Rotary Speaker emulation pedal
By Phil O'Keefe
One of the most difficult effects to really nail is the sound of a rotating speaker cabinet. First invented back in the 1940s by Don Leslie, the interaction of a rotating high frequency horn (above 800Hz) and spinning low frequency drum rotor results in a quite complex and distinctive sound that is difficult to fully emulate; with elements of tremolo (amplitude modulation), Doppler-effect pitch shifting, phase shifting and a lot of echoes and reflections off the interior of the cabinet and surrounding room surfaces all happening simultaneously.
Strymon has been having great success lately with their SHARC based DSP pedals such as the El Capistan delay, and they have now turned their attention to dedicating that considerable processing power to doing one thing -- capturing the sound of the rotating speaker in a compact pedal. That pedal is named the Lex. (Figure 1)
Figure 1: Strymon Lex rotary pedal
CONNECT UP TOP
The Lex uses the same basic case as several of Strymon's other pedals - a rugged brushed aluminum enclosure that looks like it will hold up to heavy use. The brown color subtly recalls the furniture grade wood cabinets of the classic rotating speakers. Input and output jacks are all top-mounted, as is the standard 9V center negative "Boss style" power jack. (Figure 2)
The Lex is a mono in, stereo out pedal, but it can be used as a mono in / mono out unit too. A "bi-amp" mode allows you to route the bass rotor (and frequencies below 800Hz) to the left output, while the high frequency horn is routed to the right output. I tried this using a SWR bass amp for the lows and a Vox AC15 guitar amp for the highs. It yielded some interesting sounds and allowed me to optimize the amp and speaker for each output's frequency range -- just as with a real Leslie cabinet, but overall, I preferred the stereo "swirl" of the standard stereo output configuration running into two guitar amps. It would be fantastic if the pedal offered a separate mono out for the bass rotor and stereo high frequency outputs, but that would have required a larger enclosure to fit the extra jack, and most users will probably be using the pedal as a mono in / mono out unit anyway. Interestingly, when the pedal is bypassed in bi-amp mode, the full-range true-bypass signal is routed only to the high frequency (right) output and the left output is muted. Still, it's nice that Strymon has given the user a choice in terms of how the outputs are configured.
Figure 2: All the connections on the Lex are located at the top of the pedal.
The basic control layout of the Lex is fairly straightforward on the surface. There are four knobs:
These give the user the basic settings that they need to dial in some pretty convincing Leslie tones. Special mention should be given to the preamp drive -- it's excellent, and it really captures the classic 40W Leslie amp sound. Don't be shy! Add in a healthy amount -- it adds a lot to the realism of the Lex's overall emulation. The Fast Rotor control affects both the horn and the drum speeds simultaneously. Unfortunately, there is no way to fine-tune their speeds individually. The Mic Distance control makes a big difference in the overall "sound" of the Lex. Turning it counter-clockwise places the virtual "mikes" right next to the horn and drum, and really emphasizes the Doppler shift and amplitude modulation (tremolo) elements of the sound, while turning the knob fully clockwise gives the Lex less volume fluctuation and the smoother, more ambient sounding wash of sound that is typically heard when placing the microphones further from the speaker cabinet.
As with most of Strymon's pedals, each knob has a primary function, as well as a secondary one. You access the secondary functions by pressing and holding down both the footswitches, and adjusting the knob while keeping them held down. This can be a bit tricky, but you'll quickly get the hang of it. As with the El Capistan, I wish the Lex had the names of the alternative control functions silkscreened directly on to the front panel, but the Lex is a somewhat simpler pedal in terms of the controls, and you'll learn the alternative functions relatively quickly. It helps that Strymon put some thought into the assignments, and they generally make sense. For example, the Fast Rotor Speed knob's alternative function is Slow Rotor Speed. The Preamp Drive becomes a output Level trim (+/-6dB) control. This can be very handy for dialing in unity gain from the Lex, or for setting it so you get a slight boost when the pedal is engaged.
Holding the Fast / Slow footswitch down engages a "brake" function, where the horn and drum speeds slow down to a complete halt. Strymon thoughtfully made sure that when they come to a halt, they are 'facing forward" instead of coming to a halt while facing in a random direction. When the switch is released, the Lex ramps back up to whatever speed you had it at before the brake was engaged.
