4 identical channels to move a sound source further into the distance or closer to the listener. In circuit terms, each channel is simply a 6dB/oct filter with LP and HP outputs. LP and HP outputs can be summed for an Allpass output that could be used for variable phase shifting (max 90 degrees per channel). Distance changes the amount that the control signal effects the amplitude or cutoff frequency, Origin controls bias or offset.
Human perception seems to always be logarithmic. This is shown repeatedly in psychoacoustic studies into loudness perception, where, whilst there are frequency dependent behaviours that come from the physical apparatus of the ear, with a 1kHz pure sine, the relationship between SPL and perceived loudness is purely logarithmic. For this reason the control curve of each channel of the VCA is exponential (so the 2 different responses cancel). On a conceptual basis, the logarithmic nature of perception may be due to the exponential nature of stimuli in the world, where the sensory data of everyday reality seems to be anything but linear, and thus compressing it may help us make sense of it better. Fully exponential control characteristics are often criticised on musical terms however, as with a linear slope from a typical envelope generator, the rise time at the bottom is very slow, and the rise at the top is very fast. Equal loudness contours are obtained when driven by sine wave control signals.
2 Sinusoidal wavefolders complete the module, to be used in stereo or ganged.
Distortion performance is roughly -90dBc. All channels are DC coupled with offset at +/-5mV max per channel.