furnace/doc/7-systems/soundunit.md

tildearrow Sound Unit

a fantasy sound chip, used in the specs2 fantasy computer designed by tildearrow.

it has the following capabilities:

• 8 channels of either waveform or sample
• stereo sound
• 8 waveforms (pulse, saw, sine, triangle, noise, periodic noise, XOR sine and XOR triangle)
• 128 widths for the pulse wave
• per-channel resonant filter
• ring modulation
• volume, frequency and cutoff sweep units (per-channel)
• phase reset timer (per-channel)

effects

• 10xx: set waveform.
  • 0: pulse wave
  • 1: sawtooth
  • 2: sine wave
  • 3: triangle wave
  • 4: noise
  • 5: periodic noise
  • 6: XOR sine
  • 7: XOR triangle
• 12xx: set pulse width. range is 0 to 7F.
• 13xx: set resonance of filter. range is 0 to FF.
  • despite what the internal effects list says (0 to F), you can use a resonance value from 0 to FF (255).
• 14xx: set filter mode and ringmod.
  • bit 0: ring mod
  • bit 1: low pass
  • bit 2: high pass
  • bit 3: band pass
• 15xx: set frequency sweep period low byte.
• 16xx: set frequency sweep period high byte.
• 17xx: set volume sweep period low byte.
• 18xx: set volume sweep period high byte.
• 19xx: set cutoff sweep period low byte.
• 1Axx: set cutoff sweep period high byte.
• 1Bxx: set frequency sweep boundary.
• 1Cxx: set volume sweep boundary.
• 1Dxx: set cutoff sweep boundary.
• 1Exx: set phase reset period low byte.
• 1Fxx: set phase reset period high byte.
• 20xx: toggle frequency sweep.
  • bit 0-6: speed
  • bit 7: up direction
• 21xx: toggle volume sweep.
  • bit 0-4: speed
  • bit 5: up direction
  • bit 6: loop
  • bit 7: alternate
• 22xx: toggle cutoff sweep.
  • bit 0-6: speed
  • bit 7: up direction
• 4xxx: set cutoff. range is 0 to FFF.