A fourth quarter inch jack on the Lex is designed for use with an expression pedal. The obvious use for this would be to allow you to change the rotary speed (and conveniently, the fully heel down pedal position also kicks in braking in this mode) but literally any control on the pedal can be assigned to expression pedal control. I particularly liked using the expression pedal to control the Preamp Drive knob. This allowed me to add extra grit and growl to individual notes and phrases as I was playing, while still allowing me to change rotor speeds via the Lex's fast / slow footswitch. I also liked assigning the Horn Level control to the expression pedal. This allows you to vary the balance of the treble horn and bass rotary drum on the fly; letting you go from dark and brooding drum dominated tones to full-range sounds and anywhere in between. The expression jack can also be used to connect Strymon's optional "Favorite" footswitch. This $49 add-on can be used as a remote fast / slow switch, or to save a preset of your favorite settings for later recall. This works exactly as advertised, and the very useful Favorite footswitch is recommended for all -- except maybe those die-hard expression pedal fans...
THE BIG QUESTION
How does it sound? For that, put the Lex to the most brutal tests I could imagine -- I pulled out the Leslie 142 and Speakeasy tube preamp we have here in the studio, and plugged the Lex into a pair of guitar amps (AC15 and a Princeton) and did some side by side listening comparisons. I used the controls on the Lex to try to match the characteristics of this particular Leslie -- the ramp speed, the fast and slow rotor speeds, the preamp sound and the balance of horn and drum -- as closely as possible. Then I did the same thing with some recent organ recordings that I had used the Leslie on. I took the raw MIDI organ virtual instrument's output and fed that into the Lex and used it to process the track. Again, the goal was to try to duplicate the sound of the "real thing", or at least see just how close I could get.
I was able to get pretty darned close. Even when connected to a single mono amplifier, the Doppler and phase shift sounds very natural. Again, the preamp drive is pretty remarkable in terms of the accuracy of its tone and vibe. Ramp up and down are both very convincing, with the typical inertia based properties of the relatively light weight horn and the far heavier and bulkier drum being accurately represented. As you'd hope, their corresponding differences in response times when changing speeds is dead-on with the Lex; the drum takes far longer to speed up or slow down than the horn does -- just like on the real thing. And that leads to lots of cool phase and pitch shifts and changes to the sound as the speeds are changing. If you're the type of player who likes to "work the switch" a lot rather than leave it at one speed all the time, you're going to really like the Lex. It does those all-important transitions between speeds beautifully.
The main thing I felt the Lex was "missing" was the stuff that a lot of people complain about when they attempt to record a "real" Leslie; the mechanical and wind noise is absent. You don't get a click or clunk from the solenoid speed switching of a Leslie with the Lex. Okay, that part I really don't miss, but believe it or not, I do kind of miss some of the wind and mechanical noise. Click the switch to go from slow to fast on a real Leslie, and the whir of the spinning drum and horn ramps up, gets louder and changes pitch, and various mechanical clunks and noises also tend to increase. It's similar to changing speeds on a box or oscillating fan. Yes, I spend a lot of time trying to minimize that noise when I record a "real" rotating speaker, but you can never eliminate it entirely, and I think the Lex would actually sound even more convincing and authentic if it had the ability to add some of that back in with one of its controls. As it is now, it sounds very convincing -- especially when recorded. But if I had to pick the number one thing that I think people would subconsciously cue in on when trying to guess whether they're hearing a Lex or a Leslie, it would be those noises. Despite the fact that the rest of the simulation is exceptionally good, once you realize the noise isn't there, you can pick the Lex out every time, even in double-blind listening tests.
The comparisons I made were pretty harsh, but the Lex held up remarkably well. While sitting in the room with all the amps and speakers just a few feet away from me, I didn't quite experience the same full, three-dimensional, 360 degree sweep and swirl to the sound from the Lex and two stationary guitar amps as I did from the spinning Leslie, but I didn't really expect to. Still, the overall sound is really quite similar. On recordings, the illusion was even more convincing, and with a little studio slight of hand, I suspect I could fool most of the people, most of the time. In a live setting, I believe that if you had a Leslie cabinet shell sitting on stage just as a prop, and used the Lex instead, you'd also fool a lot of people -- especially if you ran it in a bi-amped or stereo configuration. I do wish there was a dedicated out for the "drum" - the bi-amp and stereo going together would absolutely slay in terms of realism. But again, most folks will probably run it in mono. It sounds good in mono, but you really should try it bi-amped. Or in stereo. Things get much more interesting, realistic and lusher sounding, and you gain some actual physical movement as the sound swirls between the two amps and speakers.
I've heard a lot of simulators over the years that have tried to nail the sound of a rotating speaker, and the Lex is right up there at the top of that list. If you can't afford or don't want to have to cart around the considerable bulk of a real rotating speaker cab, but still crave the swirly goodness, the Lex is definitely a pedal you should check out. Considering the complexity and variables of the device it is trying to emulate, the simulation is very impressive.