Conversion from AAC 320(VBR) to AAC 320(CBR)

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Conversion from AAC 320(VBR) to AAC 320(CBR)

Hello --

I have a question regarding using iTunes to convert a AAC 320(VBR) (variable bit-rate) file to an AAC 320(CBR) (constant bit-rate) version. When using the built-in iTunes conversion algorithm, will it treat the parent file (the AAC 320 (VBR) file) as a lossless file, and then downsample to creat the AAC 320 version? Or will it go 'across the board' and treat the parent file as an already downsampled file, and just make a file without the VBR label? The files were imported via iTunes, and I must have had the VBR box checked when doing the import.

Namely, I just don't want to lose any audio quality when doing a conversion - most of the files are classical musical files, and as such, I can notice the difference in the audio of lower bit-rate files versus true lossless or 320 bit-rate formats, at least when played over high-end speakers.

Normally when doing a VBR import, the actual bit-rate will change per song (as far as I've experienced, say one song is 289, the next 274, etc.) and all of the songs that I have talking about are 320 (VBR) quality. I'm assuming that iTunes imported them all at a 320 constant bit-rate, but labeled them as VBR regardless due to the checked setting in the import settings; I had the other import settings maxed out at highest quality otherwise (aside from the AIFF file format, which I know is true lossless).

Thanks!

MacBook Pro (15-inch Early 2008), OS X Mountain Lion (10.8.3)

Posted on Mar 18, 2013 10:23 AM

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Answer 1

Mar 18, 2013 10:51 AM in response to carlgebeling

carlgebeling wrote:

When using the built-in iTunes conversion algorithm, will it treat the parent file (the AAC 320 (VBR) file) as a lossless file, and then downsample to creat the AAC 320 version?

Since this is not a lossless file, no.

carlgebeling wrote:

Namely, I just don't want to lose any audio quality when doing a conversion -

Going from lossy to lossy you will lose audio quality. Now, whether you can actually hear that loss or not is up for debate, but cross converting from lossy to lossy is generally not a good idea if your purpose is to not lose quality. Your best course of action is to re-rip the tracks from the CDs.

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Answer 2

carlgebeling Author

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Mar 18, 2013 1:52 PM in response to Michael Allbritton

Hi Michael --

Thanks for the response. I figured that any invocation of the iTunes conversion tool would result in a down-sampled file. I was hoping for a smarter algorithm that could detect the inherent bit-rate of the source file, but if the algorithm inherently downsample regardless, then yes, I will need to just re-import, since I don't want to lose audio quality.

Thanks...

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Answer 3

ed2345

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Mar 18, 2013 7:58 PM in response to carlgebeling

I figured that any invocation of the iTunes conversion tool would result in a down-sampled file..... if the algorithm inherently downsample regardless, then yes, I will need to just re-import, since I don't want to lose audio quality.

Carl,

Format conversion in iTunes does not down-sample the file. Unless you force a change by setting the options, the sample rate remains whatever it was, which is usually 44.1 kHz.

As Michael notes, converting one lossy format to another may entail a loss of audio quality. Is there some reason you don't just keep the AAC/320 VBR files that you have?

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Answer 4

carlgebeling Author

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Mar 19, 2013 6:49 PM in response to ed2345

ed2345 --

Thanks for the reply, I appreciate it. I was mainly just wondering for my own sake - and I'm kind of (yes, I'll admit) OCD; I have decided to downsample from lossless to save a bit on laptop hard drive space, but I still connect to high end speakers (either through wireless into high-end DAC converters, or directly) so it's nice to have as high of quality of a downsampled file for the audio quality.

Thanks again for the reply!

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Answer 5

Chris CA

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Mar 19, 2013 7:16 PM in response to ed2345

ed2345 wrote:

As Michael notes, converting one lossy format to another may entail a loss of audio quality.

To be correct, converting from ANY format to a lossy format, you will lose quality.

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Answer 6

Chris CA

Level 10

82,434 points

Mar 19, 2013 7:28 PM in response to carlgebeling

iTunes VBR is almost always better quality than iTunes CBR.

And VBR is usually smaller than CBR since the bit rate will go down with less complex passages. CBR will use the same bit rate setting for the entire track, whether it needs those bits or not.

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