Hybrid finite impulse response filter

A method comprising:

• filtering with a high-rate filter portion of a hybrid finite impulse response filter having a plurality of delay stages and an input signal having a first sampling rate to generate a first intermediate output signal;
• downsampling the input signal to a downsampled input signal having a second sampling rate smaller than the first sampling rate;
• filtering with a low-rate filter portion the downsampled input signal;
• upsampling the downsampled input signal as filtered by the low-rate filter portion to generate a second intermediate output signal having a sampling rate larger than the second sampling rate;
• and
• summing the first intermediate output signal and the second intermediate output signal to generate an output signal of the hybrid impulse response filter.

An integrated circuit for implementing at least a portion of a personal audio device, comprising:

• an output for providing an output signal to a transducer including both a source audio signal for playback to a listener and an anti-noise signal for countering the effect of ambient audio sounds in an acoustic output of the transducer;
• a microphone input for receiving a microphone signal;
• and
• a processing circuit that implements:
• a hybrid filter that generates the anti-noise signal to reduce the presence of the ambient audio sounds at the acoustic output of the transducer based at least on the microphone signal, the hybrid filter comprising:
• a high-rate filter portion configured to filter an input signal having a first sampling rate to generate a first intermediate anti-noise signal;
• a low-rate filter portion configured to filter the input signal downsampled to a second sampling rate to generate a second intermediate anti-noise signal;
• and
• a summer to sum the intermediate anti-noise signal and the second intermediate anti-noise signal to generate the anti-noise signal.

A hybrid finite impulse response filter having a plurality of delay stages, comprising:

• an analog filter portion associated with a first portion of the plurality of delay stages and configured to filter an input signal to generate a first intermediate output signal;
• a digital filter portion associated with a second portion of the plurality of delay stages and configured to filter the input signal to generate a second intermediate output signal;
• and
• a summer for summing the first intermediate output signal and the second intermediate output signal to generate an output signal of the hybrid impulse response filter.

A method comprising:

• filtering with an analog filter portion associated with a first portion of a plurality of delay stages of a hybrid finite impulse response filter an input signal to generate a first intermediate output signal;
• filtering with a digital filter portion associated with a second portion of the plurality of delay stages the input signal to generate a second intermediate output signal;
• and
• summing the first intermediate output signal and the second intermediate output signal to generate an output signal of the hybrid impulse response filter.