Re: One more little question

Thank you very much for that, all I wanted was how it is done, I dont want
to implement that feature, but I am please that someone knows how it done.
Once again that you


"Maarten Wiltink" <maarten@xxxxxxxxxxxxxxxxxx> wrote in message
news:43097b20$0$11078$e4fe514c@xxxxxxxxxxxxxxxxx
> "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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