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From this descriptin I think this will be an audio applications. In this case I suggest ou to take audio codec which you can interface through SPI and have all audio filters built inside - otherwise you will need quite powerfull CPU to realize this filters.
In my application I use 16 bit TI DSP TMS320LF2407(a) (30(40) mips) and TLV320C1106 or you can use TLV320AC36 which costs app. 3USD. This audio codec can be interface on any platform which have SPI on minimum 2MHz - This is standard surce clock for most of Codecs.
The AK5371 is a low-power, stereo input ADC with a built in USB interface. This device is perfect for USB microphones, microphone arrays, and USB audio capture and headset applications. If a USB codec is required, check out AKM's AK4571.