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Getting The Best From Your Leslie Simulator

Tips & Techniques By Nick Magnus
Published November 1994

Using a Leslie no longer means dragging around a large wooden cabinet crammed with rotating speakers. More and more modern units and simulations are now available, and Nick Magnus dons his prog rock mantle to explain how to get the most from them.

Leslie simulations are now to be found within many multi‑effect units, such as the Alesis Quadraverb and Boss SE70, or built into the effect sections of instruments like the Korg Wavestation and the Roland JV1080. They tend to differ greatly in effectiveness and authenticity from device to device, but the most authentic incarnations seem to be found in dedicated units. The best of these (subjectively, of course) are Dynacord's analogue CLS222 and the digital DLS223, with excellent offerings to be found in the Korg G4 and Roland's SGX330. Among the best examples built into instruments is that of the Roland VK1000 organ, which sports a highly editable rotary effect, and the aforementioned Korg Wavestation also scores high marks for its version. These last two examples, however, are confined to use only on the host instrument, unless you are using a Wavestation A/D, which has analogue inputs enabling the treatment of sounds from the outside world.

Sound Tweaking

One of the principal characteristics of a Leslie cabinet is its tonal quality. Much more than just a pair of revolving speakers, the Leslie is a solid cabinet with gears, clutches and relays, louvred ports, and often a built‑in pre‑amplifier. It has a distinct tonal fingerprint which is unlike a regular speaker enclosure. Most importantly, the frequency responses of the upper 'horn' speaker and the lower 'drum' are completely separated by a crossover unit. They have no frequencies in common, which means that the rotary movements of each speaker are clearly distinguishable, with no 'mushing' in the middle audio spectrum. This implies that there is a substantial notch in the mid‑range response. Another consideration is high‑frequency content; the Leslie cabinet does not reproduce the same full range as a hi‑fi speaker, and there is some attenuation at the very high end — hardly surprising, as the rotating horn is shut in a box with only louvred slats as an outlet for the sound.

Referring back to our electronic simulations, the Dynacord CLS222 is supremely successful in the above areas. Listening to its horn and bass signals individually reveals no common frequencies, and whether by accident or design, the upper end is suitably attenuated. Stopping the rotor movement and listening to the sound with the effect switched in reveals a notched‑out quality similar to that produced by the real thing with its rotors stationary. The newer digital units could be said to suffer, if anything, from their 20Hz‑20KHz specification. The signal comes out as bright as it went in, and some tend to exhibit a wide band of frequencies common to both upper and lower speakers; neither of these properties are necessarily desirable for an authentic rotary simulation. Laudably, the Korg G4 is bestowed with a speaker simulator setting to correct the high end.

The sound of some units can therefore be improved by judicious use of a stereo graphic equaliser, preferably one with 1/3 octave increments. The mid‑range notch we need to create will be somewhere between 200Hz and 1KHz. To narrow down the search:

  • First isolate the bass signal, if the rotary unit allows this.
  • Whilst holding an organ chord somewhere around middle C, start lowering the sliders on the graphic, starting at the top end, until you detect that the upper harmonics are being attenuated.
  • Make a note of this frequency and reset the graphic to a flat response.
  • Now do the same listening to the horn signal only; this time the graphic's sliders will be lowered from the bottom upwards, until attenuation of the lower harmonics becomes obvious.
  • Note this frequency. You should find that the first figure is higher than the second, and it is the frequency range between those two noted values that we wish to eliminate.
  • Do this by lowering all the relevant graphic sliders. If this sounds too severe, try arranging the sliders in a truncated 'V' shape.
  • To top it all off, try a very gentle roll‑off starting around 6KHz, although the exact frequencies and the amount of reduction are ultimately down to experimentation and your own judgement.


The obvious use of the fast/slow speed control of a rotary speaker is to add excitement to a performance. Not that I would dream of lowering the tone of a serious article by using words like 'organ' and 'climax' in the same sentence, but dynamics are, essentially, what we're talking about. Rather than using the speed control indiscriminately, it makes good musical sense to follow the phrasing and structure of the music — you could compare the approach to going through the gears in a sports car. You can induce a sense of urgency as you progress through a verse by inserting a few brief accelerations at the end of each phrase, becoming slightly longer each time, until the end of the last verse line, where you crank the Leslie up to full tilt just as the chorus begins, holding it briefly and allowing the speed to slow down on a long sustained chord. The final chorus, when everything is probably playing at its loudest, may be an appropriate time to let the Leslie stay at its fastest speed.

On Or Off Mic?

Some Leslie simulators offer a choice of on‑ or off‑mic positions, notably the Dynacord DLS223, Boss SE70, Korg G4 and Roland SDX330. What exactly does this mean? When miking a real Leslie, the microphone position can drastically influence the sound, as you might expect. As well as the rotary effect, the cabinet also radiates a straight, unmodulated sound which is always present to some degree. This is because the speakers themselves do not rotate; it is only the horn and bass drum projecting the noise that are actually moving. Thus the closer the mic is to the rotating source, the more exaggerated are the volume and tonal sweeps. If the mic is moved away, it picks up more of the straight sound being reflected off the walls of the room, which is also mixed with delayed reflections from the rotors. This has the effect of smoothing out the overall intensity of the Leslie sound. You would use the off‑mic position to simulate a 'clubby' sort of sound, while the on‑mic position is often favoured for a heavy, demonstrative rock approach.

For stereo units which have no on/off mic facility, such as the CLS222, an effective way of exaggerating the rotary effect is as follows:

  • First, try muting one side of the stereo picture. You will notice that the resulting modulations are now very intense. This is because the panning of the sound to the muted channel causes it to disappear briefly.
  • Now unmute the channel with its fader set at zero and gradually reintroduce that signal into the mix until the modulations have smoothed just a little. The stereo picture will be lopsided (assuming that the desk pans were hard left and right), so you'll probably want to bring it a bit closer in. You will naturally be sacrificing a little stereo width in doing this, but it will help to blend the overall sound.

Leslie Tips

  • If your unit has a treble/bass balance control, use it to help the sound sit with the other instruments in the track. Although a very full‑sounding organ or guitar may be great on its own, it can bulldoze an ungraceful path through the mix. Setting the treble horn to be quite dominant means that the instrument takes up less sonic space, but still retains a sense of power, and the rotary movements are pleasingly prominent.
  • Percussion sounds, particularly high‑frequency ones like hi‑hats, cabasa and shakers, can also benefit from this type of effect. Try these with the bass balance turned right down so that only the panning movements of the treble speaker have any influence. Or, with the treble/bass balance set at 50/50, combine them with lower frequency percussives, such as surdo, Indian drums or similar. These opposing types of sound will pan independently in accordance with the speaker movements.
  • The rotor stop setting, too, can be used to dramatic effect. Try slowly fading in an organ chord with the rotors stationary, then at the crucial moment, kick the speed up to fast, and as soon as full speed is reached, slam on the brakes to the slow position, settling down into a glorious swirl.