Cross-correlation (crosscorrelationProc.m
)¶
The IHC representations of the left and the right ear signals is used to
compute the normalised CCF in the FFT domain for short time frames of
cc_wSizeSec
duration with a step size of cc_hSizeSec
. The CCF is
normalised by the auto-correlation sequence at lag zero. This normalised CCF
is then evaluated for time lags within cc_maxDelaySec
(e.g., [-1 ms, 1 ms])
and is thus a three-dimensional function of time frame, frequency channel and
lag time. An overview of all CCF parameters is given in
Table 32. Note that the choice of these parameters will
influence the computation of the ITD and the IC processors, which are
described in Interaural time differences (itdProc.m) and
Interaural coherence (icProc.m), respectively.
Parameter | Default | Description |
---|---|---|
cc_wname |
'hann' |
Window type |
cc_wSizeSec |
0.02 |
Window duration in s |
cc_hSizeSec |
0.01 |
Window step size in s |
cc_maxDelaySec |
0.0011 |
Maximum delay in s considered in CCF computation |
The script DEMO_Crosscorrelation.m
demonstrates the functionality of the
CCF function and the resulting plots are shown in Fig. 37. The left
panel shows the ear signals for a speech source that is located closer to the
right ear. As result, the left ear signal is smaller in amplitude and is delayed
in comparison to the right ear signal. The corresponding CCF is shown in the
right panel for 32 auditory channels, where peaks are centred around positive
time lags, indicating that the source is closer to the right ear. This is even
more evident by looking at the SCCF, as shown in the bottom right panel.