Delayless polyphase implementation of filters in active noise control systems

Abstract

In real-time implementation of active noise control filters, high sampling rate is sometimes preferred to reduce the delay in analog-to-digital converters or to reduce the risk of aliasing effect. A multi-rate structure is usually implemented with a polyphase structure to maintain a low sampling rate for the control filters to avoid the increase of real-time computational load. However, the use of decimation or interpolation filter will introduce additional delay, which can negatively affect the noise control performance. In the current work, a delayless implementation of polyphase structure is proposed where the original active noise control filter is first constrained to have sufficient attenuation at high frequencies in its design phase and is then decomposed into two multiplicative sub-filters, each of which involves a sufficiently high frequency attenuation. These two decomposed sub-filters can perform both noise control and decimation/interpolation without introducing additional delay in the polyphase structure. The proposed delayless approach can thus reduce the delay of a traditional multi-rate active noise control system and, in principle, can provide better active noise control performance. Moreover, if a single rate system is implemented at a high sampling rate, the proposed polyphase structure in filter implementation can effectively reduce the real-time computational load.