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(8.D.2.7) Correlate

(8.D.2.7) 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 $\mathit{skip} <= n < \mathit{skip} + \mathit{olen}$.

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

isHidden

Default value

Range

Units

shape

int

parameter

0

0

0:2

 

skip

int

parameter

0

0

0:63

samples

olen

int

parameter

0

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

 

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