Combining Directional Microphone and Single-Channel Noise Reduction Algorithms

In Brief Objectives: This study tested a combination of algorithms designed to improve cochlear implant performance in noise. A noise reduction (NR) algorithm, based on signal to noise ratio estimation was evaluated in combination with several directional microphone algorithms available in the CochlearTM CP810 sound processor. Design: Fourteen adult unilateral cochlear implant users participated in the study. Evaluation was conducted using word recognition in quiet, sentence recognition in noise, and subjective feedback via questionnaire after a period of take-home use. Music appreciation was also evaluated in a controlled listening task. The sentence recognition task measured speech reception threshold for 50% morphemes correct. The interfering maskers were speech-weighted noise and competing talkers, which were spatially separated from the target speech. In addition, the locations of the noise maskers changed during the test in an effort to replicate relevant real-world listening conditions. SmartSoundTM directionality settings Standard, Zoom, and BeamTM (used in the SmartSound programs Everyday, Noise, and Focus, respectively) were all evaluated with and without NR. Results: Microphone directionality demonstrated a consistent benefit in sentence recognition in all noise conditions tested. The group average speech reception threshold benefit over the Standard setting was 3.7 dB for Zoom and 5.3 dB for Beam. Addition of the NR algorithm further improved sentence recognition by 1.3 dB when the noise maskers were speech-weighted noise. There was an overall group preference for the NR algorithm in noisy environments. Group mean word recognition in quiet, preference in quiet conditions, and music appreciation were all unaffected by the NR algorithm. Conclusions: Multimicrophone directionality was effective in improving speech understanding in spatially separated noisy conditions. The single-channel NR algorithm further enhanced speech intelligibility in speech-weighted noise for cochlear implant users while maintaining equivalent performance in quiet situations and when listening to music. Noisy conditions pose difficulties for cochlear implant recipients, restricting their ability to understand speech. This study presents the find-ings of a clinical evaluation of noise mitigation algorithms including directional microphones and single channel noise reduction. Fourteen co-chlear implant recipients participated in the study by evaluating the algorithms in a wearable behind-the-ear speech processor. Speech intel-ligibility tests were performed in three difficult listening conditions where the noise was spatially separated from the target speech and also changed location during the test. The findings demonstrate the benefits of combining directional microphones and single channel noise re-duction for daily use in cochlear implants.