83 lines
2.4 KiB
Markdown
83 lines
2.4 KiB
Markdown
# Audio-Rate Modulation
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Any parameter can be modulated continuously using modulation words. Instead of a fixed value, these words produce a modulation string that the engine interprets as a moving signal.
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All time values are in **steps**, just like `attack`, `decay`, and `release`. At 120 BPM with speed 1, one step is 0.125 seconds. Writing `4 lfo` means a 4-step period.
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## LFOs
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Oscillate a parameter between two values.
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```forth
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saw s 200 4000 4 lfo lpf . ( sweep filter over 4 steps )
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saw s 0.3 0.7 2 tlfo pan . ( triangle pan over 2 steps )
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```
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| Word | Shape | Output |
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|------|-------|--------|
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| `lfo` | Sine | `min~max:period` |
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| `tlfo` | Triangle | `min~max:periodt` |
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| `wlfo` | Sawtooth | `min~max:periodw` |
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| `qlfo` | Square | `min~max:periodq` |
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Stack effect: `( min max period -- str )`
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## Slides
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Transition from one value to another over a duration.
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```forth
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saw s 0 1 0.5 slide gain . ( fade in over half a step )
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saw s 200 4000 8 sslide lpf . ( smooth sweep over 8 steps )
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```
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| Word | Curve | Output |
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|------|-------|--------|
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| `slide` | Linear | `start>end:dur` |
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| `expslide` | Exponential | `start>end:dure` |
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| `sslide` | Smooth (S-curve) | `start>end:durs` |
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Stack effect: `( start end dur -- str )`
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## Random
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Randomize a parameter within a range, retriggering at a given period.
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```forth
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saw s 200 4000 2 jit lpf . ( new random value every 2 steps )
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saw s 200 4000 2 sjit lpf . ( same but smoothly interpolated )
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saw s 200 4000 1 drunk lpf . ( random walk, each step )
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```
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| Word | Behavior | Output |
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|------|----------|--------|
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| `jit` | Sample & hold | `min?max:period` |
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| `sjit` | Smooth interpolation | `min?max:periods` |
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| `drunk` | Random walk | `min?max:periodd` |
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Stack effect: `( min max period -- str )`
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## Envelopes
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Define a multi-segment envelope for a parameter. Provide a start value, then pairs of target and duration.
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```forth
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saw s 0 1 0.1 0.7 0.5 0 8 env gain .
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```
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This creates: start at `0`, rise to `1` in `0.1` steps, drop to `0.7` in `0.5` steps, fall to `0` in `8` steps.
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Stack effect: `( start target1 dur1 [target2 dur2 ...] -- str )`
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## Combining
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Modulation words return strings, so they compose naturally with the rest of the language. Use them anywhere a parameter value is expected.
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```forth
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saw s
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200 4000 4 lfo lpf
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0.3 0.7 8 tlfo pan
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0 1 0.1 0.7 0.5 0 8 env gain
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.
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```
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