Audio signal echo reduction

A system for reducing echo in an audio signal, comprising:

• (a) a plurality of inputs for inputting:
• an input signal, an estimate of a system-characterizing function, and a reference signal, each at a corresponding sample rate and each divided into a plurality of sub-bands;
• (b) a plurality of echo-cancellation modules, each said echo-cancellation module including:
• (i) an echo-estimation module that inputs the estimate of the system-characterizing function at a first sample rate and the reference signal at a second sample rate and that, processing at a third sample rate, outputs an echo estimate signal at a fourth sample rate, and (ii) a subtractor that subtracts the echo estimate signal from the input signal, also at the fourth sample rate, to produce an echo-canceled sub-band signal at the fourth sample rate;
• and
• (c) a synthesis module that synthesizes the echo-canceled sub-band signals from said echo-cancellation modules to produce a final output signal,
• wherein the third sample rate is lower than the fourth sample rate, and
• wherein when processed to generate the echo estimate signal within at least one of echo-cancellation modules, the system-characterizing function and the reference signal have different sample rates.