SVF

Overview

State Variable Filter with coefficients derived from input pins

Discussion

This module is a State Variable Filter (short "SVF") module using the standard Chamberlin algorithm which implements a number of standard filter types. The filter operates on multiple interleaved channels, with all channels being processed by the same set of coefficients.

After specifying filterType, adjust the filter parameters by setting the fields, gain, frequency and quality. Frequency, gain and quality can be controlled either through respective input control pin or from the module inspector. Some filter parameters are not applicable to all filter types. The variable, frequency controls the center frequency of the filter, gain determines the boost or cut in dB, and quality determines how sharp the filter is. Low quality values lead to broad filters and high quality values lead to narrow filters.

The following table discusses the various filter types and which variables are active in each case.

filterType=0, Simple pass through with unity gain.

filterType=1, high pass filter. [frequency].

filterType=2, low pass filter. [frequency].

filterType=3, all pass filter. [frequency].

filterType=4, high pass filter 2. [frequency, quality].

filterType=5, low pass filter 2. [frequency, quality].

filterType=6, all pass filter 2. [frequency, quality].

filterType=7, bandpass filter. It has unity gain at the specified frequency and falls off in both directions. The bandwidth of the filter is determined by quality. [frequency, quality, gain].

filterType=8, bandpass filter normalized. It has unity gain at the specified frequency and falls off in both directions. The bandwidth of the filter is determined by quality. [frequency, quality, gain].

filterType=9, notch filter. It has unity gain except around the specified frequency. At the specified frequency, the filter has a true notch with -inf dB gain. [frequency, quality].

filterType=10, peak (bell) filter. [frequency, quality, gain].

filterType=11, peak (bell) filter with variable quality. [frequency, quality, gain].

filterType=12, asymmetrical low shelf. [frequency, quality, gain].

filterType=13, asymmetrical hi shelf. [frequency, quality, gain].

filterType=14, tilt filter [frequency, quality, gain].

When the parameters frequency, gain or quality are controlled through the input pin, then the default behaviour of the module is to calculate coefficients in the Set function. User can change the behaviour through the parameter setBehavior to calculate coefficients in the Process function itself.

Module Pack

awe-mod-dspc-snd

ClassID

classID = 41804

Type Definition

typedef struct _ModuleSVF
{
ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
INT32 filterType;                             // Selects the type of filter that is implemented by the module.
INT32 setBehavior;                            // Controls the Set function calling behavior of the module. 0 = OnChangeDeferredSet, 1 = OnChangeInstantSet
FLOAT32 frequency;                            // Cutoff frequency of the filter, in Hz.
FLOAT32 gain;                                 // Amount of boost or cut to apply, in dB if applicable.
FLOAT32 quality;                              // Specifies the Q of the filter, if applicable.
FLOAT32 g;                                    // g coefficient
FLOAT32 g1;                                   // g1 coefficient
FLOAT32 h;                                    // h coefficient
FLOAT32 cLp;                                  // LP factor
FLOAT32 cBp;                                  // BP factor
FLOAT32 cHp;                                  // HP factor
INT32 updateActive;                           // Specifies whether the filter coefficients are updating (=1) or fixed (=0).
FLOAT32 current_g;                            // Instantaneous g coefficient.
FLOAT32 current_g1;                           // Instantaneous g1 coefficient.
FLOAT32 current_h;                            // Instantaneous h coefficient.
FLOAT32 current_cLp;                          // Instantaneous cLp coefficient.
FLOAT32 current_cBp;                          // Instantaneous cBp coefficient.
FLOAT32 current_cHp;                          // Instantaneous cHp coefficient.
UINT32 pinID;                                 // Specifies which control pins are available.
FLOAT32* state;                               // State variables. 2*numChannels per section.
} ModuleSVFClass;

Variables

Properties

Name	Type	Usage	isHidden	Default Value	Range	Units
filterType	int	parameter	0	0	0:14
setBehavior	int	parameter	0	0	0:1
frequency	float	state	0	250	10:23990	Hz
gain	float	state	0	0	-24:24	dB
quality	float	state	0	0.7071	0.05:20
g	float	derived	0	1	Unrestricted
g1	float	derived	0	0	Unrestricted
h	float	derived	0	0	Unrestricted
cLp	float	derived	0	0	Unrestricted
cBp	float	derived	0	0	Unrestricted
cHp	float	derived	0	0	Unrestricted
updateActive	int	parameter	1	0	0:1
current_g	float	state	1	0	Unrestricted
current_g1	float	state	1	0	Unrestricted
current_h	float	state	1	0	Unrestricted
current_cLp	float	state	1	0	Unrestricted
current_cBp	float	state	1	0	Unrestricted
current_cHp	float	state	1	0	Unrestricted
pinID	uint	const	1	7	Unrestricted
state	float*	state	1	[2 x 1]	Unrestricted

Pins

Input Pins


Name	freqPin
Description	Cutoff frequency of the filter
Data type	float
Channel range	1
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real


Name	gainPin
Description	Gain of the filter
Data type	float
Channel range	1
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real


Name	qPin
Description	Q of the filter
Data type	float
Channel range	1
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real


Name	in
Description	Input signal
Data type	float
Channel range	Unrestricted
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real

Output Pins


Name	out
Description	Output signal
Data Type	float

Matlab Usage

File Name: svf_module.m