- Low Pass
- Controls the cutoff frequency of the low-pass filter
- High Pass
- Controls the cutoff frequency of the high-pass filter
The Noise and Filter module is used to generate non pitched sounds such as wind and surf noises. It features two separate tunable filters, one high pass and one low pass, which may be used separately to process other sources. Two types of noise output are provided. White noise which when unfiltered sounds like gas escaping, and pink noise which sounds more like a big waterfall. The module also gives a very low frequency output or infra-red signal. This can be heard as a serious of random thumps when listened too, but it is actually a randomly varying output voltage changing all the time, sometimes quickly and sometimes hardly at all. Fascinating to watch when it controls an LED, but it comes into its own when controlling filter cut-off on an otherwise static sound.
The noise source is true analogue, a reverse biased PNP transistor. However, room is given on the PCB for zeners and other devices should you decide to experiment.
The filters are one pole passive designs similar in topology to the later Moog modular. I have used 47K reverse log pots as the variable element in both the high and low pass filters. These pots have been especially made for Oakley Sound Systems by Omeg. One pole filters sound particularly nice with audible noise, and give far more natural wind and surf sounds than the usual 2 or 4 pole filters. They are not voltage controllable.