VBR vs. CBR same file size quality

2009-08-14 19:04:28

Hi!

I am newbie and well, you heard this question before, but I still doesn´t quite understand the difference in quality of the files with the same file size. For example: V2 190 vs. CBR 190, or  CBR 245 vs. V0 245. Can someone please tell me the difference, because this statemen from http://wiki.hydrogenaudio.org/index.php?ti...onstant_Bitrate still confuses me:

"... VBR will almost always produce equal or better perceived-quality results than CBR for files of the same size or average bitrate"...

What am I missing here?

VBR vs. CBR same file size quality

Reply #1 – 2009-08-14 19:23:50

Regarding VBR, any quoted bitrates are guides/averages, which were presumably derived from test filesets. VBR targets a given quality (transparency) level, not file size.

However, for explanation's sake, assume two hypothetical MP3 files: one at 192 kbps CBR, and a -V2 file with an average bitrate of the same. The benefit of VBR is that less complex frames can be encoded with lower bitrates, which 'frees' some of the average bitrate to encode more complex passages at other points in the source file.

VBR vs. CBR same file size quality

Reply #2 – 2009-08-14 19:25:57

First of: If you're a newbie and don't want to give this too much thoght, use -V 0 and newest LAME version and forget about how it works and what settings are better!

Sencondly, if you're really interrested, with the potential to become overly obsessed with all the details (like I was or still am, hehe), then read on.

VBR is better mainly because it can use very few bits for encoding very easy parts of audio, like maybe 32 kbps and because of that it has the ability to use 320 kbps on parts that are more complex and therefore you get perfectly good quality for the easy parts and the best quality possible for the complex parts.
CBR on the other hand, must use constant bitrate, even for those easier parts that would require less kbps than the CBR setting. Every CBR below 320 kbps therefore can not use 320 kpbs for those complex parts mentioned and will encode those worse than VBR mode, which has some reserve, because it used fewer bits with the easy parts and it must only achieve some average bitrate in the end...

I hope I explained this the easiest way possible. The conclusion would be: CBR is more straightforward, VBR is more flexible. Flexible is good, because it can adjust to your needs.

edit: typo

VBR vs. CBR same file size quality

Reply #3 – 2009-08-14 22:33:00

Say you have a classroom of 24 students and you need to divide them into 6 groups to do group work on 6 different art projects.

You regulate that each group consists of 4 students, and then arrange them into their groups based personality and familiarity so that they work best in groups of four, then you have a constant student rate of four students per group.

If you decided to take your 24 students and arrange them into 6 groups so that they work the best they can, (e.g. maybe one or two groups has 5 students and and another one or two has 3) then you have an average student rate of four students per group, but they'll be turning in better quality work.

If you decide that they most important thing is that these 6 art projects be completed at the same quality at a quality level which you specify, then you might decide that pre-confining yourself to 24 students is either, too many (for easy projects) or too few (for difficult projects) and therefore you might lend or lease students to and from different classrooms. You now have a variable student rate but a hopefully constant quality rate for your art projects.

I hope that helps.

VBR vs. CBR same file size quality

Reply #4 – 2009-08-14 23:25:56

Thanks a lot for the answers guys! 

So, now if I understood correctly, this means that VBR files are better in quality then CBR files with the same bitrate (exept the highest CBR bitrate possible like 320), is that true?

regards,
 

VBR vs. CBR same file size quality

Reply #5 – 2009-08-14 23:43:19

That's correct.