Does Encoding AAC Files in iTunes with VBR on Improve Audio Quality ?

Are there Disadvantages ?

Usually, an 'auto' type encoding tool will screw up the natural flow of the music and miss subtle changes in the energy, volume, etc.. -stuff that is just to subtle for it to catch -Generally I wouldn't trust an 'auto' type setting to pick up this subtle stuff. Yet people say using VBR improves sound quality (and NOT file size). Why and how ?

What is the max bit rate VBR uses ? If I set my AAC encoder to 320 kbps and turned VBR off, wouldn't the sound quality be superior to encoding with VBR on (simply because the kbps are set at 320 the whole time...) ? Sure, the files encoded with VBR off would be larger, but wouldn't the quality be better ?

Lastly, I did a little test and encoded one song with VBR off and one with VBR on. The VBR song was 1.5 MBs bigger - Huh, I thought, is that increased file size the result of improved resolution throughout the whole song, or just one little section (haven't had time to listen to them)?

Thanks in advance-

T

first off all, you shouldn't notice quality differences at those high-bitrates. VBR is just an efficient way to store the bits - some samples needs less bits to be encoded and some other samples need much more bits to be encoded. That way you will save bits where you don't need, and this is a major advantage. VBR should be smaller compared to the same fixed CBR bit rate. Unless you have something very wrong with your setup and you're not following HA pinned recommendations, you should be just fine.

Thank you for responding -


Actually the VBR files are almost always bigger...don't know why, here's an example (Its from the Album Sabroso!):

Track 17 Oriza.m4a:

Using iTunes 7.0.2, 256 kbps, 44.100 khz, stereo: --8.8 MB
Using iTunes 7.0.2, 256 kbps, 44.100 khz, stereo with VBR on: --9.4 MB

Track 11 Viva Cepeda.m4a:

Using iTunes 7.0.2, 256 kbps, 44.100 khz, stereo: --6.8 MB
Using iTunes 7.0.2, 256 kbps, 44.100 khz, stereo with VBR on: --7.6 MB

Don't know what "HA pinned recommendations" are, just using iTunes -

Any other thoughts on the above questions would be greatly appreciated -

T

CBR = constant bitrate, variable quality
VBR = variable bitrate, constant quality

The pinned recommendations are here:
http://www.hydrogenaudio.org/forums/index....showtopic=44310

VBR files can be bigger, since frames with more bitrate (like 320) can be used and will be used, if the encoder thinks the input signal requires this for a given quality level. This shows that the encoder recognized a difficult to encode passage and is giving it more bits to avoid audible problems - CBR would always assign the same number of bits and may therefore sometimes use too much (waste of space) or too few (quality problems) bits.

BTW, you really should try a double blind ABX test to determine the bitrate you really need - you might be surprised:
http://www.hydrogenaudio.org/forums/index....showtopic=16295

For instance, I use HE-AAC on q0.17 which is about 48kbits for my mobile w/ headset and traffic noise, which in this circumstances sounds really good in most cases.

From what I remember of the various posts already on HA, what iTunes calls VBR is actually a quasi-VBR mode where more bits may be used for more complex frames, with the selected bitrate being a minimum bitrate for any frame, e.g. if you select 128 VBR, iTunes will allow a higher bitrate where necessary, but 128 will be a strict minimum for any frame (I can't remember how if handles silence).

Therefore, if you use VBR in iTunes, you will get a file with constant quality, but it will almost always be larger than its CBR counterpart.

I've had good luck encoding at 128 VBR, however you should let your ears be the judge.

This is correct. If you encode a file that has moments of silence, you'll see that the bitrate of an iTunes "VBR" encoded file very rarely dips below the specified average bitrate. I use Nero's AAC encoder and I've got it set to encode at q 0.45. I've got files that average 200kbps, and files that average 88kbps (and just about everywhere in between). It really depends on your source material, but iTunes' current VBR implementation is a bit backwards when you think of what VBR is intended to do (maintaining quality while keeping filesize to a minimum).