Fourier beginner: sanity check
Fourier beginner: sanity check
- Subject: Fourier beginner: sanity check
- From: Phillip Mills <email@hidden>
- Date: Fri, 14 Feb 2003 12:27:18 -0500
For the past few days, I've been trying to learn something about
CoreAudio so that I could capture input and do some analysis. I'm now
at a point I aimed for...but I'm not sure where that is exactly. :-)
(I've been using "A Programmer's Guide To Sound" by Tim Kientzle as a
guide.)
1) My program captures input through the microphone and gets 1024
floats at a time.
2) When the entire capture is finished, I process every second sample
to compensate for interleaved data.
3) Running it through the forward transform in 512 sample chunks gets
me a mirrored curve around the midpoint of the X-axis. (Seems to match
what the book says.)
4) For a particular data block, the maximum of the real values shows up
at offset 9 of the transformed data. I take this as meaning a
frequency near (9/512)*44100 has the highest amplitude.
5) That amplitude is reported as 7.3564, but I have no idea what unit
of measure.
6) The minimum amplitude shows up at offset 8 and, in fact, a graph of
the real values looks like hyperbolic curves around something like
x=8.7, y=0.2.
7) The description of the imaginary part of the result as "Accounting
for Phase" has gone over my head completely. (I understand phase as it
applies to comparing x-axis offsets of waves, but I don't get the
relevance to the goal of obtaining prominent frequencies.)
Any suggestions about where my assumptions don't match reality and any
other relevant hints would be much appreciated. The end result that
I'd like to get to is an estimate of notes and durations for simple
musical input.
Thanks in advance.
_______________________________________________
coreaudio-api mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/coreaudio-api
Do not post admin requests to the list. They will be ignored.