A Noise Robust Hearable Device with an Adaptive Noise Canceller and Its DSP Implementation

This paper presents a noise-robust hearable device with an adaptive noise canceller. The hearable device has an inner-ear and an outer-ear microphone to collect ear-canal speech signal and the outer-ear environmental signal, respectively. The environmental signal drives an adaptive filter to generate a noise replica which is subtracted from the inner-ear microphone signal to cancel the noise. Coefficients of the adaptive filter are updated by an NLMS (normalized least mean square) algorithm with an SNR-controlled stepsize for small speech distortion. The adaptive noise canceller is realized on a DSP (digital signal processor) chip with 39 McPS for 64 taps. Evaluation results in speech recognition demonstrates that a word recognition rate of 89% is achieved when the noise level is 80 dBA with 38% improvement over the inner-ear signal without adaptive noise cancellation.