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Different results

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Adau

28 Jun, 2010 08:10 PM

Hi,

I analysed a same playlist with the same settings on two different computers and the result was different.
Look at these two screenshots. Some tracks don't have the same key. And colors are differents (So if I want to sort my playlist by color, I don't have the same order)

Can you tell me why ?

Thank you,
Adau.

• Screenshot_001.jpg 47.5 KB
• Screenshot_002.jpg 143 KB

1. Support Staff 1 Posted by hendrik on 29 Jun, 2010 07:19 AM

   

   Hi,

   The color differences are easily explained, as colors are collection specific. I.e. unless you analyzed the same songs (not more and not less) of your whole collection, the colors will be different guaranteed.

   Two technical details can also lead to differences:

   • On OSX beaTunes uses CoreAudio, on Windows it uses QuickTime
   • On OSX beaTunes uses the Fourier transform provided by the Accelerate framework to take advantage of whatever Apple engineers managed to tweak out of the CPU. On Windows a straight forward FFT is used.

   I was able to reproduce the differences with some songs and will try to figure out what the exact source of it is.

   -hendrik

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2. Support Staff 2 Posted by hendrik on 29 Jun, 2010 09:31 AM

   

   Hi,

   I did some digging and apparently QuickTime tends to report different track durations than CoreAudio or even QTKit. This is relevant, because for (e.g.) key detection beaTunes skips the first quarter of a song before it actually analyses any data. That way it can ignore the first couple of meaningless beats that usually come first in a song. Now, if the length is reported differently, it jumps to a different position in the file, which can lead to different results - especially when the algorithm is "torn" between two different keys.

   I've asked Apple how to work around this, but I don't expect a useful answer.

   -hendrik

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