Speed
How fast the rotary speaker illusion spins.
- Turn up Faster Doppler swirl.
- Turn down Slow, lazy rotor.
Pedals / Rotary speaker
Lester K (Leslie rotary)
Rotary speaker · play-tested
seth — fish
seth@ninevolt:~$
Knobs
In the TUI each knob runs from low (left / 0%) to high (right / 100%). Start near noon, then nudge while you play.
Depth
How strong the rotary motion is.
- Turn up More dramatic swirling.
- Turn down Gentler motion.
Drive
Extra grit in the rotary path.
- Turn up Dirtier, more pushed rotary tone.
- Turn down Cleaner swirl.
Brake
Slows / brakes the rotor feel (higher = more braked / stopped character).
- Turn up More braked, less spin.
- Turn down Freer spinning motion.
Inspired by
Electro-Harmonix Lester K — stereo Leslie rotary emulator for the B9/POG organ stack. Hardware: Slow / Fast speed knobs, Balance (horn vs drum), Drive (tube growl), Brake footswitch with ramp. Lester K manual (PDF) — slow center horn 0.8 Hz / drum 0.7 Hz; fast center horn 6.2 Hz / drum 5.9 Hz; brake decelerates both rotors over several seconds.
Physical Leslie behavior (PASP — Leslie, CCRMA Doppler paper): horn = treble path with directional AM + small Doppler pitch shift (~2–20 cents); woofer port = bass AM throb (not pitch); cabinet reflections add chorus; stereo pan is essential on hardware. GeoFex LERA models brake ramp only (RC + opto into an effect’s LFO speed pot) — not the Leslie tone itself.
Signal path
| Step | What it does |
|---|---|
| Tube Drive | Drive — asymmetric soft clip before rotary sim (Lester K preamp growl). |
| Crossover ~850 Hz | Splits woofer-port bass from treble horn — Leslie cabinet crossover. |
| Drum AM throb | Bass AM at drum rate (ramps slow↔fast with Brake). Main woofer effect per PASP. |
| Drum / horn pseudo-pan | Opposing ±28% band gains — mono stand-in for stereo spin. |
| Horn AM | Treble AM at horn rate — directional horn radiation. |
| Dual modulated allpass | Two quadrature phase paths on horn — stronger swirl without chorus ms sweeps. |
| Physics-scaled horn Doppler | Light blend (~35% max) of sub-ms delay sized to ~2–20 cents. |
| Dry/wet Depth | Depth → 5–95% effect mix + AM / phase depth. |
| Brake ramp ~3 s | Horn and drum rates smooth toward slow/fast targets (LERA-inspired). |
How we modeled it
Leslie ≠ chorus. Prior versions used multi-ms delay sweeps on the full signal — that reads as pitch warble, not cabinet spin. Authentic Leslie loudness comes from crossover dual-rotor AM (bass throb + treble flutter at independent rates) plus tiny horn Doppler (~2–20 cents from horn geometry). Brake ramps both rotors per the Lester K manual. Depth sets AM depth and wet mix.
Simplifications
- Mono — no true L/R horn pan (pseudo-pan + dual allpass approximate spin) - Depth replaces separate Balance + mix knobs - One-pole crossover vs Leslie 800 Hz–1 kHz network