Synchrony capture filterbank: Auditory-inspired signal processing for tracking individual frequency components in speech

Abstract

A processing scheme for speech signals is proposed that emulates synchrony capture in the auditory nerve. The role of stimulus-locked spike timing is important for representation of stimulus periodicity, low frequency spectrum, and spatial location. In synchrony capture, dominant single frequency components in each frequency region impress their time structures on temporal firing patterns of auditory nerve fibers with nearby characteristic frequencies (CFs). At low frequencies, for voiced sounds, synchrony capture divides the nerve into discrete CF territories associated with individual harmonics. An adaptive, synchrony capture filterbank (SCFB) consisting of a fixed array of traditional, passive linear (gammatone) filters cascaded with a bank of adaptively tunable, bandpass filter triplets is proposed. Differences in triplet output envelopes steer triplet center frequencies via voltage controlled oscillators (VCOs). The SCFB exhibits some cochlea-like responses, such as two-tone suppression and distortion products, and possesses many desirable properties for processing speech, music, and natural sounds. Strong signal components dominate relatively greater numbers of filter channels, thereby yielding robust encodings of relative component intensities. The VCOs precisely lock onto harmonics most important for formant tracking, pitch perception, and sound separation.

Improved Auditory-Inspired Signal Processing Algorithm Design for Tracking Multiple Frequency Components

“…The frequency-following behavior of the adaptive filters of the SCFB is analogous to frequency capture of the auditory nerve fibers (ANFs) by their preferential phaselocking to dominant, nearby frequency components, called "synchrony capture." The phenomenon of synchrony capture and its relation to SCFB architectures were introduced and discussed more thoroughly in our previous paper [21]. Briefly, synchrony capture refers to the tendency of an ANF to phase-lock exclusively to one cochlear-resolved dominant frequency component or to groups of unresolved components.…”

“…3. It is a modified version of the previously proposed SCFB algorithm [21]. The original SCFB algorithm consisted of a bank of broadly tuned filters in cascade…”

“…These triplet BPFs are embedded in a feedback control loop. The resulting structure can adaptively lock onto locally dominant frequency components, tracking individual frequency components at low frequencies and the dominant carrier frequency of modulated frequency components at higher frequencies [21].…”

“…In this paper, we propose an improved frequency tracking algorithm based on the previously proposed auditoryinspired synchrony capture filterbank (SCFB) [21]. The original SCFB algorithm consisted of a bank of broadly tuned filters in cascade with narrower stagger-tuned triplet filters, that form part of a frequency discriminator loop (FDL).…”

“…1. This paper focuses on improvements to our original frequency tracking algorithm [21]. For greater ease of implementation, the SCFB signal processing architecture is presented primarily in a tutorial format.…”