Version 1 Filters
The Transfer function - Poles or
The relationship between what goes into a filter at one end and what comes out at the other is known as the 'Transfer function'. This is commonly described in terms of decibels per octave, and occasionally as a number of 'poles'. The decibel per octave terminology refers to the amount of reduction in gain of the signal as the frequency rises by an octave. As an attenuation of 6 decibels (db) is the equivalent of a halving of the gain, filter transfer functions are referred to in units of 6db/octave.
This can also be referred to in terms of 'Poles' where one pole is equivalent to a transfer function of 6db/octave. Hence a 2 pole filter is the same as a 12db/octave filter, a 4 pole the same as a 24db/octave filter, and so on.
The most common types of filter are:
Low Pass - Higher frequencies are attenuated whilst lower ones are allowed to pass through 'untouched'.
High Pass - Low frequencies are attenuated whilst high ones are allowed through untouched.
Band Pass - Both low and High frequencies are attenuated, leaving just a 'band' in the middle to pass through unaffected.
Band Reject - also known as a Notch Filter - the opposite of a Band Pass filter - the high and low frequencies are unaffected, whilst the central frequencies are attenuated.
Comb Filter - This attenuates a number of separate bands of frequencies and can be envisaged like a comb viewed from the side. Although not found in version 1 of the modular, there is a Comb Filter in version 2.
Cut Off - Each filter has a Cut Off control. This determines the frequency at which the filter starts to take effect - in a Low pass filter, for example, it determines the frequency above which the filter will start to attenuate the signal. To be completely accurate, the Cut Off frequency is the frequency at which the signal is already accentuated by 3db.
Resonance - Each filter also has a control for Resonance. Filters don't just attenuate the frequencies defined by the Cut Off control - they also boost certain frequencies around the Cut off point, and this is referred to as resonance. The resonance control alters the amount of accentuation that is given to the signal around the cut off point.
Setting the Resonance at it's maximum point can easily result in what is known as self-oscillation - a point at which the resonance of the filter starts to feedback on itself. This can create some powerful tones which have very little to do with the signal that is being fed into the filter, and an awful lot to do with the nature of the filter itself. When a filter self oscillates, it may be possible to 'play' the filter as if it were actually an Oscillator itself.
Modulation - All of the filters have a number of Modulation inputs which can be used to dynamically control the Cut Off frequency of the filter. A few of the filters also have a ResMod control, which can be used to modulate the Resonance of the Filter.
2-Pole Multi Mode
|12 db/Octave filter with 3 Cutoff frequency modulation inputs and a choice of Low, High or Band pass filter outputs.|
|2-Pole Multi Mode 2||
|Bug fixed version of the above - Cutoff Zipper noise is suppressed and Modulation works even if Cutoff is turned all the way down.|
|4-Pole High Pass||
|24db/Octave High Pass filter. 3 mod inputs for Cutoff modulation.|
|4-Pole Low Pass||
|24db/Octave Low Pass filter. 3 mod inputs for Cutoff modulation.|
|4-Pole Low Pass V||
|A 'vintage' version of the above, in which the level of the original signal remains unchanged, regardless of the Resonance setting. 3 mod inputs for Cutoff modulation.|
4-Pole Low Pass V - ResMod
|As above, but with a Modulation input for the Resonance amount, and only 2 Mod ins for the Cutoff frequency.|
|8-Pole Band Pass||
|Attenuates the high and low frequencies, letting a central band through untouched - Cut Off determines the central frequency around which the Band is determined. 3 Mod inputs for Cutoff frequency.|
|18dB Low Pass|
|18db/Octave Low Pass filter. 3 mod inputs for Cutoff modulation.|
|Uknow Low Pass|
|12db/Octave Low Pass filter as used in the Pulsar Uknow 007 synth, which is modelled on the highly popular Juno 106. The filters are very closely modelled on the original.|
|Uknow Low Pass - ResMod|
|As above, but with a Modulation input for the Filter Resonance.|
|Uknow Low Pass/High Pass - ResMod|
As above, but with an additional (non-resonant) High Pass filter. The Resonance knob and all modulation inputs control resonance for the low-pass filter only. There is a separate control for the Cut off of the High Pass filter.
|Fixed Filter Bank|
|Filter with 11 separate bands with cut/boost controls for each frequency band, and a seperate gain control for the whole filter. You'll find this in the 'Effects' folder, not the Filters, for some reason.|
One day, one day...