Hopefully I'm in the right section, please ignore/delete if not!

I've noticed that it sometimes, for some albums, or even songs, WMP 12 doesn't even remotely offer the predicted 20.5kHz cutoff reserved for 320kbps mp3 files. Not sure whether it matters, but the file is Iron Maiden from the eponymous 1998 Remaster/Expanded CD.

I'm ripping directly from the CD, which isn't at fault (I ripped a test WMA lossless file and it was OK -- 22kHz cutoff, completely full with green/blue colour).

Here's a a spectral comparison comparison with iTunes rip (same 320CBR): http://i.imgur.com/yukJAol.jpg

As you can see, WMP mostly cuts most of the "blue" data (noise?) --- I've been told that this is possibly a proprietary psycho-acoustic model or an undocumented 16kHz low pass filter. However this is weird since iTunes and WMP use the more or less same codec. (FhG "ACM/Producer Pro" in WMP12 and FhG "fastenc/mp3enc" in iTunes 12. Source: EncSpot)

Here's the spectral comparison of another track, this time Phantom of the Opera -- again not remotely (maybe I'm wrong) 320kbps when you look at it. Especially not the WMP version. http://i.imgur.com/SrD7JIK.jpg

Thoughts? I'm having a hard time distinguishing the tracks when it comes to a listening test, getting mostly placebo.


  • What is your question ? – audionuma Jun 14 '16 at 5:22
  • I believe the mp3 specification does not specific how frequency content above 16kHz should be treated, so different encoders may do it differently ("more or less the same" is still not the same...). Note that it is not simple low pass filter, as there is still frequency content above 16K, it's only the low energy content that's purged. – José David Jun 16 '16 at 1:41

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