Post Made Community Wiki by Kevin Vermeer
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In addition to the often suitable general-purpose-processor ideas, there have been some dedicated DSPs marketed which deliver either BiQuad or FIR filters, either built into an ADC/DAC chip, or as a tiny stand alone part with something like I2S in and out.

The idea seems to be that by doing this in special purpose hardware, you can configure it from an embedded CPU, without having to pick one with DSP horsepower or design your embedded software in such a way that near-real-time processing of the data is assured.