11.3

HALF-RACK EFFECTS696
PH-90 Phaser
The PH-90 Phaser is a classic phaser effect with some special features for fine-tuning the sound. It can create the
classic sweeping phaser sounds suitable for pads or guitars, but also more extreme effects if you like. The phaser is
best used as an insert effect.
Theory
A phaser works by shifting portions of the audio signal out of phase, and then adding the processed signal back to
the original one. This way, narrow bands of the frequency range (“notches”) are filtered out. When these frequencies
are adjusted, a sweeping phaser sound is created.
The PH-90 is a four-stage phaser, which means that there are four “notches” in the frequency response curve (this
is a little like using four notch filters with different filter frequencies - see “Notch” in the Subtractor chapter for an ex-
planation of notch filters).
When the phaser frequency is adjusted (manually or by the built-in LFO), these notches will move in parallel in the
frequency spectrum. Furthermore, you can adjust the distance between the notches (Split) and their Width. Adding
feedback raises the filter gain just below each notch in the frequency range, creating a more pronounced effect.
Parameters
CV Inputs
The following CV inputs are available on the back panel of the device:
•Freq CV.
Adjusts the frequency parameter. Use this e.g. for creating envelope controlled phasing (preferably with LFO Freq.
Mod turned off in the device).
• Rate CV.
Lets you control the speed of the modulating LFO from another device.
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Parameter
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Description
Frequency Sets the frequency of the first notch. Adjusting this will move the other notches correspondingly. This is the parameter
modulated by the LFO to create phaser sweeps.
Split This adjusts the distance between the notches in the frequency range, thereby changing the character of the effect.
Width Determines the width of the notches. Raising the Width deepens the effect and simultaneously makes the sound
more hollow and thin. This will also have an effect on character of the feedback “tone”.
LFO Rate This is the speed of the LFO modulating the frequency parameter. The higher the value, the faster the phaser sweeps.
LFO Sync This button lets you activate/deactivate LFO sync. When it is activated, the frequency of the LFO is synchronized to
the song tempo, in one of 16 possible time divisions. The LFO Rate knob is then used for setting the desired time di-
vision. Turn the knob and observe the tooltip that appears for an indication of the time division.
LFO Freq. Mod This determines the depth of the LFO modulation, i.e. by how much the frequency parameter should be modulated.
If you turn this to zero, the effect will be a static, formant-like sound (most effective if you add a little feedback).
Feedback This is similar to the resonance control on a filter. Raising the feedback gives a more pronounced “tone” in the effect.
For “singing” phaser sounds, try raising this to the maximum.