fft on nios

Sorry I don't have any examples of wiring up the FFT core to an SOPC Builder system but it should be fairly straight forward to do using component editor in SOPC Builder. You might need to include some wrapper logic around the FFT core.

Do you need to perform the FFT at high speeds or can you use a software based FFT? If you need to use hardware I would expect the following data flow:

Codec --> DMA --> FFT --> DMA --> Memory

Using a pair of DMAs would be easiest but you could get away with using a single DMA assuming there is enough buffering present in the FFT to support this.