phaser~

Adds a phase-shifted sound to the original sound, producing a swirling modulation that creates spaciousness and depth. Three different methods are selectable and one can control the frequency and range of the modulation, also providing different control wave forms.

version

v1.0: built 5/04/2007 with Pd v0.40-2 [pd] [pdf]

interface

Input1: incoming mono audio signal
Input2: this inlet takes values between 0 and 127 that specify the frequency of the control waves. It stands for the RATE parameter.
Input3: this inlet takes values between 0 and 127 that specify the range of the control waves. It stands for the DEPTH parameter.

Output1: The phase shifted mono signal that is output.

Controls:
Different control curves: For a sine wave, sawtooth, triangle or square wave, currently the MIDI control messages are assigned this way: respectively 52, 53, 54, 55.
Different phaser implementations: Also assigned with MIDI control change messages: 4 allpass stages is 56, 3 times 4 stages is 57 and 6 stages is 58. The default is four allpass stages.

implementation

The basic building block of the phaser is a pd allpass~ block. As seen in the figure it is a real one-zero (non-recursive) 'reverse' filter followed by a real one-pole (recursive) filter, both with the same coëfficiënts. For visual reasons, the coëfficiënts are passed to an outlet. This combination thus presents one stage of allpass filtering. This leaves the gain of all frequencies unchanged, but it alters the phase response.
The coëfficiënts of these allpass filters are altered in time. The waves block outputs a specific control curve with a chosen frequency (RATE). This curve (that lies between 0 and 1) is then scaled with the DEPTH parameter and it is also offset to lie under one. The DEPTH parameter is divided by 131 because the maximum value of the curve is 0.97 and when a range is chosen it can maximally extend to zero. The maximum value that can be passed is 127, so the 131 divides the interval maximally.
With the select and ctlin block one can choose between three setups. The A-form (A has no special meaning) uses four stages and outputs the signal coming from the last stage. The B-form, that sounds more boosted, uses three times four stages and sums every block of four stages. The C-form is another widely spread form that uses 6 allpass stages.