Implementation of adaptive digital ANR in hearing protectors

Abstract

Present state-of-the-art personal hearing protectors with ANR are mainly based on analog control circuitry. The performance of these systems is fair to good; an additional attenuation for low frequencies of 10–25 dB is obtained. By using a digital control circuitry for feedback gain control and compensatory filtering, a similar performance can be obtained. Digital signal processing allows for real-time control of the system parameters. By using an adaptive algorithm, the system performance can be optimized for individual (acoustic) frequency transfer and for the spectrum of the specific noise to be suppressed. A prototype system has been developed, in which the feedback gain and the frequency response parameters are adaptively controlled. The system uses an (additional) probe to determine the stability of the feedback loop. Other features of digital ANR are: continuous monitoring of the noise dose, transparency at low noise levels in order to improve direct communications and warning signals, and advanced signal processing of speech signals from an intercom. Preliminary results obtained with an add-on system (attached to a standard earmuff) will be presented and compared to the performance of 20 commercially available systems.