# Precedence-based cross-correlograms (Scripts) 1.0

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## Precedence-based cross-correlograms (Scripts) Publisher's description

### CH_XCORR Calculate cross-correlograms with a wide range of options

CH_XCORR Calculate cross-correlograms with a wide range of options.

SYNTAX

CCG = CH_XCORR(HC_L,HC_R,FRAME_LENGTH,NOVERLAP,MAXLAG,TAU)
CCG = CH_XCORR(...,INHIB)
CCG = CH_XCORR(...,IC_T,NORM_FLAG)
CCG = CH_XCORR(...,INHIB_MODE)
[CCG,IC] = CH_XCORR(...)

DESCRIPTION

CCG = CH_XCORR(HC_L,HC_R,FRAME_COUNT,FRAME_LENGTH,MAXLAG,TAU) calculates cross-correlograms with a range of cross-correlation parameters.

The function cross-correlates the input 2-D matrices HC_L and HC_R over frames of length FRAME_LENGTH. It is assumed that the number of frequency channels is min(size(HC_L)) and hence HC_L and HC_R can be in either orientation. The cross-correlograms consist of cross-correlations for every frame and frequency channel. The function calculates running cross-correlations for every sample and integrates these cross-correlations over NOVERLAP frames. The lags are determined by MAXLAG and the cross-correlation is computed over the range of lags -MAXLAG to MAXLAG, i.e., 2*MAXLAG+1 lags. The number of frames FRAME_COUNT is calculated thus:

FRAME_COUNT = floor((max(size(HC_L))-MAXLAG-1)/(FRAME_LENGTH))-NOVERLAP+1;

The underlying cross-correlation algorithm is based on that proposed by Faller & Merimaa [1]. In this implmentation, the time constant of the backward infinite exponential window is given by TAU (in samples).

CCG = CH_XCORR(...,INHIB) multiplies the running cross-correlations with INHIB before the cross-correlations are averaged. If INHIB is un-specified it is set to ones(size(HC_L)).

CCG = CH_XCORR(...,IC_T,NORM_FLAG) allows an IC threshold to be specified and normalisation to be turned on and off. The algorithm calculates Interaural Coherence (IC) according to [1]. The cross-correlogram is calculated for each frame by averaging only those cross-correlations within the frame for which the corresponding IC exceeds the IC threshold IC_T (0<=IC_T<=1). Setting this value to 0 will result in all cross-correlations contributing to the average (default). This implementation also permits the normalisation to be turned off by specifying NORM_FLAG; a non-zero value means normalisation will be applied (default). This means, for example, that an IC theshold could be employed, but the un-normalised cross-correlations would contribute to the cross-correlograms. Note that either both or neither of these values must be specified.

CCG = CH_XCORR(...,INHIB_MODE) uses the mode INHIB_MODE to apply the inhibition. The options are 'multiply' (default), whereby the inhibitory signal INHIB will be multiplied with the running cross-correlation, or 'subtract', whereby INHIB will be subtracted from the running cross-correlation.

[CCG,IC] = CH_XCORR(...) returns the calculated IC to the matrix IC. Although the matrix returned is the same size as HC_L, IC is only calculated for samples 1:FRAME_COUNT*FRAME_LENGTH, other values will
be set to 0.

ALGORITHM

See the enclosed documentation for more details on the workings of the algorithm and an important caveat.

REFERENCES

[1] C. Faller and J. Merimaa, "Source localization in complex listening situations: Selection of binaural cues based on interaural coherence", The Journal of the Acoustical Society of America, vol. 116, pp.3075-3089, Nov. 2004.

C. Hummersone, R. Mason, and T. Brookes, "A comparison of computational precedence models for source separation in reverberant environments", in 128th Audio Engineering Society Convention, London, May 2010, paper 7981.

#### System Requirements:

MATLAB 7.8 (R2009a)
Program Release Status: New Release
Program Install Support: Install and Uninstall

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