title: Investigating the use of a Gammatone filterbank for a cochlear implant coding strategy.
abstract: Contemporary speech processing strategies in cochlear implants (CIs) such as the Advanced Combination Encoder (ACE) use a standard Fast Fourier Transform (FFT) filterbank to extract envelopes. The assignment of the FFT bins to approximate the frequency resolution of the basilar membrane is only partly based on physiology, especially since the bins are distributed linearly below 1000Hz and logarithmically above 1000Hz.
  
  
  
  A Gammatone filterbank which provides a closer approximation to the bandwidths of filters in the human auditory system could replace the standard FFT filterbank in the ACE strategy. An infinite impulse response (IIR) all-pole design of the Gammatone filterbank was compared to the FFT filterbank with 128, 256 and 512 points resolutions and the effect of the frequency boundaries of the filters was also investigated.
  
  
  
  Melodic contour identification (MCI) and just noticeable difference (JND) experiments, both involving synthetic clarinet notes in octaves 3 and 4, were conducted with 6 normal hearing (NH) participants using noise vocoded stimuli; and 10 CI recipients just performed the MCI experiment. The MCI results for both NH and CI subjects, showed a significant effect of the filterbank on the percentage correct responses of the participants.
  
  
  
  The Gammatone filterbank can better resolve the harmonics of tested synthetic clarinet notes which led to better performances in the MCI experiment.
  
  
  
  The total delay of the Gammatone filterbank can be made smaller than the delay of the FFT filterbank with the same frequency resolution at low frequencies.
authors.affiliation: Department of Information Technology and Electrical Engineering, ETH Zürich (ETHZ), Zürich, Switzerland; Laboratory of Experimental Audiology, ENT Department, University Hospital Zürich, Zürich, Switzerland. Electronic address: sonia.tabibi@usz.ch.
authors.forename: Sonia
authors.initials: S
authors.lastname: Tabibi
authors.affiliation: Laboratory of Experimental Audiology, ENT Department, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kegel
authors.affiliation: Laboratory of Experimental Audiology, ENT Department, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Wai Kong
authors.initials: WK
authors.lastname: Lai
authors.affiliation: Laboratory of Experimental Audiology, ENT Department, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Norbert
authors.initials: N
authors.lastname: Dillier
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000704:Analysis of Variance; D001307:Auditory Perception / Q000502:physiology*; D001931:Brain Mapping; D003054:Cochlear Implants; D004558:Electric Stimulation; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D005583:Fourier Analysis; D006311:Hearing Disorders / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D009146:Music; D010898:Pitch Perception
keywords: ACE strategy; Cochlear implant; Gammatone filterbank; Just noticeable difference; Melody contour identification