Pretty fast..
My audio spectrum analyzer project does 128 analog samples per "read",
performs a FFT on the data, and displays it by generating video in realtime-
a 32-band EQ display- and does all that roughly thirty times a second. There's
no external active hardware.. just the arduino, a microphone/preamp, and
the couple of resistors required to use the TVout lib.
The sampling rate on the Arduino can be stunning.. ten zones:
Video frames for reliable read (typically) seems around 3.. but I'm working
on that. Assume three for now, and that means ten zones, three frames per,
makes thirty video frames per "scan", or a sample rate of half a second at
a worst-case scenario with decent discrimination. That's assuming the worst-
using a TVout Lib implementation on a small LCD. If you are using something
like a LED array, then you control the refresh rate and your lag just becomes
the phototransistor and A/D settle times, which are TINY. Most of the time
my project just is waiting for the TV to update- which for scanning purposes,
is woefully slow at 60hz..
so Yeah, it can do that... 