Method and apparatus for efficient multi-stage FIR filters

A signal processing system configured with a digital signal processing filter that alters the sampling rate of a sampled input signal and produces a filtered output signal, comprising:

• a digital signal processing engine;
• a random-access memory configured to store the filtered output signal;
• a cascade arrangement of sub-filters that is executed by the digital signal processing engine and that stores the results in the random-access memory, wherein each sub-filter is configured to provide a sampling rate altering step that produces a filtered signal at a successively higher sampling rate, wherein the sub-filter that generates the filtered output signal is executed first, using data from a previous sampling interval;
• digital output logic configured to output the filtered output signal;
• a digital-to-analog converter to convert the filtered output signal to an analog form;
• an amplifier to amplify the signal converted to analog form;
• and
• a transducer to convert the amplified signal to a sensible form.

A method of altering the sampling rate of a sampled input signal to produce a filtered output signal comprising:

• configuring a random-access memory to store the filtered output signal;
• operating a cascade arrangement of sub-filters with a digital signal processing engine, using each sub-filter to provide a sampling rate altering step that produces a filtered signal at a successively higher sampling rate, running the sub-filter that generates the filtered output signal first using data from a previous sampling interval, and storing the results in the random-access memory;
• and
• operating digital output logic to output the filtered output signal.