NICK'S WORLD OF SYNTHESIZERS
VALVE FILTER
This is 3 valve filters wired in parallel, 2 bandpass and one that is switchable from lowpass to highpass. The Q is adjustable from subtle to oscillation.
The individual cutoff frequencies for each filter can be swept at the same time, in different directions and by different amounts. This sweeping is done by turning the master sweep knob. Each filter has 1 knob to set what its cutoff frequency will be when the master sweep knob is at the start position and one to set the cutoff frequency at the end position of the master sweep knob.
The result is very rich complicated filtering. This is further enhanced by imperfections of the valve design. There is lots of soft distortion and cross-talk between the 3 filters. Because the cross-talk is in both directions, it results in chaotic behaviour. The chaos is nice and subtle when the Q is low, and quite extreme when all 3 filters are oscillating. The oscillating filters lock on to the harmonics of the other filters.
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