Bit rate fluctuation in iTunes.

[Spikey115]

I have set itunes to encode CDs at AAC 192kbps. When I encode a CD, however, the bitrates are different for each song. Some are at 190 some at 192 some at 194. Range is 183-195. How can I fix this so that all the songs are at the desired 192kbps. I've tried encoding the same disk on a different mac and the same thing happens. Thanks.

 

[Rantipole]

Yeah! This is happening to me too. I have mine set to 160, but songs come back at anywhere from 151 to 162! WTF!

 

[BouncinDave]

It's called VBR, which (i think) is now default on iTunes.

It's actually a better quality file than if you were to rip them into 192kbps each.

However, if you want to fix it, just go into iTunes, Preferences. Then click advanced, and the importing tab. Then press change the setting to custom, and untick the "Use Variable Bit Rate encoding" box!

 

[Rantipole]

Actually the VBR box IS unticked. That's the first thing I checked.

 

[jdavtz]

There was a thread on this a while ago. I think the conclusion was that iTunes now uses something like average bitrate encoding (not variable bitrate encoding, unless you tick the box) rather than constant bitrate encoding.

 

[Rantipole]

I did a search for "average bitrate encoding" and the most pertinent thread seemed to describe it this way: AAC actually never was a "constant bit rate". But somehow iTunes used an "alias" of sorts and put down whatever bitrate you selected. So if you selected 160, that's what it would display, even though it would be ripped at 155, or 162 or whatever.

Can anyone else confirm this?

And, if this is so, being anal-retentive, I wish they would have kept it the other way.

 

[Tom B.]

Now iTunes shows the real bit rate, rather than just the bit rate you chose. Before iTunes 7.5, it would show you the bit rate you selected, despite the fact that some songs would be just above it and some just below. It is now more accurate.

 

[Fuchal]

This is correct. AAC (and most other modern codecs) do not have a true CBR mode. iTunes uses ABR to simulate a CBR encoding, but there will always be an approx. -/+5% fluctuation. Nothing (apart from encoding tweaks over time) has changed between AAC encoding in iTunes, other than iTunes reports the true bitrate of the file.

Also, I would recommend that you turn VBR on to save space/improve quality.

 

[QuarterSwede]

I would recommend that you turn VBR on to save space/improve quality.

Exactly. It's really the best of both worlds.

 

[Rantipole]

Also, I would recommend that you turn VBR on to save space/improve quality.

I don't see how that would save space. Usually, if I when I select VBR, the rip rate is higher than the "target" rate. So, I would get a lot of recordings at 170, 180, whatever, which would certainly take up more space than 160, wouldn't it?

Also, I believe I read somewhere that VBR really doesn't make much difference for Pop music, though it can be worth doing for Jazz and Classical.

 

[Tom B.]

By the way, is it normal that I cannot select 320kbps VBR? Every option except 96, 128, 160, 192 and 256 are greyed out.

 

[Rantipole]

320 is the highest bit rate available for AAC and MP3. So, selecting VBR would do nothing--it can go no higher! The next step in sound quality would come from Apple Lossless or AFLAC.