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KDFX Reference
KDFX Algorithm Specifications
C2, C3) settings. The vibrato chorus has been carefully modelled after the electro-mechanical vibrato/
chorus in the B3.
An amplifier distortion algorithm follows the vibrato/chorus. The distortion algorithm will soft clip the
input signal. The amount of soft clipping depends on how high the distortion drive parameter is set. Soft
clipping means that there is a smooth transition from linear gain to saturated overdrive. Higher distortion
drive settings cause the transition to become progressively sharper or “harder”. The distortion never
produces hard or digital clipping, but it does approach it at high drive settings. When you increase the
distortion drive parameter you are increasing the gain of the algorithm until the signal reaches saturation.
You will have to compensate for increases in drive gain by reducing the output gain. These algorithm will
not digitally clip unless the output gain is over-driven.
The distorted signal is next passed to a cabinet emulation filter and a pair of crossover filters for band
splitting. The measurements of a real Leslie® speaker was used in the design of these filters. Default
parameter values reflect these measurements, but you may alter them if you like. The Lo HP parameter
controls a highpass filter which defines the lowest frequency to pass through the speaker. Likewise the Hi
LP parameter is a lowpass filter controlling the the highest frequency. The crossover filters for the lower
and upper drivers may be set independently. A small amount of overlap seems to work well. The gains of
the high and low band signals may also be separately controlled.
At this point KB3 FXBus has finished its processing and passes the high and low signals to the KB3 AuxFX
algorithm which contains the rotating speaker routine. The rotating speaker has separately controllable
tweeter and woofer drivers. The signal is split into high and low frequency bands and the two bands are
run through separate rotators. The upper and lower rotors each have a pair of virtual microphones which
can be positioned at varying positions (angles) around the rotors. An angle of 0° is loosely defined as the
front. You can also control the levels and left-right panning of each virtual microphone. The signal is then
passed through a final lowpass filter to simulate the band-limiting effect of the speaker cabinet.
Figure 10-50 Rotating speaker with virtual microphones
The rotating speakers for the high and low frequencies have their own controls. For both, the rotation rate,
the effective driver size and tremolo can be set. The rotation rate of course sets how fast the rotating
speaker is spinning. The effective driver size is the radius of the path followed by the speaker relative to its
center of rotation. This parameter is used to calculate the resulting Doppler shift of the moving speaker.
Doppler shift is the pitch shift that occurs when a sound source moves toward or away from you the
listener. In a rotating speaker, the Doppler shift will sound like vibrato. As well as Doppler shift, there will
be some acoustic shadowing as the speaker is alternately pointed away from you and toward you. The
shadowing is simulated with a tremolo over which you can control the tremolo depth and “width”. The
high frequency driver (rotating horn) will have a narrower acoustic beam width (dispersion) than the low
frequency driver, and the widths of both may be adjusted. Note that it can take up to one full speaker
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