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furnace/doc/4-instrument/sid2.md

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SID2 instrument editor

the SID2 instrument editor consists of two tabs: "SID2" to control various parameters of sound channels, and "Macros" containing several macros.

SID2

  • Waveform: allows selecting a waveform.

    • more than one waveform can be selected at once. in that case a logical AND mix of waves will occur...
      • although with default mix mode it does occur a bit wrong (like on 8580 SID chip). see below what happens when other modes are in use.
    • noise is an exception. it cannot be used with any of the other waveforms.
      • again, only when default mix mode is on.

  • Attack: determines the rising time for the sound. the bigger the value, the slower the attack. (0 to 15).

  • Decay: determines the diminishing time for the sound. the higher the value, the longer the decay (0 to 15).

  • Sustain: sets the volume level at which the sound stops decaying and holds steady (0 to 15).

  • Release: determines the rate at which the sound fades out after note off. the higher the value, the longer the release (0 to 15).

  • Duty: specifies the width of a pulse wave (0 to 4095).

  • Reset duty on new note: overwrite current duty value with the one that's specified in the instrument on new note.

  • Ring Modulation: when enabled, the channel's output will be multiplied with the previous channel's.

  • Oscillator Sync: enables oscillator hard sync. as the previous channel's oscillator finishes a cycle, it resets the period of the channel's oscillator, forcing the latter to have the same base frequency. this can produce a harmonically rich sound, the timbre of which can be altered by varying the synchronized oscillator's frequency.

  • Enable filter: when enabled, this instrument will go through the filter.

  • Initialize filter: initializes the filter with the specified parameters:

    • Cutoff: the filter's point in where frequencies are cut off (0 to 4095).
    • Resonance: amplifies or focuses on the cutoff frequency, creating a secondary peak forms and colors the original pitch (0 to 255).
    • Filter mode: sets the filter mode. you may pick one or more of the following:
      • low: a low-pass filter. the lower the cutoff, the darker the sound.
      • high: a high-pass filter. higher cutoff values result in a less "bassy" sound.
      • band: a band-pass filter. cutoff determines which part of the sound is heard (from bass to treble).
      • multiple filter modes can be selected simultaneously. for example, selecting both "low" and "high" results in a bandstop (notch) filter.

  • Noise Mode: dictates how noise behaves.

    • 0 means usual "white" noise.
    • 1-3 provide different tonal waves (in other words, small excerpts of noise are looped, creating a wave with tonal sound). mode 1 provides more "pure" tonal sound while modes 2 and 3 provide harsh, rich sounds, which can be further modified by filtering them.
    • when only noise wave is enabled, frequency calculation is altered in a way that this noise wave stays in tune, so wave can freely be used to play actual music.

  • Wave Mix Mode: dictates how different waves on the same channel are mixed together.

    • mode 0 does it the same way as on 8580 SID chip.
    • mode 1 does a bitwise AND between all the enabled waves (including noise!).
    • modes 2 and 3 operate in the same way, but they do bitwise OR and bitwise XOR.

  • Absolute Cutoff Macro: when enabled, the cutoff macro will go from 0 to 4095, and it will be absolute (in other words, control the cutoff directly rather than being relative).

  • Absolute Duty Macro: when enabled, the duty macro will go from 0 to 4095.

Macros

  • Volume: volume sequence.
  • Arpeggio: pitch sequence.
  • Pitch: fine pitch.
  • Duty: pulse width sequence.
  • Waveform: select the waveform used by instrument.
  • Phase Reset: trigger restart of envelope.
  • Cutoff: filter cutoff.
  • Filter Mode: select the filter mode.
  • Filter Toggle: turns filter on and off.
  • Resonance: filter resonance sequence.
  • Special: ring and oscillator sync selector, as well as:
    • gate bit:
      • set (1): key on. if previous state was 0 it triggers envelope start/restart; if previous state was 1, it does nothing.
      • reset (0): key off. if previous state was 1 it triggers envelope release; if previous state was 0, it does nothing.
  • Attack: sets envelope attack speed.
    • if you modify attack speed when the envelope is in attack phase it immediately changes.
  • Decay: sets envelope decay speed.
    • if you modify decay speed when envelope is in decay phase it immediately changes.
  • Sustain: sets envelope sustain level.
    • if you modify sustain level when envelope is in sustain phase it immediately changes. note that, unlike SID chips, you can change sustain level in any direction (both 2->5 and 5->2 work and do not trigger envelope release).
  • Release: sets envelope release speed.
    • if you modify release speed when envelope is in release phase it immediately changes.
  • Noise Mode: select the noise mode.
  • Wave Mix: select the waveform mix mode.