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Topic: "Constant rate" VBR vs. CBR (Read 4210 times) previous topic - next topic
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"Constant rate" VBR vs. CBR

I encoded the album "Ella and Louis Again" using rev7 standard (after first outputting the wav files as mono).  Every file was either pure 112kbps or so close as to be trivially different (EncSpot shows 100% at 112kbps, with a few little slivers at other bitrates).

Here's a screenshot of one of the "just about" 112kbps files:


My question is this: is there a quality advantage to re-encoding the wav files at --alt-preset cbr 112, or is alt-preset standard doing exactly the same things?  (I don't care about the speed of CBR encoding since I've already encoded the files once).
It's is not, it isn't ain't, and it's it's, not its, if you mean it is.  If you don't, it's its.

"Constant rate" VBR vs. CBR

Reply #1
Quote
Originally posted by Amadeus93
My question is this: is there a quality advantage to re-encoding the wav files at --alt-preset cbr 112, or is alt-preset standard doing exactly the same things?  (I don't care about the speed of CBR encoding since I've already encoded the files once).


Hrmm.. this is hard to say for sure on an album like this but I'd actually trust the vbr more I think because if it is going to need to spend more bits somewhere it should do a better job than abr.

"Constant rate" VBR vs. CBR

Reply #2
Thanks for the response - one more question:  does the fact that it's pegged at 112kbps indicate that it's using too many bits for this content?  Should I do standard with a -b 80 switch, or would that cause other issues?

Or even rev6 normal (with it's bottom limit of 80kbps)?
It's is not, it isn't ain't, and it's it's, not its, if you mean it is.  If you don't, it's its.

"Constant rate" VBR vs. CBR

Reply #3
though I didn't get bitrates neither so low (112) nor CBR-like, I also got very low bitrates when encoding Ella's album (16 Classical Performances). The Album seems to be mono (similar things happened with mono CD version of Beatles' "Help"). Amadeus93 - You can check how many SS vs. MS frames there are (should there be almost 100% MS frames meansthat bitrate is so low because it was mono recording). Also please note (i'm not sure about it though), that 112 is the LOWEST possible bitrate in Dibrom's preset.

"Constant rate" VBR vs. CBR

Reply #4
As I said, I had already converted the wav files to mono, since the original recordings were mono.  I was just wondering if it was possible to lower the lowest bitrate, and furthermore, if it would be advisable.
It's is not, it isn't ain't, and it's it's, not its, if you mean it is.  If you don't, it's its.

"Constant rate" VBR vs. CBR

Reply #5
Quote
Originally posted by Amadeus93
Thanks for the response - one more question:  does the fact that it's pegged at 112kbps indicate that it's using too many bits for this content?


It probably means that it is using more than it would otherwise, but I don't know if "too many bits" would so much be the case if you know what I mean.

Quote
Should I do standard with a -b 80 switch, or would that cause other issues?


Unless you are really dying to save some space I'd just leave it as it is.  But lowering it to 80kbps should probably be OK I think.  I probably wouldn't do it myself though.

Quote
Or even rev6 normal (with it's bottom limit of 80kbps)?


rev6 "normal" shouldn't be used for anything anymore.  rev7 should be superior in just about every way, probably especially on these very low bitrate cases.

"Constant rate" VBR vs. CBR

Reply #6
Dibrom,

I've heard (see source below) that some hardware and software decoders still have problems decoding vbr mp3s that dip below 128 kbps... so why not default -b128 in the current --alt-preset standard?

Does -b112 (the current default) really give you an advantage? Its only 16 kbps difference.

I mean there is no chance that -b128 could decrease quality, right?

SOURCE:
http://privatewww.essex.ac.uk/~djmrob/mp3decoders/vbr.html

"About 1/4 of these decoders fails this test
VBR files are more compatible if the bit-rate doesn't fall below 128kbps..."

Any other comments from anyone else?

"Constant rate" VBR vs. CBR

Reply #7
Quote
Originally posted by RD
I've heard (see source below) that some hardware and software decoders still have problems decoding vbr mp3s that dip below 128 kbps... so why not default -b128 in the current --alt-preset standard?


Hrmm.. well this is a possibility.  I've been toying with the idea of just defaulting 128kbps for the lower end for all vbr presets for awhile now, I just haven't really decided for sure.  Realistically, it isn't going to affect bitrate except for on extremely quiet clips like rach_original, or something like the ones shown above, and maybe that's actually a good thing anyway because then it should further prevent them from dipping to low (although they should be fine anyway).

I wasn't even aware of the information at the link you posted so I guess that's just further reason why it might be a good idea.

I guess if nobody has any objections to this (and can give me a good reason why I shouldn't do it) I'll go ahead and do it.

Quote
I mean there is no chance that -b128 could decrease quality, right?


I don't believe so.

"Constant rate" VBR vs. CBR

Reply #8
Quote
Originally posted by Dibrom

I guess if nobody has any objections to this (and can give me a good reason why I shouldn't do it) I'll go ahead and do it.


The only reason I can think of off the top of my head is encoding a movie soundtrack for use with DivX... Then, the bitrate will drop below 128 quite often in most cases. But as long as you can just suffix a -b96 option to override it I can't say I mind, seeing as it won't change much for music encoding...

"Constant rate" VBR vs. CBR

Reply #9
Hi Dibrom,

I see that as of December 18th you have not changed the -b112 to -b128 in --alt-preset standard.

Is there a reason? Did the -b128 affect quality or something else after all?

Thanks,
curious,
RD

 

"Constant rate" VBR vs. CBR

Reply #10
fixed.

 
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