The precedence effect describes the ability of humans to fuse and localize the sound based on the first-arriving parts, in the presence of its successive version with a time delay below an echo-generating threshold [Wallach1949]. The effect of the later-arriving sound is suppressed by the first part in the localization process. The precedence effect processor in |AFE| models this, with the strategy based on the work of [Braasch2013]. The processor detects and removes the lag from a binaural input signal with a delayed repetition, by means of an autocorrelation mechanism and deconvolution. Then it derives the |ITD| and |ILD| based on these lag-removed signals.
The input to the precedence effect processor is a binaural time-frequency signal chunk from the gammatone filterbank. Then for each chunk a pair of |ITD| and |ILD| values is calculated as the output, by integrating the |ITD|s and |ILD|s across the frequency channels according to the weighted-image model [Stern1988], and through amplitude-weighted summation. Since these |ITD|/|ILD| calculation methods of the precedence effect processor are different from what are used for the |AFE| |ITD| and |ILD| processors, the |AFE| |ITD| and |ILD| processors are not connected to the precedence effect processor. Instead the steps for the correlation analyses and the |ITD|/|ILD| calculation are coded inside the processor as its own specific techniques. :numref:`tab-precedence` lists the parameters needed to operate the precedence effect processor.
’precedence’.
| Parameter | Default | Description |
|---|---|---|
prec_wSizeSec |
20E-3 |
Window duration in s |
prec_hSizeSec |
10E-3 |
Window step size in s |
prec_maxDelaySec |
10E-3 |
Maximum delay in s for autocorrelation computation |
:numref:`fig-precedence` shows the output from a demonstration script
DEMO_precedence.m. The input signal is a 800-Hz wide bandpass noise of 400
ms length, centered at 500 Hz, mixed with a reflection that has a 2 ms delay,
and made binaural with an |ITD| of 0.4 ms and a 0-dB |ILD|. During the
processing, windowed chunks are used as the input, with the length of 20 ms. It
can be seen that after some initial confusion, the processor estimates the
intended |ITD| and |ILD| values as more chunks are analyzed.
Left panel: band-pass input noise signal, 400 ms long (only the first 50 ms is shown), 800 Hz wide, centered at 500 Hz, mixed with a reflection of a 2-ms delay, and made binaural with an of 0.4 ms |ITD| and |ILD| of 0 dB. Right panel: estimated |ITD| and |ILD| shown as a function of time frames.
| [Braasch2013] | Braasch, J. (2013), “A precedence effect model to simulate localization dominance using an adaptive, stimulus parameter-based inhibition process.” The Journal of the Acoustical Society of America 134(1), pp. 420–35. |
| [Stern1988] | Stern, R. M., Zeiberg, A. S., and Trahiotis, C. (1988), “Lateralization of complex binaural stimuli: A weighted-image model,” The Journal of the Acoustical Society of America 84(1), pp. 156–165, http://scitation.aip.org/content/asa/journal/jasa/84/1/10.1121/1.396982. |
| [Wallach1949] | Wallach, H., Newman, E. B., and Rosenzweig, M. R. (1949), “The Precedence Effect in Sound Localization,” The American Journal of Psychology 62(3), pp. 315–336, http://www.jstor.org/stable/1418275. |