Filter Module

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Fig 1.0 Filter Module Diagram

The Filter Module allows the user to boost or remove frequencies from a signal. This module can also be used to boost or remove frequencies from a feedback loop.

Contents

Working with the Filter Module

Filter Types

2-Pole

This is a simple 2-Pole filter, which has lowpass, bandpass, and highpass modes. This filter is very light on CPU.

2-4 Pole

This is a 2-4 Pole filter, which has lowpass, bandpass, and highpass modes. The filter can morph between two and four poles by modifying the '2P-4P' parameter.

6-Pole Band

This filter consists of a highpass and a lowpass filter. The user sets the mid-point for both filters, the low width (the distance between the high pass filter cutoff frequency and the midpoint), and the high width (the distance between the low pass filter cutoff frequency and the midpoint). When the resonance of this filter is increased, it will have two separate resonant peaks. One peak at the cutoff frequency of the highpass filter, and another peak at the cutoff frequency of the lowpass filter.

Connecting the Filter Module

The Filter Module provides two typical AudioGL audio connections, which follow the same rules as any other audio connection.

The Filter Module can be used in Feedback Loops, as described in the Connections article.

Other Things

The 6-Pole Band filter is for all intensive purposes a different module. Because of this, when switching to this filter type, the Filter Module will be reset.

AudioGL's filters have the ability to self-oscillate. When boosting the resonance to high values, this may cause the filter to continue playing after a note has finished. This can be used as a tool to synthesize kick drums, or to create heavy distortion effects.

Parameters

'2-Pole' and '2-4 Pole' Filter Types

Parameter Range Description
Pitch / Resonance
0 to 1 in Y-Direction
0 to 140 in X-Direction

The Y-Direction controls the resonance of the filter.

The X-Direction controls the filter cutoff. Pitch values can be converted to frequencies using this chart.

LP-BP-HP
0 to 2

This parameter morphs the filter from a lowpass filter into a bandpass filter, or a highpass filter. At a level of '0', the filter will be a lowpass. At a level of '1', the filter will be a bandpass. Finally, at a level of '2', the filter will be a highpass.

2P-4P
0 to 2

This parameter morphs the filter from a 2-pole filter into a 4-pole filter. At a level of '0', the filter will be a 2-pole filter, and at a level of '1', the filter will be a 4-pole filter.

This parameter has no effect on the basic '2-Pole' filter type.

'6-Pole Bank' Filter Type

Parameter Range Description
Middle Point / Resonance
0 to 1 in Y-Direction
0 to 136 in X-Direction

The Y-Direction controls the resonance of the filter.

The X-Direction controls midpoint of the two filters used by this filter type. Pitch values can be converted to frequencies using this chart. To calculate cutoff frequencies, the values of the 'Low Width' and 'High Width' parameters must be taken into account.

Low Width
0 to 136

This parameter sets the distance between the midpoint, and the cutoff frequency of the highpass filter.

High Width
0 to 136

This parameter sets the distance between the midpoint, and the cutoff frequency of the lowpass filter.

Module Specific Options

Fig 3.0 Filter Module Options

The Filter Module has three buttons in it's popup menu, which allow you to switch between the different filter types listed above.

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