PreSonus Blog

Friday Tip: Rotating Speaker Emulator FX Chain

A rotating speaker is an extremely complex signal processor (as most mechanical signal processors are—like plate reverbs). It combines phase shifts, Doppler shifts, positional changes, timbral variations, and more. And of course, Studio One includes the Rotor processor, which does a fine job of capturing the classic rotating speaker sound.

However, I’ve always felt that rotating speakers have a lot more potential as an effect than just emulating physical versions—hence this FX chain. By “deconstructing” the elements that make up the rotating speaker sound, you can customize it not only to tweak the rotating speaker effect to your liking, but to create useful variations that don’t necessarily relate to “the real thing.” What if you want a speed that’s between slow and fast? Or a subtler effect that works well with guitar? Or simulate the way that the horn spins faster when changing speeds because it has less inertia than the woofer? This FX chain provides a useful, more subtle variation on Rotor’s rotating speaker sound—check out the audio example—but the best way to take advantage of this week’s tip is to download the multipreset, roll up your sleeves, and start playing around.

Rotating speaker basics. There are two rotating speakers—one high-frequency driver, and one low-frequency drum. A crossover splits the signal to these two paths, so we’ll start the emulation by setting the Splitter to Frequency Split mode around 800 Hz. Here’s the routing.

The high-frequency and low-frequency paths each go into a Flanger to provide Doppler and phase shifts, and an X-Trem for subtle panning to provide the positional cues. Let’s look at the individual module settings.


The Analog Delay adds a 23 ms reflection for a bit of a room sound vibe, with some modulation to add a Doppler shift accent. Finally, an Open Air reverb (using the 480 Hall from Medium Halls) creates a space for the rotating speaker.

Knob Control. This was the hardest part of the emulation, because changing speed has to alter (of course) Flanger speed, but also the Flanger’s LFO Width because you want less width at faster LFO speeds. The X-Trem speed and Analog Delay LFO speed also need to follow the range from slow to fast.

However, the curves for the control changes are quite challenging because the controls don’t all cover the same range. Fortunately you can “bend” curves in FX Chains, but you can’t have more than one node. As a result, I optimized the knob settings for the lowest and highest speeds—besides, a real rotating speaker switches to either speed, and “glides” between the two settings as it changes from one to the other. An additional subtlety is that the high-frequency “speaker” needs to rotate just a little faster than the low-frequency one. Also, they shouldn’t track each other exactly when going from the slowest to the fastest speed because with a physical rotating speaker, the low-frequency drum has more inertia.

All these curves do complicate editing any automation, because you need to write-enable each parameter when you turn the knob. So if you need to change some automation moves you made, I recommend not trying to edit each curve—just try another performance with the knob.

Oh, and don’t forget to try this on instruments other than organ!



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