Speech Understanding Performance of Cochlear Implant Subjects Using Time–Frequency Masking-Based Noise Reduction

Abstract

Cochlear implant (CI) recipients report severe degradation of speech understanding under noisy conditions. Most CI recipients typically can require about 10-25 dB higher signal-to-noise ratio than normal hearing (NH) listeners in order to achieve similar speech understanding performance. In recent years, significant emphasis has been put on binaural algorithms, which not only make use of the head shadow effect, but also have two or more microphone signals at their disposal to generate binaural inputs. Most of the CI recipients today are unilaterally implanted but they can still benefit from the binaural processing utilizing a contralateral microphone. The phase error filtering (PEF) algorithm tries to minimize the phase error variance utilizing a time-frequency mask for noise reduction. Potential improvement in speech intelligibility offered by the algorithm is evaluated with four different kinds of mask functions. The study reveals that the PEF algorithm which uses a contralateral microphone but unilateral presentation provides considerable improvement in intelligibility for both NH and CI subjects. Further, preference rating test suggests that CI subjects can tolerate higher levels of distortions than NH subjects, and therefore, more aggressive noise reduction for CI recipients is possible.

Sparse Nonnegative Matrix Factorization Strategy for Cochlear Implants

“…Since NCM gives a larger optimal λ at SNR=0 than STOI, it indicates that the algorithm is more sparse or “aggressive” in lower SNR conditions. A previous study (ur Rehman Qazi, van Dijk, Moonen, & Wouters, 2012) showed that CI subjects generally tolerate higher levels of distortion than NH subjects, and therefore, more aggressive noise reduction may be appropriate for CI recipients. To set more varied sparsity levels for CI subjects, NCM was used to initialize the λ values in Experiment III.…”

Comparing Binaural Pre-processing Strategies II

“…For the perceptual evaluation with bilaterally implanted CI users, different parameter settings of the SCNR algorithm were chosen than were used in the instrumental evaluation ( Baumgärtel et al., 2015 ). It has previously been shown ( Qazi, van Dijk, Moonen, & Wouters, 2012 ) that CI users are able to tolerate more signal distortion introduced by noise reduction algorithms compared to NH or HI listeners. Therefore, a more aggressive parameter set was chosen for the bilateral CI evaluation compared to the default setting.…”

ForwardFocus with cochlear implant recipients in spatially separated and fluctuating competing signals – introduction of a reference metric

“…A system using a moderately directional microphone on each ear (Audallion BEAMformer) was shown to provide similar benefit to a unilateral moderately directional microphone (Spriet et al 2007). With two sound processors connected with a bi-directional wireless link, bilaterally implemented directional microphones (B€ uchner et al 2014) or bilateral masking-based technologies (Qazi et al 2012) have shown moderate improvements compared to unilateral adaptive beamforming. However, these systems require two sound processors to be worn, and impact battery life due to the power requirements of the wireless link.…”