WMD Phase Displacement Oscillator and Friends

WMD-PDO

Pictured are three modules from WMD that constitute a system for phase modulation.

Triple Bipolar VCA

On the left is the Triple Bipolar VCA.  This is a high-quality DC-coupled VCA that can be used in any capacity where a VCA is needed in a modular system.  I like this VCA enough to recommend it for stand-alone use.  The bipolar emphasis means that it excels at inverting.  Each VCA has a Bias pot, which is the initial gain.  But it’s reversible!  This is a VC-attenuverter.  The CV input also inverts.  Moreover, there are both normal and inverting signal inputs, but they work in a rather unexpected manner.  When the summed CV is positive, the non-inverting signal goes to the output, and when the CV is negative, the inverted signal is passed.  If two different signals are patched, you get a zero-off fading function.  WMD did a good job of having a null point in the center of the CV, where no signals pass.  The Triple Bipolar VCA has jumper cables to the PDO, so it takes the first three PDO phase outputs, as normalled to its three inputs, and its three ouputs are normalled to the PDO phase CV inputs for phases two through four.  Watch out, the three CV inputs to the VCA are also normalled together.  And note the mix output of all three VCAs, making this a voltage controlled mixer to boot.

Quad Anti-Aliasing Filter

On the right side is the Quad Anti-Aliasing Filter (QAAF).   The QAAF is specially designed to work with the PDO.

The WMD 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. We opted to make this a separate module because it is useful by itself as well as coupled with the PDO.

There are four independent filters inside the QAAF. Each -24dB/octave Butterworth filter runs at exactly the same frequency. The Butterworth filter has a small amount of resonance and a great sound. Each input jack is normaled from the expansion header that connects to the PDO, but any signal can be filtered by plugging in.

The QAAF is the only relatively traditional filter in my Wave Mangling System.  It has a nice vactrol response.

Phase Displacement Oscillator

The PDO is a VCO especially designed for doing phase modulation.

The PDO exists to utilize the phenomenon of Phase Modulation (PM). This allows for the relative phase difference of its outputs to be set or modulated, producing very interesting sounds. The result is similar to Frequency Modulation (FM) but affects the output to a greater degree without affecting the stability of the initial frequency. This is where the “displacement” comes in.

When you use frequency stable phase displacement, you create phase distortion which sounds like wave folding and is very useful for dynamic textures and powerful sounds.

The PDO excels at self-modulation.  Here’s a demo of it self-modulating, where I manually adjusted the depths of modulation.

 

There’s no way I can begin to explain all the ways this system can be utilized.  A great document has been published that you can refer to.

PDO-Triple-Bipolar-VCA-Manual

Finally, here is a little demo of a more complex patch, using these modules.

 

 

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