Re: One more little question

"anthony" <ajh@xxxxxxxxxxx> wrote in message
news:4lUNe.4310$iM2.444556@xxxxxxxxxxxxxxxxxx

> How does one change the key of a mp3 or wave file. There are lots of
> programs around that will do it on the fly. I have to use a third party
> product to actually change the whole file permently. But there are as
> I say of other software that will do the chang on the fly without
> actually changing the file.

Changing the key is done by multiplying all the tone frequencies present
in the music by a constant factor. Multiply by two for one octave higher,
by .5 for one octave lower, etcetera. This is easy when you have the data
as a function that tells you the amplitude for each frequency (just shift
the whole function left or right by a fixed offset) and totally impossible
when you have it as 44.1K samples per second. Fortunately, you can convert
between the two with Fourier's transform. Google for FFT and please read
MathWorld for two days before coming back here to ask how the hell it
works.

Wav files must, as hinted at above, be converted to the frequency domain,
shifted, and transformed back. Mp3 files are encoded in frequencies
already, so they only have to be shifted and transformed back. There,
the problem is that the encoded data need to be uncompressed first.

Groetjes,
Maarten Wiltink


.

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