CH12 DSP System Design, Cochlear

CH12 DSP System Design, Cochlear - CHAPTER 12 DSP System...

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C H A P T E R 12 DSP System Design: Cochlear Implant Simulator This chapter covers the real-time implementation of a cochlear implant signal processing simulator by using the LabVIEW hybrid programming approach. A cochlear implant is a prosthetic device surgically implanted into the inner ear that is used to restore partial hearing in profoundly deaf people or patients suffering from nerve deafness. In this device, sounds acquired from a microphone are converted into electrical signals, which are then transmitted to a number of implanted electrodes in the cochlea via radio waves leading to hearing perception [ 1 ]. This chapter covers the signal processing components of a cochlear implant system and their implementations in a hybrid mode. 12.1 Cochlear Implant System A cochlear implant system consists of the following four major components: (1) a microphone that picks up an input speech signal, (2) a signal processor that converts this signal into electrical signals, (3) a transmission system that transmits the electrical signals to implanted electrodes in the cochlea, and (4) an array of electrodes that are surgically inserted into the cochlea. Via the array of electrodes, auditory nerve fibers at different locations in the cochlea get stimulated depending on the signal frequency. A signal processor is used for bandpass filtering the input speech signal into several (12–22) frequency bands. The processor converts the signals from each band into electrical signals and delivers them to the array of electrodes. For a detailed description of cochlear implants, see [ 1 ]. Different signal processing strategies have been presented in the literature for con- verting acoustic signals to electrical signals [ 1 ], [ 2 ]. Here, a vocoder-based strategy known as Continuous Interleaved Sampling (CIS) [ 2 ] is considered. This vocoder 303
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strategy is widely used in commercial cochlear implants. In order to conduct a qualitative analysis of electrical stimuli obtained via the vocoder strategy, a synthesis stage is included along with the decomposition stage in our implementation, as illustrated in Figure 12-1 . The synthesis method implemented here is based on the noise-band vocoder simulation reported in [ 2 ]. As shown in Figure 12-1 , during the decomposition stage, an input speech signal is first pre-emphasized and passed through a bank of bandpass filters. The cut-off frequencies for the bandpass filters are obtained by logarithmically dividing the speech signal bandwidth equally over a given number of channels. The envelopes of the filtered signals are then extracted via full-wave rectification and lowpass filtering with a typical cut-off frequency of 400 Hz. During the synthesis stage, the envelopes obtained after the decomposition are excited with white noise and then filtered through the same bank of bandpass filters that are used during the decomposition stage. Finally, a synthesized signal is reconstructed by summing all the filtered signals as indicated in Figure 12-1 . In essence, the CIS strategy consists of
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  • Fall '16
  • Chen-wei shin
  • Digital Signal Processing, Band-pass filter, Low-pass filter, Cochlear Implant Simulator, Cochlear Implant Simulator System

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