Help understanding FFT and/or DSP

[Sismetic]

Hi, Im trying to do a screen-flashing application, that flashes the screen according to the music(which will be frequencies, such as healing frequencies, etc...). I already made the player and know how will I make the screen flash, but I need to make the screen flash super fast according to the music, for example if the music speeds up, the screen-flash will flash faster. I understand that I would achieve this by FFT or DSP(as I only need to know when the frequency raises from some Hz, lets say 20 to change the color, making the screen-flash).

But I've found that I understand NOTHING, even less try to implement it to my application.

Can somebody help me out to learn whichever both of them? My email is [e-mail]. I really need help, I've been stucked for like 3 days not coding or doing anything at all, trying to understand, but I dont.

PS:My application is written in C++ and Qt.

PS:Thanks for taking the time to read this and the willingness to help.

[Software guy]

Hi,
I have studied DSP and FFT in detail. But I am afraid it cannot help you in programming. FFT is further derivation of Fourier series. Because the problem with fourier series is that you cannot use it for aperiodic signals. But FFT can be used for aperiodic signals, because we assume that time period is infinite, while in fourier series we dont have this assumption.

Whatever I wrote might not make sense, but FFT can give you the DFT of each sample in audio. But I still cannot link this concept with your problem. I think I need more detail about the task your working on.

[gsfare]

Check out the GNU scientific library here http://www.gnu.org/software/gsl/. The library will perform the FFT for you. This will transform your signal from the time domain into the frequency domain. After that you need to calculate the entropy of the signal, or how much power is associated to each frequency in the signal. That will give you a spectrum entropy signal which is what you're after I think. Sounds complex but there's LOADS of material on the web describing how to do it.

I prefer wavelets...but that's another story.

[Software guy]

I would also advise you to use MATLAB, before finalising any results. MATLAB is very easy to use and has built in functions to do High level of signal processing and it can plot the graphs for you.

[Sismetic]

@software guy: Maybe you could message me and I could explain in more detail, even show the code, because I dont seem to be able to explain myself properly(no one ever understands what I say :P), in my defense english is not my native language.

@gsfare: Im checking the library, but my problem is not getting libraries(FFTW is a good one), the problem is I don't understand how to apply it to my problem, I don't understand what the examples I see sometimes are supposed to do or return or whatever. I'm the problem :P, Im stupid and can't understand it. Do you know a tutorial for dummies(real dummies) of FFTP and it's application in C++ or DSP?

To both: Thanks for answering so quickly, and your willingness to help, I really appreciate the answers.