I would like to work on project that is very similar to what the Spectrum Shield can do, but would like to have a larger frequency range than the 7 bands the board can initially provide. I have found and experimented with an FHT (FHT is a Fast Fourier Transform that runs a little faster by ignoring the imaginary numbers) library that takes a signal and parses it into a larger number of bands.
http://wiki.openmusiclabs.com/wiki/ArduinoFHT
Essentially, my goal is to get a signal from an audio jack from a phone or computer - probably a 3.5 mm jack. Then, with this signal, use the library linked to break the signal into an amplitude over a specific frequency range.
Does the Spectrum Shield automatically perform its calculations to break the input signal down automatically? Or is it possible to get the signal that goes into the calculations first, such that the arduino could do its own analysis. I’m assuming the signal is modified so that it can run something like a FFT first, by changing the range from -2.5V to +2.5V, to 0V to +5V. Is this correct?