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Topic: AAC VBR vs AAC CBR vs AAC ABR (Read 74466 times) previous topic - next topic
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AAC VBR vs AAC CBR vs AAC ABR

hey guys i have some hip hop cds that i have been collecting that i want to rip into my itunes library. i am currently using x lossless decoder for mac with the aac codec. i was wondering what is the difference bewteen vbr, abr & cbr. which one of these encoders provide the best maximum quality? i dont want to convert my cds to flac because i dont want to take up much space. So please tell me which encoder is best for quality; cbr, vbr or abr. thanks

AAC VBR vs AAC CBR vs AAC ABR

Reply #1 –
CBR is constant bit rate.  Every packet of data will be a fixed size (+- 1) so that a fixed amount of data is produced from the encoding process.  If the music you are encoding is "simple" and can fit well within the bitrate, then extra space is wasted.  If the music you are encoding is "complicated" and cannot fit in the bitrate, quality is sacrificed.

VBR is variable bit rate.  The packet size varies depending on how much data is needed to achieve a desired quality.  "Simple" music of a same duration will be smaller than "complicate" music of the same duration.

MPEG-1 layer 3 (aka mp3) can be CBR or VBR.  The standard specifies that packets of a certain bitrate will always be a specific calculable size.  MPEG-2 nbc (aka aac) does not make a specification of packet sizes, but instead specifies an Average bitrate that should be achieved (ABR).  In this regard ABR and CBR are very similar in that they will achieve a mostly predictable file size at some potential sacrifice in quality.

So:
MP3 can be encoded in CBR or VBR.  AAC can be encoded in ABR or VBR.  ABR/CBR will give you a predictable size, but may sacrifice some quality if you set your bitrate too low.  VBR may give you better quality, but your file sizes may not be so predictable.  You may find yourself tweaking more knobs with VBR, but you may be more satisfied with the results.

AAC VBR vs AAC CBR vs AAC ABR

Reply #2 –
mp3 can be ABR too.

If you want quality but hard disk space is issue, go for VBR. Size of each file will vary, but avarage filesize of entire media library can be estimated.

AAC VBR vs AAC CBR vs AAC ABR

Reply #3 –
CBR / ABR doesn't automatically 'sacrifice' quality. Encoders can make use of a bit reservoir like mp3. Also : The quality advantage of VBR is not proven for high bitrates (above 128k)

When filesize predictability is desired ABR / CBR 160 kbit  or more can work very well. Otherwise there is also little reason to avoid VBR of a well tuned encoder when you want robust quality without regard for filesize.

AAC VBR vs AAC CBR vs AAC ABR

Reply #4 –
Quote from: shadowking on
The quality advantage of VBR is not proven for high bitrates (above 128k)

I have a feeling this will strike many of us as quite a revolutionary concept.  Please do elaborate...

AAC VBR vs AAC CBR vs AAC ABR

Reply #5 –
Quote from: greynol on
Quote from: shadowking on
The quality advantage of VBR is not proven for high bitrates (above 128k)

I have a feeling this will strike many of us as quite a revolutionary concept.  Please do elaborate...



That the current CBR quality starvation claims are really similar to old VBR claims that quality will 'jump up and down' with bitrate and therefore should be avoided.

AAC VBR vs AAC CBR vs AAC ABR

Reply #6 –
guys i dont care about predictable file size or any shits! i just want the best decoding option for the aac encoder. either abr, vbr or cbr.

space isnt a problem! i just want to rip my  cds into great itunes quality! better than the one in itunes store. please im a dummie! i dont need all the technical stuff. just one word answers!

AAC VBR vs AAC CBR vs AAC ABR

Reply #7 –
Quote from: loneranger76 on
guys i dont care about predictable file size or any shits! i just want the best decoding option for the aac encoder. either abr, vbr or cbr.

space isnt a problem! i just want to rip my  cds into great itunes quality! better than the one in itunes store. please im a dummie! i dont need all the technical stuff. just one word answers!



Space isn't a problem but lossless is... OK

AAC VBR 224k is a good setting that has a slight safety margin if you are not going to use lossless. 320k is also quite acceptable IMO if your ripping to lossy but not much higher.

AAC VBR vs AAC CBR vs AAC ABR

Reply #8 –
some say vbr and some say cbr idk wat to chose. i want my rips to be identical to itunes store. they rip at 256 kbps and thats what i want to rip at! and i want best quality. please shud i use vbr or abr or cbr.

AAC VBR vs AAC CBR vs AAC ABR

Reply #10 –
Quote from: loneranger76 on
some say vbr and some say cbr idk wat to chose. i want my rips to be identical to itunes store. they rip at 256 kbps and thats what i want to rip at! and i want best quality. please shud i use vbr or abr or cbr.


If you want to get identical quality to iTunes Store, you should use the iTunes Plus (+) setting: iTunes/QuickTime AAC Constrained VBR Max Auto 256 kbps, http://www.hydrogenaudio.org/forums/index....showtopic=70405

However, I prefer CoreAudio/QuickTime True VBR AAC encoding. You can access to this mode through XLD on Mac OS X or qtaacenc on Windows. For more information visit the following posts:

- qtaacenc: a command-line QuickTime AAC encoder for Windows
- Has the iTunes AAC encoder changed recently?
- Snow Leopard AAC improvements..

Regards 

AAC VBR vs AAC CBR vs AAC ABR

Reply #13 –
Heh, just joking around. At least you quoted the setting; that should suit the OP, who seems to just want to be told what to do, rather than do any reading...

AAC VBR vs AAC CBR vs AAC ABR

Reply #14 –
Quote from: dv1989 on
Heh, just joking around. At least you quoted the setting; that should suit the OP, who seems to just want to be told what to do, rather than do any reading...


