Correlate

Overview

Cross correlation function

Discussion

This module computes the deterministic cross correlation of the signals on its input pins a block at a time. It is very similar to convolution, differing only in the order of the output. The output is computed by \(s[n] = \sum_{k=0}^{M-1} x[n+k] y[k]\), where \(x[n]\) is on pin 1 with length \(M\) and \(y[n]\) is on pin 2, also of length \(M\). This operation could be generalized to allow different block sizes if needed.

The parameters shape, skip and length allows control of the range of \(n\) that gets calculated. Shape is for quick setting of common ranges. shape = 0: sets skip=0, olen=2*M-1 to compute the full correlation shape = 1: sets skip=M/2, olen=M to compute the center part that has the same length as the inputs. shape = 2: leaves skip and olen to be user-defined. skip: starts storing output at \(n = \mathit{skip}\) olen: writes only this many output samples, so \(\mathit{skip} <= n < \mathit{skip} + \mathit{olen}\).

Module Pack

Advanced

ClassID

classID = 1244

Type Definition

typedef struct _ModuleCorrelate
{
ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
INT32 shape;                                  // Shape of subset to calculate
INT32 skip;                                   // Number of samples of full cross correlation to skip at output
INT32 olen;                                   // Length of output
} ModuleCorrelateClass;

Variables

Properties

Name	Type	Usage	Default Value	Range	Units
shape	int	parameter	0	0:2
skip	int	parameter	0	0:63	samples
olen	int	parameter	63	0:63	samples

Pins

Input Pins


Name	in0
Description	Input signal 0
Data type	float
Channel range	Unrestricted
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real


Name	in1
Description	Input signal 1
Data type	float
Channel range	Unrestricted
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real

Output Pins


Name	out
Description	Cross correlation output
Data Type	float

Matlab Usage

File Name: correlate_module.m 
 M = correlate_module(NAME, SHAPE) 
 This module implements a partial correlation of the two signals on its 
 input pins. How much of the correlation to write can be controlled by 
 the parameters. Also see convolve_module, which is very similar. 

 Arguments: 
   NAME - name of the module 
   SHAPE - enum of standard subset to calculate