OMF-1
Analog filter Rack
signal to be at full strength with no inversion of the signal. Fully counter clockwise
allows the signal to be at full strength but with inverted properties. The two types
actually sound identical on their own, but when mixed with the other two outputs
strange new filter sounds can be made.
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Smooth:
Output level of the four pole filter output. As with FIZZ, this is a reversible
attenuator.
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Mix Out:
Controls the wet/dry mix. That is it adjusts the ratio between the pre-
amplifier output and the output of the combined smooth and fizz signals. Set the Mix
Out pot to 'wet' to hear just the output of the filter. Set the pot to 'dry' to hear just the
output of the pre-amplified input signal with no filtering.
The Fizz, Smooth and Mix Out pots control the audio signal, and it will take a little bit of
practice to understand how these controls affect the final output signal. When each is used
on its own, the results are predictable enough. They act a simple level controls. However, by
mixing the signals together new and interesting effects can be heard. The simplest one to
try is setting the Mix Out to ‘wet’, the Smooth to full ‘+’ and the Fizz to full ‘-’. This creates a
simple band pass effect. What you will have here is not the traditional low pass filter sound,
but just one band of enhanced frequencies. You can sweep these up and down manually
with the filter frequency pot, or let the OMF do it all automatically with its many modulation
routes. At increased resonance, the output can become nothing like the original input signal.
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Peak:
This LED glows fiery red when the filter starts to clip. However, the ladder filter
actually sounds very good when over-driven, so this may be what you want.
Generally the GAIN pot should be set so that this LED just flickers occasionally when
in normal operation. For over-driven sounds it is usually best to stick with simple
monophonic input signals. Playing complex chords through an overloaded filter can
produce some very harsh sounds.
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Output:
The final output level is controlled by this pot. In normal use this pot would
normally be around the 1 o’clock position. However, this can be turned up to
give extra gain if you need it.
You should note that the peak LED only monitors the level going into the filter core
circuitry. It does not monitor the output of the module itself. The OMF's output
amplifier is designed to have an extra +10dB or so of gain. This allows for more
flexibility but it does mean that it is possible to overload and clip the output stage at
more extreme settings. This can be a useful source of new sounds but it can also
lead unwanted distortion. If the OMF sounds distorted and the peak LED is not lit
then you may need to back off the output level pot.
That completes the description of the audio controls at this stage. The rest of the pots and
switches control the envelope and low frequency oscillators. These form part of the control
circuitry and these will be described now.
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Control:
This is a simple two way switch that allows the filter’s processing circuitry to
be controlled by the main input or a second input, sometimes called the ‘side chain’.
The side chain input is never heard directly from the main output, but when selected
it will be able to control the envelope generator or follower.
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