Overview

2nd order IIR filter

Discussion

Second order 5 multiply recursive filter with algorithm precision selectable. Precision type 0 uses 24x24 with 56-bit accumulator, 1 uses 32x32 with 32-bit accumulator, 2 uses 32x32 with 64-bit accumulator and 3 uses 24x24 with 24-bit accumulator. 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 values. The frequency response of the module is determined by the values of the 5 coefficients, and the coefficients come directly from the MATLAB second order representation. The leading a0 coefficient is not supplied and is assumed to equal 1.0. The module implements the difference equation:

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

Type Definition

typedef struct _ModuleBiquadV2Fract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    INT32 precisionType;                          // Boolean value that determines whether all channels are summed to form a single output.
    INT32 updateActive;                           // Specifies whether the filter coefficients are updating (=1) or fixed (=0).
    INT32 postShift;                              // Number of bits to shift
    INT32 bShift;                                 // Number of bits to shift of Numerator coefficients
    INT32 currentBShift;                          // Current post shift of Numerator coefficients
    INT32 aShift;                                 // Number of bits to shift of Denominator coefficients
    INT32 currentAShift;                          // Current post shift of Denominator coefficients
    FLOAT32* coeffs;                              // coefficients
    fract32* coeffsFract32;                       // coefficients in Fract32
    fract32* state;                               // State variables. 6 per channel.
    fract32* currentCoeffsFract32;                // Current coefficients in Fract32
} ModuleBiquadV2Fract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
precisionType	int	const	0	0	Unrestricted
updateActive	int	state	0	1	0:1
postShift	int	parameter	1	2	Unrestricted
bShift	int	derived	1	1	Unrestricted
currentBShift	int	state	1	3	Unrestricted
aShift	int	derived	1	1	Unrestricted
currentAShift	int	state	1	2	Unrestricted
coeffs	float*	parameter	0	[5 x 1]	Unrestricted
coeffsFract32	fract32*	derived	0	[5 x 1]	Unrestricted
state	fract32*	state	1	[6 x 1]	Unrestricted
currentCoeffsFract32	fract32*	state	0	[5 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

Data type: fract32

MATLAB Usage

File Name: biquad_v2_fract32_module.m

 M=biquad_v2_fract32_module(NAME, TYPE)
 Creates a second order IIR filter Fract32 (biquad) for use with the Audio
 Weaver.  Arguments:
     NAME - name of the module.
     TYPE - Precision type. 0 - 24x24 with 56-bit Acc
                            1 - 32x32 with 32-bit Acc
                            2 - 32x32 with 64-bit Acc
                            3 - 24x24 with 24-bit Acc