack. (0-15 range)
• Decay Rate (DR): Determines the diminishing time for the sound. The higher the value, the shorter the decay. It's the initial amplitude decay rate. (0-15 range)
• Sustain Level (SL): Determines the point at which the sound ceases to decay and changes to a sound having a constant level. The sustain level is expressed as a fraction of the maximum level. (0-15 range)
• Release Rate (RR): Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the shorter the release. (0-15 range)
• Total Level (TL): Represents the envelope’s highest amplitude, with 0 being the largest and 63 (decimal) the smallest. A change of one unit is about 0.75 dB.
• Key Scale Level (KSL): Also known as "Level Scale". Determines the degree to which the amplitude decreases according to the pitch.

• Key Scale Rate (KSR): Also known as "Rate Scale". Determines the degree to which the envelope execution speed increases according to the pitch.
• Frequency Multiplier (MULT): Determines the operator frequency in relation to the pitch. (0-15 range but be noted that 11, 13 and 14 have no effect!)
• Waveform Select (WS): Changes the waveform generated by oscillator (OPL2 and OPL3 only, 0-3 range on OPL2 and 0-7 on OPL3)
• Vibrato (VIB): Makes the operator affected by LFO vibrato.

macros

Macros define the sequence of values passed to the given parameter. Via macro, along with the previously mentioned parameters, the following can be controlled:

FM Macros

All parameters are listed above.

OP1-OP4 Macros

All parameters are listed above.

Macros

• Arpeggio: Pitch change sequence in semitones.
• Panning: toggles output on left and right channels. (OPL3 only!)
• Pitch: fine pitch.
  • Relative: pitch changes are relative to the current pitch, not the note's base pitch.
• Phase Reset: Restarts all operators and resets the waveform to its start. Effectively the same as a 0Cxx retrigger.