Authors: Öğütnaz Çoban¹, Mustafa Yüksel¹
¹Ankara Medipol University
Introduction: Cochlear implant (CI) sound processing strategies on the preservation of timbral features in music. Specifically, we compared simulations of traditional Continuous Interleaved Sampling (CIS), Fine Structure Processing (FSP), and the Harmonic Single Sideband Encoder (HSSE) strategy. The aim was to determine how well these strategies retain critical acoustic dimensions—spectral centroid, spectral flux, spectral irregularity, and log attack time—when compared to unprocessed (UP) sounds. These parameters have been identified as key predictors of timbre perception in both normal-hearing listeners and CI users and are frequently used in studies examining musical sound quality and auditory object identification.
Methods: Eight instrument sounds from the CAMP timbre subtest were processed in MATLAB using CIS, FSP, and HSSE simulations. Four acoustic descriptors were extracted for each condition: spectral centroid (SC), spectral flux (SF), spectral irregularity (SI), and log attack time (LAT). Paired t-tests compared processed versus unprocessed signals.
Results: No significant difference was found in SC across strategies (p > 0.05), though FSP approached significance (p = 0.060). All strategies significantly altered SF (p < 0.001). For SI, only HSSE did not differ from UP (p = 0.668); CIS and FSP showed significant reductions (p < 0.001). No significant differences were observed for LAT in any strategy (p > 0.05).
Conclusion: CI processing strategies differ in their ability to preserve specific timbral features. While spectral flux was consistently altered, HSSE uniquely preserved spectral irregularity at a level comparable to natural sound. These findings support prior research showing that CI users rely more on envelope cues due to reduced access to fine spectral structure. Among the tested methods, HSSE appears to provide the most balanced representation of both spectral and temporal components of musical timbre.
Keywords: Cochlear implant, sound processing strategies, temporal fine structure, timbre perception, spectral centroid, spectral flux
