Abstract:

A digital, adaptive ANR headset system has been developed and tested in the laboratory, using a filtered-X LMS adaptive control algorithm and a floating-point digital signal processor (DSP). The implementation of the filtered-X LMS adaptation algorithm requires an impulse response (IR) model of the so-called ``error-path,'' which consists of the serial connection of an earphone, earcup acoustics, microphone, and electronic amplifiers and filters. Though the IR model can be measured off-line for laboratory studies using standard measurement procedure, on-line measurement or identification, using the DSP engine and digital signal processing techniques, is considered necessary and advantageous for practical applications. This paper discusses a DSP-based identification technique for the error-path IR model, which employs the well-known pseudorandom binary signal (PRBS), also called the maximum length sequence (MLS) signal, as the input to the error path. In this paper, the measurement method and system will be discussed. As an example, the error-path impulse response and the corresponding ANR results obtained in a laboratory setup will be presented. [Work supported by DCIEM, Toronto, Canada.]