133 lines
3.1 KiB
Markdown
133 lines
3.1 KiB
Markdown
# Modulation
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Modulation effects vary parameters over time using LFOs or envelopes.
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## Vibrato
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Vibrato modulates pitch with an LFO.
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```forth
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saw 5 vib 0.5 vibmod . ( 5 Hz, 0.5 semitone depth )
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```
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| Parameter | Range | Description |
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|-----------|-------|-------------|
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| `vib` | Hz | LFO rate |
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| `vibmod` | semitones | Modulation depth |
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| `vibshape` | shape | LFO waveform (sine, tri, saw, square) |
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## Pitch Envelope
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The pitch envelope applies an ADSR to the oscillator frequency.
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```forth
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sine 100 freq 24 penv 0.001 patt 0.1 pdec .
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```
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| Parameter | Description |
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|-----------|-------------|
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| `penv` | Envelope depth in semitones |
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| `patt` | Attack time in seconds |
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| `pdec` | Decay time in seconds |
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| `psus` | Sustain level (0-1) |
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| `prel` | Release time in seconds |
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## Glide
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Glide interpolates between pitch changes over time.
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```forth
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saw c4 0.1 glide . ( 100ms glide )
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```
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| Parameter | Range | Description |
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|-----------|-------|-------------|
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| `glide` | seconds | Glide time |
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## FM Synthesis
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FM modulates the carrier frequency with a modulator oscillator.
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```forth
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sine 440 freq 2 fm 2 fmh . ( modulator at 2× carrier frequency )
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```
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| Parameter | Range | Description |
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|-----------|-------|-------------|
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| `fm` | 0+ | Modulation index |
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| `fmh` | ratio | Harmonic ratio (modulator / carrier) |
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| `fmshape` | shape | Modulator waveform |
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FM has its own envelope (`fme`, `fma`, `fmd`, `fms`, `fmr`).
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## Amplitude Modulation
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AM multiplies the signal by an LFO.
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```forth
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pad 4 am 0.5 amdepth . ( 4 Hz tremolo )
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```
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| Parameter | Range | Description |
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|-----------|-------|-------------|
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| `am` | Hz | LFO rate |
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| `amdepth` | 0-1 | Modulation depth |
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| `amshape` | shape | LFO waveform |
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## Ring Modulation
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Ring modulation multiplies two signals, producing sum and difference frequencies.
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```forth
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saw 150 rm 0.8 rmdepth . ( ring mod at 150 Hz )
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```
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| Parameter | Range | Description |
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|-----------|-------|-------------|
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| `rm` | Hz | Modulator frequency |
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| `rmdepth` | 0-1 | Modulation depth |
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| `rmshape` | shape | Modulator waveform |
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## Phaser
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Phaser sweeps notches through the frequency spectrum using allpass filters.
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```forth
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pad 0.5 phaser 0.6 phaserdepth .
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```
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| Parameter | Range | Description |
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|-----------|-------|-------------|
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| `phaser` | Hz | Sweep rate |
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| `phaserdepth` | 0-1 | Sweep depth |
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| `phasersweep` | cents | Sweep range |
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| `phasercenter` | Hz | Center frequency |
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## Flanger
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Flanger mixes the signal with a short modulated delay (0.5-10ms).
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```forth
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pad 0.3 flanger 0.7 flangerdepth 0.5 flangerfeedback .
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```
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| Parameter | Range | Description |
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|-----------|-------|-------------|
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| `flanger` | Hz | Modulation rate |
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| `flangerdepth` | 0-1 | Modulation depth |
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| `flangerfeedback` | 0-0.95 | Feedback amount |
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## Chorus
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Chorus uses multiple modulated delay lines with 120° phase offset for stereo width.
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```forth
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pad 1 chorus 0.4 chorusdepth 20 chorusdelay .
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```
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| Parameter | Range | Description |
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|-----------|-------|-------------|
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| `chorus` | Hz | Modulation rate |
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| `chorusdepth` | 0-1 | Modulation depth |
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| `chorusdelay` | ms | Base delay time |
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