- PRE-SHAPING SERIES FILTER FOR ACTIVE NOISE CANCELLATION ADAPTIVE FILTER

摘要

A feedforward active noise canceling (ANC) system for use in portable audio devices has an adaptive digital filter and a reference microphone. A non-adaptive pre-shaping digital filter has an input connected to a reference microphone, which is in series with the adaptive filter in front of it. The pre-shaping filter is minimal phase and exhibits more gain by more than 2 dB over the lower audio frequency band for the higher audio frequency band. This can help compensate for low frequency band difficulties, thereby extending the ANC bandwidth in the low end without adversely affecting the high end. Other embodiments are also described and claimed.