Semitone frequency mapping to improve music representation for nucleus cochlear implants

Abstract

The frequency-to-channel mapping for Cochlear implant (CI) signal processors was originally designed to optimize speech perception and generally does not preserve the harmonic structure of music sounds. An algorithm aimed at restoring the harmonic relationship of frequency components based on semitone mapping is presented in this article. Two semitone (Smt) based mappings in different frequency ranges were investigated. The first, Smt-LF, covers a range from 130 to 1502 Hz which encompasses the fundamental frequency of most musical instruments. The second, Smt-MF, covers a range from 440 to 5040 Hz, allocating frequency bands of sounds close to their characteristic tonotopical sites according to Greenwood's function. Smt-LF, in contrast, transposes the input frequencies onto locations with higher characteristic frequencies. A sequence of 36 synthetic complex tones (C3 to B5), each consisting of a fundamental and 4 harmonic overtones, was processed using the standard (Std), Smt-LF and Smt-MF mappings. The analysis of output signals showed that the harmonic structure between overtones of all complex tones was preserved using Smt mapping. Semitone mapping preserves the harmonic structure and may in turn improve music representation for Nucleus cochlear implants. The proposed semitone mappings incorporate the use of virtual channels to allow frequencies spanning three and a half octaves to be mapped to 43 stimulation channels. A pitch difference limen test was done with normal hearing subjects discriminating pairs of pure tones with different semitone intervals which were processed by a vocoder type simulator of CI sound processing. The results showed better performance with wider semitone intervals. However, no significant difference was found between 22 and 43 channels maps.

Pitch matching in bimodal cochlear implant patients: Effects of frequency, spectral envelope, and level

“…For instance, if the distance between the harmonics were increased, it may be possible to resolve the harmonic structure of complex tones and subsequently pitch perception may be improved. Omran et al (2011) used frequency expansion, and their results showed improved pitch difference limens in NH listeners who were tested with vocoder sounds. Kasturi and Loizou (2007) also showed improvements in melody recognition with such expansion in CI users.…”

Einfluss von Ober- und Untertönen auf die Melodieerkennung mit einem Cochlea-Implantat bei SSD

“…Auch Musiktraining kann sich positiv auf den Musikgenuss auswirken [6,29,30]. Es gibt verschiedene Ansätze, durch verbesserte Filter, Signalcodierung und -verarbeitung das Musikhören zu verbessern [31,32,33,34]. Andere Arbeitsgruppen nutzen die Erkenntnisse über das Musikhören mit dem CI, um maßgeschneiderte Musikkreationen für CI-Träger*innen zu entwickeln [28,35].…”

Interactive Evaluation of a Music Preprocessing Scheme for Cochlear Implants Based on Spectral Complexity Reduction

“…These encompass music rehabilitation and training as described for instance by Galvin et al (2009), Looi et al (2012), and Fuller et al (2018) as well as novel music compositions (Innes-Brown et al, 2012, Nogueira and Herrera, 2015). Also novel implantation techniques (Hochmair et al, 2015), improved signal coding (Omran et al, 2011; Müller et al, 2012; Todd et al, 2017) and signal preprocessing methods have been proposed.…”