Adaptive Noise Cancelling in Headsets - Preliminary Simulations and Realisation

In classical analogue noise cancelling the intruding soundfield is recorded, phase inverted, and remitted through headphones. At its maximum the attenuation is app. 20dB and in the frequency range below app. 1kHz only. Digital noise cancelling seems to offer better attenuation, exceeding 25dB in a larger frequency range. The present work describes the LMS and NLMS adaptive filtering techniques. Simulation results based on white and pink noise excitations as well as the attempt to use a standard fixed-point Analog Device DSP development board to implement the noise canceller. The inherent delay of the built-in sigma/- delta converters, however, deranges the adaptive algorithm, hence excluding the present application on the particular hardware. 1. INTRODUCTION Noise reduction systems in headsets represent a successful application of active noise cancellation. Up to now the major part of practical implementations is based on analogue feedback principles. Bose [1] and Sennheiser, among oth..