Hi there,

I know lots has already been written about the quality of VBR vs CBR - especially with regard to the iTunes AAC encoder. What I'm really after (and I'm hoping y'all can help me with!) is something approaching a definitive answer!

I currently only use iTunes for my iPod (I'm still an analogue freak when it comes to home hi-fi) and most of my songs are encoded in AAC - at 256kbps CBR.

There's been lots of debate asto whether VBR is better quality at this bit rate (I understand that at 320kbps there is little or no difference). So basically what I'm asking is:

Is it worth me re-encoding at 256kbps VBR (AAC) - or is 256kbps CBR pretty much comparable in terms of quality?

Many thanks,

TGK

vbr should have higher quality as it will allocate more bits to more complex parts of your music. however at such a high bitrate, it's unlikely you would hear the difference.

i wouldn't re-encode.

One thing for sure is that 256 CBR is inefficient in the following cases :

- Mono or near-mono signals are using twice the normal bitrate
- Different samplerate and resolutions don't know how much quality is needed - 256 cbr is good for 44.1k 2-ch stereo, not for highrez. The user must calculate the correct CBR bitrate in such situation. VBR would auto adjust bitrate.
- A 5 minute silence is encoded @ 256 k cbr instead of a very low bitrate.
- If the psymodel is in trouble CBR stops the bitrate from rising.

Cheers - I reckon it should be okay for the iPod. When I get a digital home hi-fi set-up, I'll guess I'll just have to re-encode everything in WAV anyway.

As I'm using the iTunes AAC encoder, I'm guessing the psymodel is pretty shaky (haven't analysed as yet). Apple will probably never bother to sort it out either.

I think the best thing to do is. Convert your original cd's to apple lossles. (wave only give you bigger files, without better quality)
You can play them on your ipod. And you have a good archive
And for portable use choose aac (Personanly I find 128 vbr pretty good)
Just do some listening test to see if you need higher quality.

++

It's a moot point whether such a high bitrate as you're using is worth it when encoding to lossy; but if you intend to go non-lossy, go for lossless not uncompressed. The latter is only needed if you want to edit sound files. Lossless files have all the information uncompressed files have but, so to speak, in a smaller package.

If you don't want to use those 256kbs AAC files for your home hi-fi encode to FLAC.

http://flac.sourceforge.net/

Alternatively, if you want to use the files on the iPod as well, as the earlier poster suggests, use Apple Lossless. FLAC is far more widely supported across just about all platforms, so a better choice in general, but not, unfortunately, supported on the iPod. My own iPod mostly contains AAC files encoded to 160kbps VBR (Apple AAC) or q0.5 (Nero AAC). That's fine as far as I'm concerned, and you get more on.

Yeah - I'm thinking that way as well to be honest Nick - i.e. encoding at different bit rates for portable and home. It's just a pain to have to do everything twice!

Many thanks for everyone's feedback!

Just to be sure (or maybe you already know) If you converted your cd's to apple lossless in Itunes. You never need your cd's anymore for converting them to a lossly format. Simply convert de apples lossless files to any lossly bitrate you want. Keep the lossles files!
Store the lossles files on a big harddisk. (It's a good idea to also make a back-up of the lossles files, because you put a lot of time in making this files, and it's very frustrating if your drives get's broken)

Good luck!

Just a quick supplementary question then: Do you guys reckon flac is the best lossy codec - in terms of quality - out there at the moment?

flac is not a lossy codec. it's lossless. there is no difference in terms of quality between lossless codecs. their differences are speed, compression, compatibility and features. see this for more info.

Cool - many thanks!

If you plan on living in a iPod/iTunes world then Apple lossless should be fine. You can even accurately rip to Apple lossless using dbpoweramp. EAC can accurately rip to Apple lossless as well but it uses iTunesencode which has to open up iTunes every time you rip a audio CD. dbpoweramp has a built-in reverse engineered Apple lossless encoder making life easier.

Rip to lossless once and never worry about it again, no reason to use WAV as the files take up more space and they can't hold track ID information. Then encode your lossless files to your lossy format of choice. I personally find 128kbps VBR AAC very suitable for portable listening. Even with high end headphone, portable listening environments often don't allow us to hear any benefits of high bitrate audio.

I'd take an educated guess that your files are actually 256kbps ABR since (to my knowledge) you can't configure the iTunes AAC encoder to encode in CBR mode. assuming I guessed correctly, you're going to hear very little to no discernible difference between the files you have now and those encoded in VBR mode (the average bitrates of iTunes AAC files @ 256kbps VBR usually range between 250-270kbps), so I'd just stick with the files you have now.

I think it would depend on what version of iTunes was used to create the files. I'm pretty sure that the default in iTunes before 7.5 was actually CBR. A lot of people are/were annoyed and frustrated that the new encoder in iTunes 7.5 only gives the choice between ABR and VBR_constrained without any explanation or documentation that this changed from pre-7.5.

I think the iTunes AAC CBR encoder has always been quasi-ABR as I remember encoding some files way back when CBR was the only option the bitrate fluctuated in software such as foobar2000 and WinAmp. It didn't fluctuate very much but it still wasn't at the define bitrate for the entire song. I tested about 5 songs, this was back in around 2005 whenever I thought about switching to the iTunes AAC encoder as my lossy library was getting big.

I'll preface this by stating that I'm writing this from memory instead of looking up the information that has previously been posted on this forum, but I'm fairly certain the only AAC profile that uses pure "CBR" with no bit reservoir (as people think of it in the context of MP3s) is AAC-LD. AAC-LC, which is the profile used by iTunes, even when encoding "CBR" has a small bit reservoir, the effect of which being that there will be slight variations in the bitrate, however this is provided for in the ISO standard defining "CBR" for MPEG-4. I'm also fairly certain that AAC does not waste bits encoding silence even when using "CBR" as was stated above. Maybe one of the Nero developers could give a clearer answer.

So again... iTunes pre-7.5 used "CBR" and VBR Constrained while iTunes 7.5 uses ABR and VBR Constrained. To add insult to injury, iTunes pre-7.5 did not report proper bitrates, which made figuring this all out someone of an exercise.

So before I get off my soap box, for what it's worth, I've been disappointed with how the iTunes 7.5 encoder sounds at low bitrates compared to pre-7.5, but impressed with how it performs at high bitrates compared to pre-7.5. I've griped about this in other places around here... including the listening test section... but thus far to no comment. I'm amazed that no one else is noticing/complaining about this.

All that being said, my recommendation to the original poster would be to do some ABX testing to determine if the current files are transparent. If they are, you're done. If they're not and you want to stick with a bitrate of 192 or above, I'd recommend re-encoding with iTunes 7.5 with the VBR checkbox checked or moving to Apple Lossless. If you want to use a bitrate less than 192, I'd reccomend using a pre-7.5 version of iTunes with the VBR checkbox checked.