Overview

Cascade of second order Biquad filters

Discussion

A cascade of second order 5 multiply recursive filters. The module is designed to operate on multiple channels and applies the same coefficients across all channels. The state array is allocated to contain 4*numChannels*numStages values. Each 2nd order section implements the difference equation:

$y[n]=b_0x[n]+b_1x[n-1]+b_2x[n-2]-a_1y[n-1]-a_2y[n-2].$

The filter coefficients stored in the matrix .coeffs. This matrix is of dimension 5 x numStages and each column of the matrix corresponds to an individual 2nd order Biquad stage. Within each column, the coefficients are ordered as: $[b0; b1; b2; a1; a2].$

Type Definition

typedef struct _ModuleBiquadCascadeFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    INT32 numStages;                              // Number of stages in the filter. The filter order = 2 * numStages
    FLOAT32* coeffs;                              // Matrix of filter coefficients. The size of the matrix is 5 x numStages. Each column contains the variables for a biquad arranged as [b0; b1; b2; a1; a2].
    fract32* coeffsFract32;                       // Matrix of filter coefficients. The size of the matrix is 5 x numStages. Each column contains the variables for a biquad arranged as [b0; b1; b2; a1; a2].
    fract32* state;                               // State variables. 4 per channel.
    INT32* postShift;                             // Number of bits to shift
} ModuleBiquadCascadeFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
numStages	int	const	0	1	1:1:32
coeffs	float*	parameter	0	[5 x 1]	Unrestricted
coeffsFract32	fract32*	derived	1	[5 x 1]	Unrestricted
state	fract32*	state	1	[4 x 1]	Unrestricted
postShift	int*	derived	1	[1 x 1]	Unrestricted

Pins

Input Pins

Name: in

Description: audio input

Data type: fract32

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output