AudioBanter.com - View Single Post - Fourier Analyses, or, how the Orchestra learned to play "Jet Engine"

(Scott Dorsey) wrote in message
I'm listening to Toots and the Maytals as I type this...

Woah. New stuff? I haven't even heard the title before. I'm kinda
weening off the Youth a little bit. Nowadays I'm really into Ligeti.
Have you heard his "Atmospheres" or his "San Fransisco Polyphony", or
his "Continuum (fur Cembalo)"? My goodness! They're must-listens.
He has some of the most revolutionary music I have ever heard. I'm
sure you will understand my wanting for a type of software like this
once you hear these pieces, if you haven't heard them already.

So what I have to do is perform FFT on each of my sound "samples", the
squeak of a vilon played behind the bridge, a viol's "dry string"
sounds, regular arco, pizzicato, etc, ect, all the ohter instruments,
etc. And then perform an FFT on any given sound file I'm interested
in emulating. After that, what kind of math would be used to sort
through all the samples and figure what goes best where?

I'm not sure this will really do what you want, but you can try it. You
could just do a standard correlation coefficient and see how close they
come.

Then again, you could probably just do a correlation coefficient on the
samples themselves. That might be fun to look at.

A correlation for the whole sound file, or a correlation every set
number of seconds, or a type of gui tool to use to set up the sections
you want to emulate. This would be good for Monophonic reduction, but
more math would be involved if you wanted to reduce the sound file to,
say, 3 concurrent, or 13 concurrent instruments, right?

Ideally this software would/could use both of these approaches.

Samplitude features an FFT analyses window. It just looks like a
regular EQ anlysis to me. Is it the case that if I take each
frequency as a sine wave and apply it to the given amplitude that I
will have achieved X's sound? Is there anyway to simplify that? Even
the simplest natural sounds have about a 5khz range. Do I have to
create 5000 individual sine waves? The FFT graph only shows frequency
over time, How do I find out about the relationships between the
frequencies as far as timming? For example say a put a sine wave at
2Khz and 1Khz. Obviously the 2Khz occilates twice as fast as the 1
Khz, but beyond that, the starting/ending points (where y=0) might not
sink up. The 2Khz sine may start, say, 300ths of a second after the
1Khz. I don't think info like this can be found out by the FFT
window, can it?

No, you probably want a tool like matlab. How many terms you want to
calculate out to depends on how good an approximation you want. I think
that the number of terms that you're going to get is going to be larger
than the number of samples in the original file for most arbitrary sounds.
You can decide to reduce this by bandlimiting the original signal, though.
--scott

Terms? As in how many instruments I want to end up with? Or by what
specs I will measure the orignal soundfile? If the later, do you mean
something like bitrate, samplerate, something else? Why would the
number of terms be greater than the samplerate? Is matlab an audio
tool. Probably just a math program right? So I would enter in pcm
info and run the calculations and then use the output to create a pcm
file? Sorry so many questions.