A fast algorithm for polyphase quadrature filters

A fast algorithm for computing the polyphase quadrature filters (PQF), which are typically used in data reduction of audio and speech signals, enables the implementation of either a larger number of subbands or a better data reduction method, or both, in real-time applications. The algorithm, which was developed for use in a hidden channel approach, has been implemented on a Motorola 56001 (27 MHz), where the fast algorithm enables practical use of more than 32 subbands on audio signals. As the number of calculations for M subbands is reduced from approximately M² to M log₂(M), a 64-band analysis or synthesis filter requires only about 22% of the computation capacity compared with approximately 43470 with other algorithms