I am writing this in advance of the upcoming (0.9q) bitrate indicator for MP3, which does not workout as intended, or better, the promised bitrates in MP3 files do not work out ...
On another note I personally wonder what is going on;
What XXHighEnd does, is calculate the effective (!) bitrate opposed to the filelength and the duration (play time of the track). With this, the sample rate (44100) and bit depth (16) is assumed. Now, CBR (Constant Bit Rate) 320 Kbs (as officially indicated in the file header) files turn out to be anything in between 224 and 320.
Files, officially indicated as 256 can also turn out to be (near) 320, although this is more rare (i.e. usually the effective bitrate is lower than indicated).
I did not try to create MP3s myself in order to find out what's really going on, but is this a known phenomenon ?
Are we possibly hoaxed at downloading files with a presented too high bitrate ? (think of AllOfMP3 -> MP3Sparks where you pay more the higher the bitrate).
Am I missing something ?