What I meant to say is that there is no generic means of compressing data losslessly to 2:1 (a la the WINZIP example). Now for a specific context of data (say audio files) you could come up with an encoding scheme that might achieve a better compression ratio, because the data has a fixed context and tends to be more predictable. You mention the iTunes encoder. There is also the FLAC encoder which is actually free.
You will see that even these encoders average >50% (except one) although they are all less than 60%. But look at the numbers for specific songs and you can see significant various based on the type of music. For some songs the ratio rises to 60+% whereas for some other songs the ratio drops to as low as 30+%. In fact, from the looks of it, it seems that classical music compresses better than pop music?
Just to clarify Filper's remark. MP3s CANNOT contain more than 2 channels. It is not in the spec. I believe WMA can contain more than 2 channels. Though I have never heard one. Not sure about AAC, but I would think it would.
I was using the WinZip as an example of lossless compression. I was not impling that we could use it on WAV files to save space!
As you have said, usng the proper encoder can save 50% without any loss of the digital signal ie APE, FLAC, WMA, etc
Anyone who wants to transfer their CD collection to MP3 (or whatever) should take one or 2 titles, rip them using various bit rates and sit down and decide which is the best for them. I did that and settled on the 320 VBR using the lame decoder. I think "most" people would be happy with that.
On a side note, for anyone looking to digitize their CD collection my only advice (and the best decision I personally made) would be to keep a lossless rip of your CDs... it's worth the hard drive space. As codecs improve and change you'll thank yourself as re-encoding is far easier if you've got the lossless files and don't have to feed your CDs through your PC - again!!
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