Active noise reduction for cellular and PCS handsets

Abstract

The effectiveness of active noise reduction (ANR) technology in Prototype cellular and PCS handsets has been investigated by developing prototype terminals with both feedback and feedforward control approaches. In contrast to ANR headsets, which present a relatively stable and favorable earpiece (i.e., receiver-error-microphone) transfer function (TF) to the ANR control system, an even greater challenge is faced in applying ANR to cellular/PCS handsets where the corresponding TF varies with positioning of the earpiece about the ear. As a first step in the investigation, a practical cellular/PCS handset earpiece, suitable for ANR, but with reduced position variability in the earpiece TF, has been developed using a lumped parameter, equivalent circuit model of the earpiece–ear system. Experimental results are presented for the new earpiece design tested against different users’ ears and against several acoustic load impedances. As the next step in the investigation, both feedback and fixed feedforward ANR control algorithms were implemented on a low-latency programmable ASIC developed specifically for ANR applications. The ANR performance results are presented for both feedback and feedforward designs tested against a range of users and also as measured against a B&K 4195 ‘‘leaky’’ coupler.