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docs/engine_distortion.md

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+# Distortion
+
+Distortion effects add harmonics by nonlinearly shaping the waveform.
+
+## Saturation
+
+Soft saturation using the transfer function `x / (1 + k|x|)`.
+
+```forth
+saw 2 distort .
+saw 8 distort 0.5 distortvol .   ( with volume compensation )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `distort` | 0+ | Saturation amount |
+| `distortvol` | 0-1 | Output volume |
+
+## Wavefolding
+
+Wavefolding reflects the signal when it exceeds ±1, using `sin(x × amount × π/2)`.
+
+```forth
+sine 4 fold .
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `fold` | 0+ | Fold amount |
+
+## Wavewrapping
+
+Wavewrapping applies modulo to wrap the signal into the -1 to 1 range.
+
+```forth
+saw 3 wrap .
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `wrap` | 0+ | Number of wraps |
+
+## Bit Crushing
+
+Bit crushing quantizes the signal to fewer amplitude levels.
+
+```forth
+snare 6 crush .              ( 6-bit = 32 levels )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `crush` | 1-16 | Bit depth |
+
+## Sample Rate Reduction
+
+Sample rate reduction holds each sample for multiple output samples.
+
+```forth
+hat 4 coarse .               ( 1/4 effective sample rate )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `coarse` | 1+ | Reduction factor (1 = bypass) |

docs/engine_filters.md

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+# Filters
+
+Filters attenuate frequencies above or below a cutoff point.
+
+## Lowpass Filter
+
+The lowpass filter (`lpf`) attenuates frequencies above the cutoff.
+
+```forth
+saw 1000 lpf .               ( cut above 1000 Hz )
+saw 500 lpf 0.8 lpq .        ( with resonance )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `lpf` | Hz | Cutoff frequency |
+| `lpq` | 0-1 | Resonance (peak at cutoff) |
+
+## Highpass Filter
+
+The highpass filter (`hpf`) attenuates frequencies below the cutoff.
+
+```forth
+kick 200 hpf .               ( cut below 200 Hz )
+pad 400 hpf 0.3 hpq .        ( with resonance )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `hpf` | Hz | Cutoff frequency |
+| `hpq` | 0-1 | Resonance |
+
+## Bandpass Filter
+
+The bandpass filter (`bpf`) attenuates frequencies outside a band around the center frequency.
+
+```forth
+noise 1000 bpf 0.7 bpq .     ( narrow band around 1000 Hz )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `bpf` | Hz | Center frequency |
+| `bpq` | 0-1 | Resonance (narrower band) |
+
+## Filter Slope
+
+The `ftype` parameter sets the filter slope (rolloff steepness).
+
+| Value | Slope |
+|-------|-------|
+| `1` | 12 dB/octave |
+| `2` | 24 dB/octave (default) |
+| `3` | 48 dB/octave |
+
+```forth
+saw 800 lpf 3 ftype .        ( 48 dB/oct lowpass )
+```
+
+## Filter Envelope
+
+Filters can be modulated by an ADSR envelope. The envelope multiplies the base cutoff:
+
+```
+final_cutoff = lpf + (lpe × envelope × lpf)
+```
+
+When the envelope is at 1.0 and `lpe` is 1.0, the cutoff doubles. When the envelope is at 0, the cutoff equals `lpf`.
+
+```forth
+saw 200 lpf 2 lpe 0.01 lpa 0.3 lpd .   ( cutoff sweeps from 600 Hz down to 200 Hz )
+```
+
+| Parameter | Description |
+|-----------|-------------|
+| `lpe` | Envelope depth (multiplier, 1.0 = double cutoff at peak) |
+| `lpa` | Attack time in seconds |
+| `lpd` | Decay time in seconds |
+| `lps` | Sustain level (0-1) |
+| `lpr` | Release time in seconds |
+
+The same pattern works for highpass (`hpe`, `hpa`, etc.) and bandpass (`bpe`, `bpa`, etc.).
+
+## Ladder Filters
+
+Ladder filters use a different algorithm (Moog-style) with self-oscillation at high resonance.
+
+```forth
+saw 800 llpf 0.7 llpq .      ( ladder lowpass )
+saw 300 lhpf 0.5 lhpq .      ( ladder highpass )
+saw 1000 lbpf 0.8 lbpq .     ( ladder bandpass )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `llpf` | Hz | Ladder lowpass cutoff |
+| `llpq` | 0-1 | Ladder lowpass resonance |
+| `lhpf` | Hz | Ladder highpass cutoff |
+| `lhpq` | 0-1 | Ladder highpass resonance |
+| `lbpf` | Hz | Ladder bandpass cutoff |
+| `lbpq` | 0-1 | Ladder bandpass resonance |
+
+Ladder filters share the lowpass envelope parameters (`lpe`, `lpa`, etc.).
+
+## EQ
+
+The 3-band EQ applies shelf and peak filters at fixed frequencies.
+
+```forth
+kick 3 eqlo -2 eqhi .        ( +3 dB at 200 Hz, -2 dB at 5000 Hz )
+snare 2 eqmid .              ( +2 dB at 1000 Hz )
+```
+
+| Parameter | Frequency | Type |
+|-----------|-----------|------|
+| `eqlo` | 200 Hz | Low shelf (dB) |
+| `eqmid` | 1000 Hz | Peak (dB) |
+| `eqhi` | 5000 Hz | High shelf (dB) |
+
+## Tilt EQ
+
+Tilt EQ applies a high shelf at 800 Hz with up to ±6 dB gain.
+
+```forth
+pad -0.5 tilt .              ( -3 dB above 800 Hz )
+hat 0.5 tilt .               ( +3 dB above 800 Hz )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `tilt` | -1 to 1 | High shelf gain (-1 = -6 dB, 0 = flat, 1 = +6 dB) |

