Multirate filtering is used to change the rate or frequency of sampling of an input signal to an arbitrary rate or frequency at the output. Multirate filtering is widely used in video applications. DSP58 is ideally suited to implement multirate sampling because of its high speed and filter-like structure. The cascaded data input and output paths, pipeline registers, high precision two’s complement multiplier followed by an adder/subtracter, and accumulation capability provide needed elements for multirate filtering.
Polyphase interpolating and decimating FIR filters are used to implement multirate filters using up-sampling and down-sampling techniques. They are covered in the following sections.