SID3

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Synth Channel Features

• Two phase accumulator based oscillators: One for tone and one for noise LFSR clocking
  • Frequency range: 0.001Hz to ~15kHz at default clock speed
• 5 waveform types (can be enabled in any combination):
  • Pulse (with 16-bit pulse width control)
  • Triangle
  • Sawtooth
  • Noise
  • Special wave (58 different types including all OPL3 and OPZ waveforms, their clipped versions, cubed variations, and more)
• Noise generation: From 30-bit LFSR
  • Like C64, eight bits form 8-bit noise signal
  • Adjustable feedback (any bit can be feedback bit)
  • Some configurations produce tonal noise that Furnace automatically detects and tunes
  • 1-bit noise mode available for AY-style noise
• 5 waveform mixing modes:
  • 8580 SID (combined waves; bitwise AND with noise and special wave)
  • Bitwise AND
  • Bitwise OR
  • Bitwise XOR
  • Sum of oscillators’ signals
• Hard sync: Each channel can have any other channel as sync source (even itself)
• Ring modulation: Each channel can have any other channel as modulation source (even itself)
  • Self-modulation effectively squares the signal
• Phase modulation: Each channel can have any other channel as modulation source (even itself)
  • Self-modulation creates feedback-like effect
  • Channel output after filters is used as modulation source
• ADSR envelope with sustain rate setting (decay speed during sustain phase)
• 4 independent filters:
  • Each filter has its own cutoff, resonance, output volume, mode, on/off, and distortion
  • Can be connected to channel’s ADSR output
  • Output can be routed to final channel output
  • Full connection matrix between filter outputs and inputs
  • Distortion: Asymmetrical with hyperbolic tangent (positive) and exponential (negative)
  • Filters can be chained for flexible subtractive synthesis or increased slope (12 dB/octave per filter)
  • Multiple modes can be selected simultaneously (e.g., low+high = bandstop/notch)
• Adjustable feedback: Saves two previous outputs and adds them to accumulator before computing waveform
• Fine stereo panning control
• Channel inversion: Left and right signals can be inverted for “surround” sound

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Wave Channel

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Effects

• 1xxx: Set filter 1 cutoff (range: 000 to FFF)
• 2xxx: Set filter 2 cutoff (range: 000 to FFF)
• 3xxx: Set filter 3 cutoff (range: 000 to FFF)
• 4xxx: Set filter 4 cutoff (range: 000 to FFF)
• 5xxx: Set duty cycle (range: 000 to FFF)
• 60xx: Change wave (lower 5 bits)
  • Bit 0: Triangle
  • Bit 1: Saw
  • Bit 2: Pulse
  • Bit 3: Noise
  • Bit 4: Special wave
• 61xx: Change special wave (range: 00 to 39)
• 62xx: Modulation control (lower 3 bits)
  • Bit 0: Ring modulation
  • Bit 1: Oscillator sync
  • Bit 2: Phase modulation
• 63xy: Reset duty cycle
  • x ≠ 0: On new note
  • y ≠ 0: Now
• 64xx: Set ring modulation source channel (00 to 07, where 07 is self-modulation)
• 65xx: Set hard sync source channel (00 to 06)
• 66xx: Set phase modulation source channel (00 to 06)
• 67xx: Set attack (range: 00 to FF)
• 68xx: Set decay (range: 00 to FF)
• 69xx: Set sustain level (range: 00 to FF)
• 6Axx: Set sustain rate (range: 00 to FF)
• 6Bxx: Set release (range: 00 to FF)
• 6Cxx: Set waveform mix mode (range: 00 to 04)
• 6Dxx: Set noise LFSR feedback bits (low byte) (range: 00 to FF)
• 6Exx: Set noise LFSR feedback bits (medium byte) (range: 00 to FF)
• 6Fxx: Set noise LFSR feedback bits (high byte) (range: 00 to FF)
• 70xx: Set noise LFSR feedback bits (highest bits) (range: 00 to 3F)
• 71xx: Set filter 1 resonance (range: 00 to FF)
• 72xx: Set filter 2 resonance (range: 00 to FF)
• 73xx: Set filter 3 resonance (range: 00 to FF)
• 74xx: Set filter 4 resonance (range: 00 to FF)
• 75xx: Set noise/wave channel mode (range: 00 to 01)
  • Synth channels: 00 = normal noise, 01 = 1-bit noise
  • Wave channel: 00 = wavetable, 01 = streamed PCM sample
• 76xx: Set filter 1 output volume (range: 00 to FF)
• 77xx: Set filter 2 output volume (range: 00 to FF)
• 78xx: Set filter 3 output volume (range: 00 to FF)
• 79xx: Set filter 4 output volume (range: 00 to FF)
• 7Axx: Set filter 1 distortion (range: 00 to FF)
• 7Bxx: Set filter 2 distortion (range: 00 to FF)
• 7Cxx: Set filter 3 distortion (range: 00 to FF)
• 7Dxx: Set filter 4 distortion (range: 00 to FF)
• 7Exx: Set feedback (range: 00 to FF)
• 7Fxx: Channel inversion control (lower 2 bits)
  • Bit 0: Invert right channel
  • Bit 1: Invert left channel
• A0xy: Set filter mode
  • x: Filter number (0-3)
  • y (lower 3 bits):
    • Bit 0: Low pass
    • Bit 1: Band pass
    • Bit 2: High pass
• A1xy: Set filter connection
  • x: Filter number (0-3)
  • y (lower 2 bits):
    • Bit 0: Connect filter input to channel’s ADSR output
    • Bit 1: Connect filter output to final channel output
• A2xy: Set filter connection matrix row
  • x: Filter number (0-3)
  • y (lower 4 bits):
    • Bit 0: Connect to filter 1 output
    • Bit 1: Connect to filter 2 output
    • Bit 2: Connect to filter 3 output
    • Bit 3: Connect to filter 4 output
• A3xy: Enable filter
  • x: Filter number (0-3)
  • y: 0 (disabled) or 1 (enabled)
• A4xx: Pulse width slide up (xx is speed; A400 stops)
• A5xx: Pulse width slide down (xx is speed; A500 stops)
• A6xx: Filter 1 cutoff slide up (xx is speed; A600 stops)
• A7xx: Filter 1 cutoff slide down (xx is speed; A700 stops)
• A8xx: Filter 2 cutoff slide up (xx is speed; A800 stops)
• A9xx: Filter 2 cutoff slide down (xx is speed; A900 stops)
• AAxx: Filter 3 cutoff slide up (xx is speed; AA00 stops)
• ABxx: Filter 3 cutoff slide down (xx is speed; AB00 stops)
• ACxx: Filter 4 cutoff slide up (xx is speed; AC00 stops)
• ADxx: Filter 4 cutoff slide down (xx is speed; AD00 stops)
• AExx: Tone phase reset (xx is tick number)
• AFxx: Noise phase reset (xx is tick number)
• B0xx: Envelope reset (xx is tick number)
• B1xy: Filter cutoff scaling control
  • x: Filter number (0-3)
  • y (lower 2 bits):
    • Bit 0: Enable cutoff scaling
    • Bit 1: Inverse cutoff scaling
• B2xy: Filter resonance scaling control
  • x: Filter number (0-3)
  • y (lower 2 bits):
    • Bit 0: Enable resonance scaling
    • Bit 1: Inverse resonance scaling

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Chip Configuration

• Lowers CPU load almost 4 times
• Filters may become unstable or have different timbre at high cutoff/resonance
• Only affects playback mode; not applied when rendering to audio file