The WMDevices Quad Anti-Aliasing Filter (QAAF) was conceptualized as the first expansion for the Phase Displacement Oscillator.
It is designed to eliminate aliasing and stair-step distortion from the Digital to Analog converters. WMD opted to make this a separate module because it is useful by itself as well as coupled with the PDO.
Controls and I/O
- CV Input - This input is roughly calibrated to 1 v/octave. It drives a vactrol that will cause the QAAF to open quickly and close slowly.
- Freq Knob - This knob controls the cutoff directly or acts as a bias/level shift control for the CV input.
- CLK - This jack serves as a clock input or output, directly controlling the filter's frequencies at a ratio of 100:1. A jumper on the back (lower jumper) selects it's mode. Jump for clock output, leave open for clock input.
- Inputs 1-4 - Audio Inputs, these are normaled from the expansion header going to the PDO. This normal is broken by plugging into these jacks.
- Outputs 1-4 - These jacks are for each channel's outut.
- Mix - This output is a sum of each channel's filtered input.
- Frequency Limit Jumper - This rear jumper (upper set of pins) will limit the low frequency cutoff to about 300 Hz. This will stop the QAAF from producing aliasing noise itself as it's clock frequency will be limited to 30 kHz. Jump for limiting, leave open to disable.