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Thinning periodicity detectors for modulated pulse streams.
Patterson, R.D. & Nimmo-Smith, I.
In B.C.J. Moore & R.D. Patterson (Eds.), Auditory Frequency Selectivity (pp.299-307), NATO ASI Series A: Life Sciences, Vol. 19. New York: Plenum Publishing Corporation.
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The purpose of this paper is to define the periodicity detector suggested by the alignment of pulses on a spoke in the spiral processor, and to compare its efficiency with that of more familiar detectors. We begin with the most familiar, a discrete ‘cosine’ detector, and determine its response to a set of four modulated pulse streams that have varying amounts of carrier and modulation information. Relative to the number of elements in the detector the discrete cosine proves inefficient, particularly with regard to modulation information. The analysis reveals that, since the input is known to be a pulse stream, some of the detector elements are redundant. Accordingly, we proceed to define three more detectors by successively thinning the cosine detector, that is, by successively removing sets of redundant elements. The efficiency of the thinned detectors is then checked by calculating their responses to the same set of modulated pulse streams. The chain of definition and evaluation converges on a ‘log2 periodic’ detector which is the one underlying the spiral processor.