Overview

Sparse FIR filter which works together with the DelayStateWriter module

Discussion

This module implements a sparse FIR filter which is also known as a tapped delay line. This module stores only the coefficients and delay times and works in conjunction with an upstram delay_state_writer_module.m. The delay_state_writer_module.m holds the state variables and can be shared by multiple FIRSpareReaderModules.

You need to make sure that the maximum tapped delay time does not exceed the allocated size of the upstream state buffer. No checking is made at run-time that this is the case.

The module only outputs a mono channel of data and the output blockSize must be a multiple of 8 samples. This last condition is checked by the module's prebuild function.

Type Definition

typedef struct _ModuleFIRSparseReader
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    INT32 numTaps;                                // Number of non-zero coefficients (taps) in the filter
    INT32 dswObjectID;                            // Object ID of the upstream DelayStateWriter module
    INT32* tapDelay;                              // Current delay per tap
    INT32* tapDelayTarget;                        // Current delay per tap
    FLOAT32* tapCoeffs;                           // Coefficient applied to each tap output
    void * dswObjectPtr;                          // Points to the upstream DelayStateWriter module
} ModuleFIRSparseReaderClass;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
numTaps	int	const	0	20	Unrestricted
dswObjectID	int	state	1	-1	Unrestricted
tapDelay	int*	parameter	0	[20 x 1]	Unrestricted	samples
tapDelayTarget	int*	state	0	[21 x 1]	Unrestricted	samples
tapCoeffs	float*	parameter	0	[20 x 1]	Unrestricted
dswObjectPtr	void *	state	1		Unrestricted

Pins

Input Pins

Name: ID

Description: audio input

Data type: int

Channel range: 1

Block size range: 1

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output

Data type: float

Scratch Pins

Channel count: 1

Block size: 32

Sample rate: 48000

MATLAB Usage

File Name: fir_sparse_reader_module.m

 M = fir_sparse_reader_module(NAME, NUMTAPS, BLOCKSIZE, SAMPLERATE)
 Creates a sparse FIR filter which is equivalent to a multi-tap time
 delay in which the outputs are weighted and summed.  This module works
 in conjunction with the delay_state_writer_module.m.  The "writer"
 module stores the circular state buffer while this "reader" module
 does the actual processing.  The "writer" module output is a pointer
 to its instance structure.  The "reader" module uses the instance
 pointer to read data out of the state buffer.
 This module can only process a single mono channel of data.
 Arguments:
    NAME - name of the module.
    NUMTAPS - number of taps
    BLOCKSIZE - output block size (number of samples to generate).
        If this is empty then we use the blockSize from the system
        input.  By default, BLOCKSIZE = [].
    SAMPLERATE - sample rate of the output data.  If this is empty
        then we use the sample rate of the first input pin of the
        containing system.  By default, SAMPLERATE = [].