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docs/lfo.md

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+# LFO & Ramps
+
+Generate time-varying values synchronized to the beat for modulation.
+
+## Ramp
+
+The `ramp` word creates a sawtooth wave from 0 to 1:
+
+```forth
+0.25 1.0 ramp  ( one cycle per 4 beats, linear )
+1.0 2.0 ramp   ( one cycle per beat, exponential curve )
+```
+
+Stack: `(freq curve -- val)`
+
+## Shortcut Ramps
+
+```forth
+0.5 linramp   ( linear ramp, curve=1 )
+0.25 expramp  ( exponential ramp, curve=3 )
+2.0 logramp   ( logarithmic ramp, curve=0.3 )
+```
+
+## Triangle Wave
+
+```forth
+0.5 tri  ( triangle wave 0→1→0 )
+```
+
+## Perlin Noise
+
+Smooth random modulation:
+
+```forth
+0.25 perlin  ( smooth noise at 0.25x beat rate )
+```
+
+## Range Scaling
+
+Scale a 0-1 value to any range:
+
+```forth
+0.5 200 800 range  ( 0.5 becomes 500 )
+```
+
+## Examples
+
+Modulate filter cutoff:
+
+```forth
+"saw" s
+  0.25 1.0 ramp 500 2000 range lpf
+.
+```
+
+Random panning:
+
+```forth
+"hat" s
+  0.5 perlin -1 1 range pan
+.
+```
+
+## Words
+
+| Word | Stack | Description |
+|------|-------|-------------|
+| `ramp` | (freq curve -- val) | Ramp 0-1: fract(freq*beat)^curve |
+| `linramp` | (freq -- val) | Linear ramp (curve=1) |
+| `expramp` | (freq -- val) | Exponential ramp (curve=3) |
+| `logramp` | (freq -- val) | Logarithmic ramp (curve=0.3) |
+| `tri` | (freq -- val) | Triangle wave 0→1→0 |
+| `perlin` | (freq -- val) | Perlin noise 0-1 |
+| `range` | (val min max -- scaled) | Scale 0-1 to min-max |