Mar 26, 2018

The rotary speaker effect has a come a long way since it was unmoored from its mechanical origins [go here for a quick history of this effect and its functionality].

Initially created for the Hammond organ in the late 1930s, the shimmering modulation known as the Leslie effect became the tone du jour for guitarists in the late 1960s. George Harrison and Eric Clapton were both adoptees and used Leslie cabinets in the studio, while Pink Floyd’s David Gilmour opted for a Leslie 900, Yamaha’s RA-200 and even Maestro’s short-lived Rover. And let’s not forget Beatles engineer Geoff Emerick, who famously employed the effect on John Lennon’s voice to make him sound like he was singing from the top of a mountain on the 1966 Revolver track “Tomorrow Never Knows.”

Effect pedals that electronically mimic the pitch and volume modulations produced by physically rotating speakers date back to the 1960s. The 1968 Shin-ei/Univox Uni-Vibe was the first unit trying to create a similar effect without mechanical parts and was favored by Jimi Hendrix and Robin Trower. Morley’s 1971 RWV Rotating Wah Volume oil-can pedal and Dunlop’s Rotovibe Chorus/Vibrato pedal were later variations that became favorites of many guitarists.

But until recently, if you wanted to bathe your guitar tone in the exhilarating rush of rotary tone, you had to haul the real thing—most likely the “portable” Leslie 16 cabinet, rebranded as the Fender Vibratone after CBS Musical Instruments, Fender’s parent, purchased Leslie in the 1960s. (The Leslie 16 was identical to the model 18, except that it had a facility for connecting the cabinet to a standard combo amp’s auxiliary speaker output.)

Today, however, convincing rotary speaker emulations are offered in stompbox format by a number of manufacturers. Let’s take a look at what options are available on the current market.

The real question here is: do you want a digital Leslie emulation or an analog effect that mimics it? The difference is down to a few of things:

First, a true Leslie emulation will be stereo and possess a depth of realism you’re unlikely to find in an analog pedal.

Second, many Leslie emulations include EQ circuits that simulate the speakers and cabinet tones of popular Leslie models, like the 122, the 147 and the 16/18.

Third, Leslie emulators feature two speeds—Chorale (slow) and Tremolo (fast)—and will ramp up and down between these speeds when you switch between them, rather than jump from one speed to the other. Full-featured pedals will let you set both the Chorale and Tremolo rates, the speed at which the pedal ramp up or down as you change between them, and many other parameters that are important to creating a convincing Leslie emulation.

We’ve divided the current market offering into five categories. Vintage Modulators includes pedals that deliver an inspired take on the classic Uni-Vibe. No-Frills features stompboxes that offer convincing Leslie tones at the press of a button, with no muss and no fuss. Something Extra is set aside for a pair of noteworthy Robert Keeley pedals that deliver rotary emulations along with additional effects. Leslie Emulators go further than the previous entries, giving you control over slow and fast speeds, a natural-sounding ramp up and down as you change between them, stereo outputs and other niceties. Finally, there are the Deluxe Emulators that go for ultimate realism and mimic the characteristics of true Leslies with features like tube overdrive, virtual microphones with distance control and so on.

So much for the explanations. Let’s get this round-up in motion.

Fifty years since its debut, the Uni-Vibe remains a quintessential modulation effect – and one of the most popular pedals, see our comprehensive list of Uni-Vibe stompboxes. Recreations of the original effect make up the bulk of our vintage category and include the Fulltone Mini Dejávibe, the Voodoo Lab Micro Vibe, the BBE Soul Vibe and the Dunlop Rotovibe, which is unique among this group for featuring a treadle that lets you change speed in real time.

Click on the thumbnails to see a video of each pedal.

If you want convincing rotary tones in an easy-to-use pedal, these should do the trick. With Chorus and Vibrato settings, the Mooer Soul Shiver seems like a Uni-Vibe clone until you kick it into Rotary mode, where it delivers shimmering Leslie-like tones. The Tomsline Engineering Roto Engine is a similar beast, with modes for Chorus, Phaser and Vibe. There aren’t many videos of the pedal in action, but the two we found convinced us that it’s more than a Uni-Vibe clone, delivering suitably watery rotary tones that might make your audience think you’re using a real Leslie cabinet.

For a little more control, there are the Billionaire by Danelectro Big Spender Spinning Speaker and Hotone Audio Roto, a pair of Leslie emulators that feature a facility to change between Chorale and Tremolo speeds. The Billionaire pedal even has a ramp control.

Finally, there’s the Neo Mini Vent II. Neo turned a lot of heads a few years back with its Ventilator, a desktop Leslie emulator designed for organists. Since then the company has placed that circuitry in the guitarist-friendly Ventilator II (see below under Deluxe Emulators) and the Mini Vent II, a simple little box that gives you just what you need for convincing Leslie tones.

