Take a look at Cypress PSOC, 5LP family. It is a GP processor with a
separate DSP engine in it for filtering work. People have also implemented
FFT on it.
Your sampling rate and precision might be a challenge in PSOC, depends
on what you want to do to the digitized signal. The SAR, 12 bits, can do 1
Mhz, the DelSig can do 16 bits at 48 Ksps. The DSP engine is DMA driven,
so can handle basic filtering in background due to buss architecture and
spoke engine.
www.cypress,com, PSOC 5 family, ,many
videos for training, etc..
Attached an example project, one of many, that are available in IDE
for examination, use. Note PSOC has I2S module that can be used for
audio work.
Regards, Dana.