Speech recognition with a hearing-aid processing scheme combining beamforming with mask-informed speech enhancement.

A signal processing approach combining beamforming with mask-informed speech enhancement was assessed by measuring sentence recognition in listeners with mild-to-moderate hearing impairment in adverse listening conditions that simulated the output of behind-the-ear hearing aids in a noisy classroom. Two types of beamforming were compared: binaural, with the two microphones of each aid treated as a single array, and bilateral, where independent left and right beamformers were derived. Binaural beamforming produces a narrower beam, maximising improvement in signal-to-noise ratio (SNR), but eliminates the spatial diversity that is preserved in bilateral beamforming.

Forward Masking in Cochlear Implant Users: Electrophysiological and Psychophysical Data Using Pulse Train Maskers.

Electrical stimulation of auditory nerve fibers using cochlear implants (CI) shows psychophysical forward masking (pFM) up to several hundreds of milliseconds. By contrast, recovery of electrically evoked compound action potentials (eCAPs) from forward masking (eFM) was shown to be more rapid, with time constants no greater than a few milliseconds. These discrepancies suggested two main contributors to pFM: a rapid-recovery process due to refractory properties of the auditory nerve and a slow-recovery process arising from more central structures.

Pulse-spreading harmonic complex as an alternative carrier for vocoder simulations of cochlear implants.

Noise- and sine-carrier vocoders are often used to acoustically simulate the information transmitted by a cochlear implant (CI). However, sine-waves fail to mimic the broad spread of excitation produced by a CI and noise-bands contain intrinsic modulations that are absent in CIs. The present study proposes pulse-spreading harmonic complexes (PSHCs) as an alternative acoustic carrier in vocoders.

Optimizing pulse-spreading harmonic complexes to minimize intrinsic modulations after auditory filtering.

All signals, except sine waves, exhibit intrinsic modulations that affect perceptual masking. Reducing the physical intrinsic modulations of a broadband signal does not necessarily have a perceptual impact: auditory filtering can reintroduce modulations. Broadband signals with low intrinsic modulations after auditory filtering have proved difficult to design.

Effects of noise suppression on intelligibility. II: An attempt to validate physical metrics.

Using the data presented in the accompanying paper [Hilkhuysen et al., J. Acoust.

Effects of noise suppression on intelligibility: experts' opinions and naive normal-hearing listeners' performance.

Purpose: In this study, the authors investigated how well experts can adjust the settings of a commercial noise-reduction system to optimize the intelligibility for naive normal-hearing listeners.

Method: In Experiment 1, 5 experts adjusted parameters for a noise-reduction system while aiming to optimize intelligibility. The stimuli consisted of speech presented in car-cabin noise or babble at 5 different signal-to-noise ratios (SNRs).

Effects of noise suppression on intelligibility: dependency on signal-to-noise ratios.

The effects on speech intelligibility of three different noise reduction algorithms (spectral subtraction, minimal mean squared error spectral estimation, and subspace analysis) were evaluated in two types of noise (car and babble) over a 12 dB range of signal-to-noise ratios (SNRs). Results from these listening experiments showed that most algorithms deteriorated intelligibility scores. Modeling of the results with a logit-shaped psychometric function showed that the degradation in intelligibility scores was largely congruent with a constant shift in SNR, although some additional degradation was observed at two SNRs, suggesting a limited interaction between the effects of noise suppression and SNR.