WindowAlias

Overview

Applies a time domain window and optionally aliases the result to a shorter length

Discussion

This module applies a time domain window to a signal and then optionally aliases the result. This operation is useful prior to taking the FFT of a signal and commonly occurs in STFT-based filterbanks. The module operates on multiple channels with all channels having the same window and aliasing operation applied. The length of the window (WLEN) and the size of the output (OLEN) are specified at instantiation time. If OLEN == WLEN, then no aliasing occurs and the module simply applies a window. For aliasing, set WLEN equal to a multiple of OLEN. This causes the window to be applied and the result to be time aliased to OLEN samples. WLEN must be a multiple of OLEN so that an integer number of complete blocks are aliased.

The module outputs a block of size [OLEN numChannels], where numChannels equals the number of channels in the input signal. This block is output everytime that the module's processing function is called.

The window coefficients are set to a Hanning window (raised cosine) at instantiation time. The window coefficients may subsequently be changed.

Module Pack

Advanced

ClassID

classID = 1355

Type Definition

typedef struct _ModuleWindowAlias
{
ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
INT32 winLen;                                 // Length of the window
INT32 stateIndex;                             // Index of the oldest state variable in the array of state variables
INT32 numAliasSections;                       // Number of sections that are aliased to form the output.  Equals WLEN/OLEN
FLOAT32* window;                              // Window coefficients
FLOAT32* state;                               // State variable array
} ModuleWindowAliasClass;

Variables

Properties

Name	Type	Usage	isHidden	Default Value	Range	Units
winLen	int	const	0	256	1:1:8192	samples
stateIndex	int	state	1	0	Unrestricted
numAliasSections	int	const	1	1	Unrestricted
window	float*	parameter	0	[256 x 1]	Unrestricted
state	float*	state	1	[256 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: window_alias_module.m 
 M=window_alias_module(NAME, WLEN, OLEN) 
 Creates a module which applies a window and optionally aliases the 
 result to a shorter length.  Arguments: 
    NAME - name of the module. 
    WLEN - length of the window to apply. 
    OLEN - output sequence length after aliasing. 

 This module is often used as part of a short term Fourier transform 
 filterbank.  The module operates on an arbitrary number of channels 
 with the same window and length parameters applied.  If you set 
 WLEN = OLEN, then no aliasing occurs.