LabVIEW and digital signal processor implementation of a channel vocoder based model of a cochlear implant

Abstract

A cochlear implant is a prosthetic device used to mimic the function of a cochlea in a person with profound and bilateral hearing loss caused by a damaged inner ear. The current work revolves around the design of real time channel vocoder based model of a cochlear implant in LabVIEW and the TMS320C6713 DSK. First, a uniform band 16-channel vocoder is designed for the analysis and synthesis of English vowels, where filters of 400 Hz bandwidth, with cut off frequencies up to 6200Hz are used, based on MATLAB analysis performed previously. To extend the analysis to words and sentences, short time features, namely, short time energy, short time zero crossing rate and main lobe width of the short time autocorrelation function, are extracted and Gaussian Mixture Modelling (GMM) is used to classify the speech segments as voiced or unvoiced. In an attempt to make the synthetic speech sound natural, the synthesis in the channel vocoder is done using a train of glottal pulses instead of a train of impulses. The intelligibility of the synthetic speech is measured by the Mean Opinion Score (MOS). For a channel vocoder where the synthesis section uses a train of glottal pulses, an MOS of 3.6 is obtained as against 3.5 when a train of impulses is used. The lab model of the cochlear implant, that is, the analysis section of the 16-channel vocoder is then realised in the TMS320C6713 DSK. Individual channel outputs are obtained by programming the DIP switches of the DSK and a DSK_AUDIO16_BASE, a 16-channel audio daughter card, is interfaced with the DSK to obtain the outputs from multiple channels simultaneously.