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Subject: implementing an fft (fast fourier transform)
From: Jaremy (jaremy_at_uwyo.edu)
Date: 2003-04-24


I am currently developing a fast fourier transform (fft) for rockbox.
For those who do not know what a fft does, it transforms data about the
amplitude into information about the frequency spectrum.

There are several methods for finding the power spectrum, but I am not
sure what units the amplitude data is in. Specifically in the file
oscillograph.c two calls are made:
left = mas_codec_readreg(0xC);
right = mas_codec_readreg(0xD);
Sorry if this is documented somewhere, but could anyone tell me more
information about these calls such as the range, units, etc..? Would
this be the best call to make; it seems the peak analyzer uses a
different call. Also, if they are used in a loop, will the values be at
different times or does the value wait for a tick or any other timing?

If anyone could give me any insight into this, it would be really
helpful in programming the fft, especially on any graphics routines.

Thanks for any information, or any points to the proper documentation.

-- 
Jaremy <jaremy_at_uwyo.edu>



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