capmorgan

 

Hi musikone

Thanks for your response. Continuing the discussion ....

 

 

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However, when I create an audio CD using AAC tracks from iTunes, on the CD the tracks become full size files again.

 

So, my question is if compression was achieved by eliminating portions of the audio track how come when the same audio track is burnt onto a CD, it becomes a full size file again?

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A compressed file can be expanded to _simulate_ the file before it was compressed--except for.....(read on). For example, an mp3 file can be "converted" to a much larger wav file. Note the quotation marks!

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capmorgan: hmmm. So what would someone gain by converting an mp3 file to a wav file? If the track has been compressed to mp3, which is a lossy compression, I don't quite see the reason someone would want to convert an mp3 to wav. The resulting file would only be larger and there would be no gain in quality.

 

Coming back to my iTunes example. I take the AAC tracks from iTunes and burn an audio CD - do you know what format the tracks on this CD are? I originally thought they would be CDA as in the original CDs. However after reading your earlier response, I gather this can't be right since I'm burning compressed tracks onto the CD. Are they just AAC format but altered so that they can play on regular CD players?

 

 

Now, about Wav files - is this format a lossy compression, non-lossy compression or orginal (non-compressed) quality?

Wondering what happens when I convert a CD track to a Wav file.

 

 

again, thanks a lot for your help.

cheers

Hello all,

I'm trying to understand something about compression.

I know that CD tracks are pretty big files and when they get imported into iTunes (with AAC compression) the tracks get "shrunk" to pretty small file sizes.

From what I read, compression is achieved by eliminating "unnecessary" bits of an audio track. To my mind if certain portions of an audio track are eliminated they're gone forever .. right? However, when I create an audio CD using AAC tracks from iTunes, on the CD the tracks become full size files again.

So, my question is if compression was achieved by eliminating portions of the audio track how come when the same audio track is burnt onto a CD, it becomes a full size file again? Do the eliminated bits somehow come back to life in the CD burning process?

Isn't compression an irreversible action?

Is all of the above specific to AAC and CDA or is that how compression works in general - ie unnecessary bits are not really eliminated, they're just kinda hidden?

This brings me to another question - when an AAC track is played back - am I listening to the compressed version or the full version?

I've read quite a few articles on compression but they are all so technical and talk about the algorithms of compression (whatever the heck that means) but I just can't seem to find an article that ties together in layman terms compression, playback and "uncompression" if you will.

Any light shed on this will be greatly appreciated.

Cheers!