Rotary block

Available on which products

• Axe-Fx III, FM9, FM3: 2 blocks
• Axe-Fx II, FX8: 2 blocks
• AX8: 1 block

Channels or X/Y

• Axe-Fx III, FM9, FM3: 4 channels
• Axe-Fx II, AX8, FX8: X/Y

About rotating speakers (Leslie)

This Wikipedia article tells us:

The Leslie speaker is a combined amplifier and loudspeaker that projects the signal from an electric or electronic instrument and modifies the sound by rotating a baffle chamber ("drum") in front of the loudspeakers. A similar effect is provided by a rotating system of horns in front of the treble driver. It is most commonly associated with the Hammond organ, though it was later used for the electric guitar and other instruments. A typical Leslie speaker contains an amplifier, a treble horn and a bass speaker—though specific components depend upon the model. A musician controls the Leslie speaker by either an external switch or pedal that alternates between a slow and fast speed setting, known as "chorale" and "tremolo".

Also see Reverb.com's The Continuing Story of the Leslie Rotating Speaker Cabinet.

Rotary vs chorus

Chorus and rotary effects are not the same thing, but players often set a chorus to a fast rate to reproduce the sound of a rotary effect, and a slow rotary is a good, or better, substitute for a chorus.

Rotary block position on the grid

Many players put the Rotary block after the Amp block for stereo output.

It also sounds great before the Amp block, just like you would do with a digital or analog rotary pedal. Note that, unless you use two amp blocks, the Rotary will run in mono when placed before the Amp block.

Alternatively, run the Rotary in parallel to a Cab block.

Rotary block diagram

Mono or stereo

The Rotary block is stereo by default. You can change to mono output by setting Mic Spacing or Stereo Spread to 0%, or by summing its output to mono by placing it before the Amp block.

Spread values beyond 100% increase the apparent image beyond the stereo field.

Parameters

Rate

Part of the charm of the Rotary is switching between speeds. The effect will automatically ramp when switched.

For authentic behavior of the rotor, try 0.833 for the Chorale (slow speed) and 6.667 for the Tremolo (fast speed), based on values in the Harmony Central quote below:

• Horn:
  • Chorale: 50/60 = 0.833
  • Tremolo: 400/60 = 6.667
• Drum:
  • Chorale: 40/60 = 0.667
  • Tremolo: 340/60 = 5.667
  • Chorale Low Rate Multiplier: 0.667/0.833 = 0.8
  • Tremolo Low Rate Multiplier: 5.667/6.667 = 0.85

To switch between two speeds, use channels and use the same settings except for Rate, a control switch or MIDI:

• Set Min to 0.833 and Max to 6.667 in the Rate's modifier menu.
• Define a Control Switch that alternates between those same values.
• Program the MIDI controller to send 127 for fast and 0 for slow using the CC of the switch.

The repair manual recommends the ramp speed be between 5-8 seconds for the drum. 6.5 is a happy medium.

Braking the rotary means that the speed is slowed down until it stops. The Rotary block does not provide a built-in brake so set it to 0 for the Rate to accomplish the same thing. Leslie speaker cabinets had the option of a brake which can rapidly slow the drum and horn rotations, so adjust the Low Time Constant value to taste.

OTHER QUOTES

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Harmony Central:

[1] The sound changes in very interesting and fun ways when the Leslie's speed is switched. This is in part due to the different mass of the rotary horn and drum elements; when the speed is switched, the larger and heavier drum takes significantly more time to speed up or slow down than the horn does. The interaction of the sound from the two speakers -- the phase shifts and the sound reflections off the cabinetry, Doppler shift pitch changes and amplitude (volume / tremolo) fluctuations make for a very complex and interesting sound, especially when motor speeds are changed and as the drum and horn transition to the new setting. The effect on the upper horn is more FM, or frequency modulation in nature. As the horn spins towards the listener's position, the pitch of the sound rises slightly, and as it spins away from the listener, the pitch drops slightly. The sound of the Doppler shift changes, depending on the horn's speed. The horn rotates at about 50 RPM in Chorale mode, and about 400 RPM on the Tremolo setting. The drum has slightly slower speeds. It tends to rotate at about 40 RPM in Chorale, and 340 RPM in Tremolo mode. The drum can take five or six seconds to transition speeds, and the overall effect of the sound of the spin of the drum is more AM, or amplitude modulation in nature. Due to the lower frequency range, the effect is perceived as more or a up and down volume fluctuation as the drum turns towards and then away from the listener. Of course, there are some elements of AM and FM with both drivers, and the amount of this that you capture on your recording can be affected by how closely you place the microphone(s) to the cabinet, as well as the balance of horn to drum that you use in your mix.

For more information see:

• Hammond Organ's repair manual
• Harmony Central's Rotary Speaker Cabinet Miking page.

Mic Spacing, Mic Distance

FRACTAL AUDIO QUOTES

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[2] There is Mic Spacing which controls how far apart the virtual mics are and Mic Distance which controls how far the virtual mics are from the cabinet. The effect is subtle though.

Tips, tricks and troubleshooting

Factory presets

The Rotary block is present in many factory presets. Search the Factory presets page for rotary.

Tweaking the rotary

• If you want less or more throbbing, decrease Depth, or add some dry signal.
• To add more shimmer, increase High Level.
• Horn Length controls the modulation depth.
• Change the relative speeds of both rotors by adjusting Low Rate Multiplier.
• Adjust the Time Constant parameters to adjust the ramp up/down speeds.