BiquadSmoothedFract32

Overview

2nd order smoothly updating IIR filter

Discussion

Smoothly varying 5 coefficient biquad filter. 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 is similar to the unsmoothed Biquad module, except that the filter coefficients are smoothed on a block-by-block basis. The module contains two sets of filter coefficients: [b0, b1, b2, a1, a2] are the "target" coefficients that serve as control variables to the module. The coefficients [current_b0, current_b1, current_b2, current_a1, current_a2] are the instantaneous coefficients that are updated on a block by block basis using exponential smoothing. The current coefficients exponentially approach the control coefficients. The instance variable.updateActive is a Boolean controls whether the coefficient smoothing occurs at the start of each block. .updateActive was provided to allow the coefficient smoothing to be halted and the target coefficients updated atomically.

The rate of smoothing is controlled by the .smoothingTime instance variable.

Module Pack

Standard

ClassID

classID = 134

Type Definition

typedef struct _ModuleBiquadSmoothedFract32
{
ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
INT32 updateActive;                           // Specifies whether the filter coefficients are updating (=1) or fixed (=0)
FLOAT32 smoothingTime;                        // Time constant of the smoothing process
fract32 smoothingCoeff;                       // Smoothing coefficient.  This is computed based on the smoothingTime, sample rate, and block size of the module
INT32 postShift;                              // Number of bits to shift
INT32 currentPostShift;                       // Current post shift
FLOAT32* coeffs;                              // Desired coefficients
fract32* coeffsFract32;                       // Desired coefficients in fract32
fract32* current_coeffsFract32;               // Instantaneous coefficients
fract32* state;                               // State variables.  4 per channel.
} ModuleBiquadSmoothedFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default Value	Range	Units
updateActive	int	parameter	0	1	0:1
smoothingTime	float	parameter	0	10	0:1000	msec
smoothingCoeff	fract32	derived	1	0.064493	Unrestricted
postShift	int	derived	1	1	Unrestricted
currentPostShift	int	state	1	1	Unrestricted
coeffs	float*	parameter	0	[5 x 1]	-10:10	linear
coeffsFract32	fract32*	derived	1	[5 x 1]	Unrestricted
current_coeffsFract32	fract32*	state	0	[5 x 1]	Unrestricted
state	fract32*	state	1	[4 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_smoothed_fract32_module.m 
 M=biquad_smoothed_fract32_module(NAME) 
 Creates a second order IIR Fract32 filter (biquad_smoothed) for use with the 
 Audio Weaver.  This filter smoothly updates its coefficients on a block 
 by block basis. 
    NAME - name of the module.