Hello,
where can I find more docs about developing a small spectrum analyzer
and / or an equalizer? I did not speak about source code (I am reading
xmms's), but a good tutorial/paper/book.
Thanks,
tano

I think you'd have to look for FFT (Fast Fourier Transform) algorithms. And there is plenty of docs on that subject.

jlinkels

I also suggest to learn DSP basics and in the context the difference between IIR and FIR filters WRT phase distortions.

Narrow band IIR equalizer can have quite significant phase/group delay distortions which are definitely audible.

Yes, I am reading about fft and in particular I am searching for an understable description
of the sorenson algorithm for real data. But I would like to know thing in a more organic
way.

I don't know what you mean by more organic. The FFT will translate from a function in one domain to a function in another domain - in this case you have a sample with a constant difference in time and the FFT converts to a series with a constant difference in frequency, which is your 'spectrum'. The result of the FFT will also be a complex function so you may want to display the magnitude in your spectrum display (unless you really are interested in seeing the phase information). Do you want to attempt a real-time display or are you happy to play with small samples at a time? Even an ancient 160MHz machine can do the computations fast enough - but if you want to display things real-time then the spectrum analyzer is probably best implemented as a "multi-tap" filter rather than an FFT. Equalizers are best implemented as a digital filter as well rather than two sets of FFTs to implement a filter - in fact, that's how all modern DSP-based equalizers do their job.

Ok, for 'organic way' I intend all the informations correlated to this subject.
What I did is look inside xmms sources and know that it use fft (I read a little on
fft in dspguide, but only as a lecture). The spectrum analyzer is built from magnitude,
even if inside the code the output is not square rooted.
But I did not know if all the samples are sent to the fft function (I have some doubts because the refresh of the spectrum analyzer is configurable, as peak falloff, and more.., so I would like to found a more specific paper about this).
I look also about the equalizer and know that it use "direct form II filter".
I am absolutely new to these kind of things, so what I have to do is *study*.
What you intend for real-time or small samples? The application should display the spectrum in real time
on the screen, yes, but I am not sure this is what you ask me..
However thanks for the ideas, I am searching about multi-tap filters and more..
tano

Don't jump on multi-tap filters yet, start from

http://ccrma-www.stanford.edu/~jos/ ->
http://ccrma-www.stanford.edu/~jos/pubs.html ->
http://www.dsprelated.com/dspbooks/ ->
http://www.dsprelated.com/dspbooks/pasp/
http://www.dsprelated.com/dspbooks/sasp/
http://www.dsprelated.com/dspbooks/mdft/mdft.html
http://www.dsprelated.com/dspbooks/filters/filters.html
.

The second set of examples here are a little fun if I remember correctly:

http://www.speech.kth.se/snack/examples.html

Might help test as you go along...

Thanks!! More news as soon as possible