We were a little hard-pressed to figure out where to put these two entries from Robert Keeley. Both are rotary-speaker simulators but they include additional features that make them neither Uni-Vibe clones nor No-Frills pedals. Rather than let them get lost in the shuffle, we decided to reward their uniqueness by giving them their own category.

The Monterey Rotary Fuzz Vibe produces rotary-speaker tones but also has fuzz and octave up/down circuitry, so it’s considerably more than a rotary-style effect. The Dyno My Roto is both a Leslie simulator and a chorus and flange pedal, and like the Monterey it gives you more bang for your buck. It even has a Proximity Control to impart mic-and-cabinet emulation. Its mono output and lack of ramp control prevent it from being a full-on Leslie emulator, but as the video demonstrates, it sounds fantastic.

Here’s where the game gets serious. The pedals in this category deliver convincing Leslie emulations along with a feature-rich set of controls, including horn/bass rotor balance or microphone emulation, and stereo outputs. The entries include the Strymon Lex, the Tech 21 Roto Choir, the Boss RT-20, the Electro-Harmonix Lester G, the Pigtronix Rototron and the Digitech Ventura Vibe.

If you’re all about the Leslie effect, you can’t do better than these three emulators. As mentioned above, Neo Instruments blew everyone away with its Ventilator, a desktop-style pedal that emulates the Leslie 122, one of the most famous cabinets in the company’s historic lineup. While the Ventilator’s feature set is no richer than what’s offered on some pedals in the Leslie Emulator category, the quality of its emulation is truly exceptional, with a depth of realism that few can match. For guitarists, Neo created the Ventilator II, which offers the same features in a smaller format, along with expression pedal control.

Experimental Noize offer the SpinCycle, an emulation of the 122 cabinet that offers control over standard parameters like speed, acceleration, balance and mic distance, plus innovative features like separate speed controls for the treble and bass rotors, adjustable braking rates, tube emulation and more.

Finally, there’s the Leslie G, Leslie’s own entry in the rotary-speaker emulation market for guitarists. The pedal is a smaller version of its Digital Leslie Pedal. That unit features emulations of the 122, 147 and 18 model cabinets, as well as the Hammond PR-40 tone cabinet, a stationary-speaker cabinet that was standard issue with Hammond organs in the 1950s and 1960s. (The addition isn’t so surprising when you consider that Leslie is now marketed under Hammond.) The Leslie G loses the PR-40 emulation, which is no great loss, and instead lets you store a preset or your own creation.

The rotary speaker was created in the late 1930s by Donald Leslie, a repairman at Barker Brothers Department Store in Los Angeles, which sold and serviced Hammond organs. Leslie was unhappy with the organ’s static sound and deduced that pipe organs sound so good because their pipes are stacked side by side, usually in a staggered arrangement and sometimes even split into separate divisions placed several feet apart. He figured the best way to emulate this was to scatter the sound so it wasn’t emanating from one place.

Leslie set out to create a “moving” speaker that would rotate on its axis and throw the sound as it spun. His original design used a spinning treble horn, but he later improved on it by employing a crossover circuit to split the high frequencies, which went to the horn, from the low frequencies, which were fed to a large speaker that faced downward into a rotating drum-shaped baffle. Though his early cabinet had one speed—Tremolo (fast)—he later created a slower speed, called Chorale, so that the sound was always in motion.

While Leslie has gone down in history for his creation, it appears that the Allen Organ Company was marketing a cabinet based on the idea at the same time or possibly slightly before him. The Gyrophonic Projector, as it was called, was designed to work only with Allen organs. According to one description, it featured three 12-inch loudspeakers and three 3-inch tweeters mounted on a vertically rotating wood disc—obviously not as tidy a design as Leslie’s and perhaps the reason why it never caught on. You can see a modified example in the video below, with a guitar used in the demonstration.

Rotary speakers exploit the Doppler effect, which causes the pitch and volume of a fast-approaching object, such as a police siren, to rise as it nears the listener and lowers once it passes and recedes. As the Leslie’s rotary speakers spin, they cause the pitch of the sound produced through them to waver slightly but perceptibly as the horn and speaker baffle spin toward and away from the listener. At the same time, the volume fluctuates gently. Together, this creates a fluid shift in pitch and volume, effects that we know as vibrato (pitch modulation) and tremolo (amplitude modulation).

But recreating this effect electronically isn’t as easy as combining vibrato and tremolo. The physical dynamics of a true rotary speaker are complex and difficult to emulate. Digital signal processing (DSP) has made it possible to create convincing emulations of the effect, but that’s not to say earlier analog attempts at mimicking the Leslie were failures. Far from it. The Uni-Vibe did a good job of copying the rotary speaker’s watery tremulousness, and it remains a desirable effect in and of itself even as convincing rotary emulations have come to market.

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