Signal Processing has been used for many years to realize enhanced performance and reduced cost of the ADC and DAC processes. The Sigma-Delta converter is a well-known example of the application of DSP to realize enhanced performance conversion. The sigma delta converter can be used as an A/D, as a D/A, as a D/D as well as a signal conditioner for other processing tasks. The signal processing which accompanies the sigma delta modulator performs a multi-rate filtering task, which entails a bandwidth reduction and a sample rate change.