OK, no problem.

Regards.

AAC VBR vs AAC CBR vs AAC ABR

Reply #15 –
Quote from: loneranger76 on
space isnt a problem!


Then go for ALAC. Lossless = max quality, but also requires max space.

Otherwise, MP3 VBR v0 is excellent, and keeps you from wasting space. Don't cling to the romantic idea of the itunes store, but find things out for yourself.

Quote
please im a dummie! i dont need all the technical stuff. just one word answers!


You may be a dummy now, but once you cross the threshold and step into the wonderful world of ripping and encoding, it really pays off to learn some details about the different formats, processes, software etc. Even if it's just to prevent yourself from being befuddled, bewildered and bamboozled by faulty advice.

Stick around. Read some threads.

AAC VBR vs AAC CBR vs AAC ABR

Reply #16 –
Quote from: shadowking on
That the current CBR quality starvation claims are really similar to old VBR claims that quality will 'jump up and down' with bitrate and therefore should be avoided.

What does this have to do with your nonsensical notion that quality benefits above 128kbits with VBR have not been proven?

AAC VBR vs AAC CBR vs AAC ABR

Reply #17 –
Exactly that . They haven't been proven. There are no quality scientific tests the show big superiority of VBR at high bitrates .

AAC VBR vs AAC CBR vs AAC ABR

Reply #18 –
Are you trying to say that I cannot find a single track in my collection that is transparent above 128kbits that wouldn't also be transparent at 128kbits?



EDIT: While I don't use AAC, I can find dozens encoded with Lame 3.98.  I would never think to claim that this is impossible for AAC.

AAC VBR vs AAC CBR vs AAC ABR

Reply #19 –
Quote from: shadowking on
There are no quality scientific tests the show big superiority of VBR at high bitrates .

Are you saying that LAME encodings in VBR at, say, -V0 are sonically no better than using the same encoder in CBR at 128kbps, and that every time the encoder makes the decision to use bitrates above 128kbps in VBR these decisions are wrong? That's the way it's coming across to me, and, based upon personal ABX tests, I'd have to strongly disagree. 

AAC VBR vs AAC CBR vs AAC ABR

Reply #21 –
It happens again and again: as soon as one of the major beliefs on HA (such as 'VBR is best') is addressed here as questionable reactions are like those here.

shadowking didn't but say that there is no proof that VBR is superior at high bitrates. That's simply true because it can't be proven. There's not even even a strong evidence for it.
Few years ago in a low bitrate listening test WMA professional CBR came out second best, outperforming several VBR encoders in terms of quality (which in contrary is no evidence that CBR is best).
Bit reservoir helps a lot making even CBR a variable audio data procedure.

Whether VBR, ABR, or CBR is best will also be a question of the encoder used. As for the OP's question concerning AAC I think nobody can give a real answer. We can only have a feeling towards it, and for most of the HA members this is probably in favor of VBR.

I personally would use VBR too with Nero or Apple AAC.

For the OP's question about the difference of VBR/ABR/CBR:
mp3 and aac encoders separate the music stream into single 'frames' of music. Each frame corresponds to a short interval of the music of very roughly 1 msec (exact details vary with the format and the musical content). Each frame is encoded separately. The first thing to know is when talking about CBR, ABR or VBR that this addresses frame bitrate. With CBR encoding bitrate is identical for every frame. With VBR it's not necessarily so. ABR in this respect is a VBR encoding mode as frame bitrate can vary.
frame bitrate is not identical with audio data bitrate because of the concept of bit reservoir. If the data space provided by the current frame bitrate is not totally needed (according to the encoder's accuracy estimation) the unused space can be used for the audio data of the next frame(s) - within certain restrictions. That's why even CBR is a variable audio data procedure.
Another important aspect is the usual way audio data accuracy is controlled. This is identical for ABR and CBR (ABR just releases the restrictions imposed by the bit reservoir as well as the limited discrete steps in choosing target bitrate), but VBR is different. With VBR the psy model is used for the accuracy control, for CBR/ABR this is so to a minor degree. As a consequence VBR quality relies more on the underlying psy model having no flaws. With CBR/ABR this is so to a minor degree. Roughly speaking when the psy model used is great then VBR should be the more intelligent approach leading to more efficient encodings. High bitrate CBR/ABR on the other hand can overcome to a certain degree flaws in the psy model.
Another point is experience and testing. If most experience for an encoder is with say VBR, and experience is good, this is an important point for using VBR.
So I guess in case of Apple AAC the most promising way is to do it the way Apple does it with its 256 kbps iTunes store music.
lame3995o -Q1.7 --lowpass 17

AAC VBR vs AAC CBR vs AAC ABR

Reply #22 –
Quote from: halb27 on
shadowking didn't but say that there is no proof that VBR is superior at high bitrates.


What is superior to what, specifically? What I read so far is that VBR with unmentioned settings is not proven to be superior to an unmentioned CBR, both produced with an unmentioned encoder (though we assume LAME).

That kind of statement doesn't exactly strike me as a sound basis for discussion.

AAC VBR vs AAC CBR vs AAC ABR

Reply #23 –
Quote from: halb27 on
That's simply true because it can't be proven.

Nonsense.  It takes but just one sample to shoot his claim down in flames.

Otherwise there is absolutely no need for settings that create files with a bitrate larger than 128kbits and therefore Apple's iTunes Plus is a waste.

AAC VBR vs AAC CBR vs AAC ABR

Reply #24 –
Which would only prove that for this sample VBR is the better choice.

The problem is that for usual music and a good encoder and a sufficiently high bitrate VBR, ABR and CBR will all provide excellent quality.
And for the small world of problem samples it's hard to even give evidence for a specific method is superior.
lame3995o -Q1.7 --lowpass 17