Author Topic: Mp3 VBR and "bitrate" in file info  (Read 5000 times)

diego59

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Hey. I was wondering if someone here knows: in a mp3 VBR, the file has in its information a determined bitrate. What does this bitrate mean if the file is in VBR ?
For example, a VBR 0 has a 166 kbps, but oftenly a VBR 0 has more than 220kbps.

hiccup

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That will be dependent on the complexity of the audio that has to be encoded.
A complex piece of music will require a higher average bitrate than for example some simple 'computer beeps' to reach the required quality.

diego59

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And for example, if I have a mp3 320kbps CBR, and convert it to mp3 VBR 0, if the mp3 in CBR was in 320kbps, but in fact was of less quality (lets say it was put at 320kbps but before that was in 160kbps CBR). The VBR 0 algorithm will take that mp3 and the result is according to the real quality, so it will show the kbps info at 166 kbps?

My question is, if I have 2 songs that doesn't differ much in "complexity", at 320kbps CBR, and convert to VBR 0. Why one of those two take down to 166kbps while the other one takes to 230kbps? In the file info.

hiccup

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I can't tell you exactly, but I could imagine that it might for example be 'easier' to re-encode a high quality 320kbps sine-wave to VBR0, than it is to re-encode a 160kbps sine-wave that already had some more 'damage' to VBR0.

Regarding your second question, I am not sure how reliable you would be able to decide that you have two songs that would be similar in complexity to re-encode.
For example one track could have more high-frequencies that are difficult to notice by ear, or ambient reverb, or a hardly perceivable 'soft noise' in the background.
Even though your ears would have difficulty discerning those, the algorithm will have to handle all that information.

You might want to check out the Hydrogenaudio Forums if you want to get down to the nitty-gritty of this subject.
There is a lot of knowledge on stuff like this over there.