Overview

Cascade of second order Biquad filters with high precision implementation

Discussion

A cascade of second order recursive filters that are implemented using a high precision filter structure. The module is designed to operate on multiple channels and applies the same coefficients across all channels. The state array is allocated to contain 2*numChannels*numStages values. Filter coefficients should be mapped from SOS to Biquad representation [b0; b1; b2; a1; a2] and given in .coeffs. The leading a0 coefficient is not supplied and is assumed to equal 1.0. In the set function the coefficients will be mapped from Biquad form to High Precision representation [Fb; Gaa; Gab; K; Fa].

The filter coefficients are 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 _ModuleBiquadCascadeHP
{
    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].
    FLOAT32* targetCoeffs;                        // Matrix of filter coefficients in the High Precision format. The size of the matrix is 5 x numStages. Each column contains the variables for a biquad arranged as [Fb; Gaa; Gab; K; Fa].
    FLOAT32* state;                               // State variables. 2 per channel.
} ModuleBiquadCascadeHPClass;

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
targetCoeffs	float*	derived	0	[5 x 1]	Unrestricted
state	float*	state	1	[2 x 1]	Unrestricted

Pins

Input Pins

Name: in

Description: audio input

Data type: float

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output

Data type: float

MATLAB Usage

File Name: biquad_cascadeHP_module.m

 M=biquad_cascadeHP_module(NAME, NUMSTAGES)
 Creates a module that implements a cascade of second order Biquad
 stages. This module can be used to implement high order IIR filters.
 The module operates on multiple channels and uses the same set of
 coefficients across channels. This version uses a high precision implementation
 
 Arguments:
    NAME - name of the module.
    NUMSTAGES - number of biquad stages. The overall filter order
         is 2*NUMSTAGES.