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Topic: Differences between mp3 V0 and mp3 320kbps (Read 42926 times) previous topic - next topic
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Differences between mp3 V0 and mp3 320kbps

Hello,

I'm interested in learning the differences between the mp3 V0 and mp3 320kbps audio file types. I have a basic understanding of sampling and understand that the mp3 320kbps scheme samples at a fixed rate of 320 kbps while the V0 type samples at a varying rate, depending on the density of information at a given point in the song. I'm under the impression that the main method of compression that the V0 type uses is that it eliminates higher frequency information when the song doesn't contain high frequency content. Am I wrong about this? What else does the V0 type do that the 320kbps type doesn't?

Thanks in advance

Re: Differences between mp3 V0 and mp3 320kbps

Reply #1
I'm under the impression that the main method of compression that the V0 type uses is that it eliminates higher frequency information when the song doesn't contain high frequency content. Am I wrong about this?

Yes, that is not correct. 

What else does the V0 type do that the 320kbps type doesn't?

It changes the bitrate based on what is present in the audio using less bits if there is less to encode.  Otherwise, there is not much difference.  CBR 320 files can often be losslessly repacked into roughly V0 bitrate files. 

Re: Differences between mp3 V0 and mp3 320kbps

Reply #2
Thanks to bit reservoir native V0 files may be of higher quality than (repacked) CBR 320 files.

Re: Differences between mp3 V0 and mp3 320kbps

Reply #3
Thanks to bit reservoir native V0 files may be of higher quality than (repacked) CBR 320 files.

I know this is an older post.

It's my understanding that thanks to the bit reservoir, a 320k CBR file might be of higher quality than -V0 but that in practice, few would notice and that it's more correct to use -V0 and let the encoder decide because more often than the additional bits available to the reservoir being of use, the encoder will have no use for the rest of a frame and insert useless padding to keep the user (who requested 320k CBR) happy, or encode data that's not terribly important to perceived quality just because it has the room to store it.

However, this is not necessarily always the case. I found some 320k CBR files of some Adventure Time soundtracks and tried to use mp3packer on them, and most did not have any real reduction in size. The average bitrate remained at 306 kbps - 319 kbps.

I believe that there is no lowpass filter applied at 320k CBR (at least by LAME 3.98 and later) because it has plenty of data to work with and the global gain probably won't be adjusted too much just to accommodate it at  that bitrate, which is probably why there's not much padding.

Seems LAME's older psy model (the one in 3.97 and older) produced 320k CBR files that used a lot of padding and were more likely to yield significant savings if you used mp3packer.

 
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