This Figure shows the polyphase decimation filter option which implements the computationally efficient M -to-1 polyphase decimating filter.
A set of N prototype filter coefficients is mapped to the M polyphase subfilters according to Equation 3-1 .
The polyphase segments are accessed by delivering the input samples x ( n ) to their inputs using an input commutator which starts at the segment index and decrements to index 0. After the commutator has executed one cycle and delivered M input samples to the filter, a single output is taken as the summation of the outputs from the polyphase segments. The output sample rate is where is the sample rate of the input data stream .
Observe that each of the polyphase segments is operating at the low output sample rate (compared to the high input sample rate ), and a total of operations is performed per output point.