Well Syd, you're going to be as shocked as I was with how fast the FFT runs.. in my implementation, not only is our little Arduino doing the sampling and FFT's, it's also generating composite video, completely in code, thanks to the TVout library. I'm still doing some tweaking (after which I will do actual timing to see the exact rate), but with the build I wrote up, I'm guessing it's updating (which means a sample/process/display pass) the screen at around 10 times per second. A 10Hz frame rate isn't going to be too good for an analytical device, but for a light show, it'll do just fine. The majority of the time is actually being consumed by the line-drawing routines for the bars, rather than the data transform math... since your code handling output will no doubt be less "weighty" than generating NTSC video, you will probably get a MUCH higher update rate.