POLAR PLOTS OF A DIRECTIONAL MICROPHONE WITH REAL-WORLD SOUNDS AND ITS SPECTRUM DISTORTION

Abstract

Some references discussed and evaluated performances of conventional directional microphones in hearing aids, from their conclusions, it is undoubted for the microphones to improve S/N, yet conditions of the advantage somewhat confused to hearing aid clinicians and professionals. To supplement the incompletion, we investigated behaviors of a directional microphone in extensive situations. We built an SimuLink laboratory, selected realistic talking voices and noises from wave files and made many experiments to find out illustrative evidences. Electroacoustic models are used for components of modelling a directional microphone; we operated the microphone with these sounds from real-world to calculate, view, measure and record behaviors of the directional microphone. We acquired  many waveforms, statistics and recordings of the experiments with woman’s and man’s talking voices, and environmental noises; we also listened to sounds at input and output of the directional microphone to perceive changes of the speech naturalness. Comparing to an omni microphone, the directional microphone does not enhances the speech signals on average; sensitivity-gain of the directional microphone is higher than that of the omni microphone when the tone frequency > 1.78 kHz; the directional microphone cancels the undesired speech well, as well as the babble noise and the environmental white noise from a beamed source at rear side; the directional microphone cannot improve the S/N of a speech within babble or white noise fields; in addition, we also observed and heard the speech spectrum distortion caused by the directional microphone