furnace/papers/doc/7-systems/soundunit.md

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# tildearrow Sound Unit
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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)
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# effects
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- `10xx`: set waveform
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- 0: pulse wave
- 1: sawtooth
- 2: sine wave
- 3: triangle wave
- 4: noise
- 5: periodic noise
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- 6: XOR sine
- 7: XOR triangle
- `12xx`: set pulse width (0 to 7F)
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- `13xx`: set resonance of filter (0 to FF)
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- despite what the internal effects list says (0 to F), you can use a resonance value from 0 to FF (255)
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- `14xx`: set filter mode and ringmod
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- bit 0: ring mod
- bit 1: low pass
- bit 2: high pass
- bit 3: band pass
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- `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
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- `1Axx`: set cutoff sweep period high byte
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- `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
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- bit 0-6: speed
- bit 7: up direction
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- `21xx`: toggle volume sweep
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- bit 0-4: speed
- bit 5: up direction
- bit 6: loop
- bit 7: alternate
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- `22xx`: toggle cutoff sweep
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- bit 0-6: speed
- bit 7: up direction
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- `4xxx`: set cutoff (0 to FFF)