Digital filter arrangement for ambient noise reduction, using an oversampled audio signal

摘要

A digital circuit arrangement for an ambient noise-reduction system uses a low latency signal processing chain. The circuit arrangement includes a digital filter 82, which preferably comprises an IIR filter and delta-sigma modulator, for generating a digital noise cancellation signal which is received by a 1-bit digital-analogue converter. The arrangement preferably converts analogue ambient noise signals, collected by microphone 13, into digital signals and then subjects the converted signals to digital filtering. The digital signals are N-bit digital signals at sample rate f0, where the value of N is no greater than 8, and fo is at least 8 times the Nyquist sampling rate required for sampling of audio signals. This permits digital processing to be used without incurring group delay problems that rule out the use of conventional digital processing in this context. This arrangement is suited to devices incorporating a loudspeaker in proximity to the ear, such as headphones and telephone handsets.