docs/engine_modulation.md

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

docs/engine_space.md

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+# Space & Time
+
+Spatial effects position sounds in the stereo field and add depth through delays and reverbs.
+
+## Pan
+
+Pan positions a sound in the stereo field.
+
+```forth
+hat -0.5 pan .               ( slightly left )
+perc 1 pan .                 ( hard right )
+kick 0 pan .                 ( center )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `pan` | -1 to 1 | Stereo position (-1 = left, 0 = center, 1 = right) |
+
+## Width
+
+Width controls the stereo spread using mid-side processing.
+
+```forth
+pad 1.5 width .              ( wider stereo )
+pad 0 width .                ( mono )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `width` | 0+ | Stereo width (0 = mono, 1 = unchanged, 2 = exaggerated) |
+
+## Haas Effect
+
+The Haas effect delays one channel slightly, creating a sense of stereo width and spatial placement.
+
+```forth
+snare 15 haas .              ( 15ms delay on right channel )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `haas` | ms | Delay time (1-10ms = subtle width, 10-35ms = distinct echo) |
+
+## Delay
+
+Delay is a send effect that creates echoes. The `delay` parameter sets how much signal is sent to the delay bus.
+
+```forth
+snare 0.3 delay 0.25 delaytime 0.5 delayfeedback .
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `delay` | 0-1 | Send level |
+| `delaytime` | seconds | Delay time |
+| `delayfeedback` | 0-0.95 | Feedback amount |
+| `delaytype` | type | Delay algorithm |
+
+### Delay Types
+
+| Type | Description |
+|------|-------------|
+| `standard` | Clean digital repeats |
+| `pingpong` | Bounces between left and right |
+| `tape` | Each repeat gets darker (analog warmth) |
+| `multitap` | 4 taps with swing control via feedback |
+
+```forth
+snare 0.4 delay pingpong delaytype .
+pad 0.3 delay tape delaytype .
+```
+
+## Reverb
+
+Reverb is a send effect that simulates acoustic spaces. The `verb` parameter sets the send level.
+
+```forth
+snare 0.2 verb 2 verbdecay .
+pad 0.4 verb 4 verbdecay 0.7 verbdamp .
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `verb` | 0-1 | Send level |
+| `verbdecay` | seconds | Reverb tail length |
+| `verbdamp` | 0-1 | High frequency damping |
+| `verbpredelay` | ms | Initial delay before reverb |
+| `verbdiff` | 0-1 | Diffusion (smears transients) |
+| `verbtype` | type | Reverb algorithm |
+
+### Reverb Types
+
+| Type | Description |
+|------|-------------|
+| `dattorro` | Plate reverb, bright and metallic shimmer |
+| `fdn` | Hall reverb, dense and smooth |
+
+```forth
+snare 0.3 verb dattorro verbtype .   ( plate )
+pad 0.5 verb fdn verbtype .          ( hall )
+```
+
+## Comb Filter
+
+The comb filter creates resonant pitched delays, useful for Karplus-Strong string synthesis and metallic tones.
+
+```forth
+white 0.5 comb 220 combfreq 0.9 combfeedback .   ( plucked string )
+```
+
+| Parameter | Range | Description |
+|-----------|-------|-------------|
+| `comb` | 0-1 | Send level |
+| `combfreq` | Hz | Resonant frequency |
+| `combfeedback` | 0-0.99 | Feedback (higher = longer decay) |
+| `combdamp` | 0-1 | High frequency damping |
+
+Higher feedback creates longer, ringing tones. Add damping for more natural string-like decay.

docs/engine_words.md

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+# Words & Sounds
+
+Word definitions let you abstract sound design into reusable units.
+
+## Defining Sounds
+
+```forth
+: lead "saw" s 0.3 gain 1200 lpf ;
+```
+
+Use it with different notes:
+
+```forth
+c4 note lead .
+e4 note lead .
+```
+
+## Self-Contained Words
+
+Include the emit to make the word play directly:
+
+```forth
+: kk "kick" s 1 decay . ;
+: hh "hihat" s 0.5 gain 0.5 decay . ;
+```
+
+Steps become simple:
+
+```forth
+kk
+0.5 at hh
+```
+
+## Effect Presets
+
+```forth
+: dark 800 lpf 0.6 lpq ;
+: wet 0.7 verb 8 verbdiff ;
+```
+
+```forth
+c4 note saw s dark wet .
+```

src/views/help_view.rs

@@ -48,6 +48,17 @@ const DOCS: &[DocEntry] = &[
     Topic("Sources", include_str!("../../docs/engine_sources.md")),
     Topic("Samples", include_str!("../../docs/engine_samples.md")),
     Topic("Wavetables", include_str!("../../docs/engine_wavetable.md")),
+    Topic("Filters", include_str!("../../docs/engine_filters.md")),
+    Topic(
+        "Modulation",
+        include_str!("../../docs/engine_modulation.md"),
+    ),
+    Topic(
+        "Distortion",
+        include_str!("../../docs/engine_distortion.md"),
+    ),
+    Topic("Space & Time", include_str!("../../docs/engine_space.md")),
+    Topic("Words & Sounds", include_str!("../../docs/engine_words.md")),
     // Reference
     Section("Reference"),
     Topic("Audio Engine", include_str!("../../docs/audio_engine.md")),