How to decide what platform is best to implement real-time audio processing on?
If you are keeping to "standard algorithms" like IIR, FIR, radix-2 or 4 FFT (ie stuff that fits DSP architectures well without much control flow), you can try this:

Count up how many "multiply accumulates" you need per second in all your algorithms.  


&lt; 10 million you can probably get a fast microcontroller to do the job (or even a slow one if you are &lt;1M)
&lt; 100M is easy DSP territory
&lt; 1G is likely to be doable fast DSP territory
1G-10G is where the cross-over between DSP and FPGA comes
> 10G is multiple DSPs or FPGA