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FX Algs #156-160: Phasers

              

Allocation Units: 1 (each)

A simple phaser is an algorithm which produces a vague swishing or phasey effect. When the phaser signal is 
combined with the dry input signal or the phaser is fed back on itself, peaks and/or notches can be produced in the 
filter response making the effect much more pronounced. Most of the phaser algorithms presented here have built 
in low frequency oscillators (LFOs) to generate the motion of the phasers. In the case of Manual Phaser, the phaser 
motion is left to the user.

A phaser uses a special filter called an all-pass filter to modify the phase response of a signalÕs spectrum without 
changing the amplitude of the spectrum. As the name suggests, an all-pass filter by itself does not change the 
amplitude of the frequency response of a signal passing through itÑit does not cut or boost any frequencies. It does 
cause some frequencies to be delayed a little in time, and this small time shift is also known as a phase change. The 
frequency where the phase change has its greatest effect is a parameter that you can control. By modulating the 
frequency of the phaser, you get the swishy phaser sound. With a modulation rate of around 6 Hz, an effect similar 
to vibrato may be obtained, but only in a limited range of filter frequencies.

By adding the phaser output to the dry input using, for example, a Wet/Dry parameter, you can produce peaks and 
notches in the frequency response. At frequencies where the phaser is Òin phaseÓ with the dry signal, the signal level 
doubles (or there is a 6 dB level increase approximately). At frequencies where the phaser and dry signals are Òout 
of phaseÓ, the two signals cancel each other out and there is a notch in the frequency response. You can get a 
complete notch when Wet/Dry is set to 50%. If subtraction is used instead of addition by setting Wet/Dry to -50%, 
then the notches become peaks and the peaks become notches.

AP

Input

Output

Dry

Wet

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