Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[RussellS]

I have just been converting my music library which contains a mixture of flac, ogg & mp3 files to purely mp3 to put on a memory stick for use in the car. I have the mp3 encoder setting set to 'VBR Encoding' and the target quality set to 'High' and I am a little surprised and a little concerned at the results.

Quite a few of the resulting converted files have ended up with a bitrate as low as 80 to 120. How can this be the case with the target quality set to 'High'.

Am I misunderstanding something with regards to VBR encoding or is there a problem somewhere. If this is the case could someone enlighten me please.


Thanks for any info on this.

[Hendrik]

There should be an "Extreme" preset for the highest possible quality, if i remember correctly, or 320 kbps CBR.

Otherwise, we just tell our MP3 encoder to use a high quality preset, and for VBR it actually depends on the audio itself how well it compresses and how small the resulting file will be. Some audio just compresses much better than other audio.

[RussellS]

Thanks Hendrik, I just thought that 80kb/s didn't equate to a high quality MP3.

However, having thought about it a bit, when the tag says a bitrate of 80 I don't know if that is referring to the average bitrate of the file or the minimum bitrate etc. So if using VBR files it is probably not a good idea to use the bitrate as an indication of audio quality the same as you would with a CBR file.

[Dorsai]

Mono recordings will result in low VBR, so that is one possibility.

[BartMan01]

MC uses L.A.M.E. for MP3 encoding.  If you are picky about the encoding options, you can geek out and use the custom command line switch to specify exactly how you want encoder to process the files (http://lame.cvs.sourceforge.net/viewvc/lame/lame/doc/html/detailed.html).  The WIKI article is way out of date on this.  It would be nice to have current documentation on what version of LAME is being used and what the target quality settings are actually doing from a parameters standpoint. 

Personally, I switched to APE then later FLAC years ago and only use MP3 now for portable listening.  I use the default 'normal' setting in MC, and have not seen any reason yet to change that.

Depending on the parameters used, LAME shoots for a target average bit rate with VBR - but the final average bit rate is very dependent on the content.

FYI - looking at recent files done by MC with the 'normal' setting I am seeing the following info in the file:
Writing library : LAME3.99r
Encoding settings : -m j -V 4 -q 0 -lowpass 17.5 --vbr-mt -b 32

Per the -V 4 it is shooting for an average bit rate of 165.  Looking at two tracks: a mono Beatles track came it 91 while a high res FLAC from Linn (from their latest 24 bits of Christmas) is at 166.

[BartMan01]

So if using VBR files it is probably not a good idea to use the bitrate as an indication of audio quality the same as you would with a CBR file.

Correct - if you play a VBR encoded file back in MC you can see the bitrate changing at the top to see what bitrate different sections are actually using.  With VBR files, the 'bitrate' field in the file indicates the overall average bitrate.  Specific sections of the content may drop way below or jump way above that average.  With CBR, you need the constant bitrate set high enough to handle the most complex part of the track.  With VBR, it uses the higher bitrate only when needed resulting in a smaller file size with the same quality of a higher CBR version.