On Jul 22, 2004, at 11:21 AM, Marcin Wichary wrote:
To convert them you burn the tracks to an Audio CD, then re-rip them back from the CD you burned.
Yes it's lossy, but it's unavoidable.
Lossy? What do you mean?
An audio CD file or AIFF file contains every bit in the digitized music.
MP3, AAC and Fairplay AAC (the ITMS restricted frmat) are all compressed versions of the same music.
You can compress things two ways: lossless and lossy.
Lossless looks to ways of compressing the data in the file in such a way as to retain all the bits, or information in the original. Stuffit and Zip files are examples of lossless compression. These are used for files where every bit is vital, such as programs, or some graphics files like compressed TIFF files.
Lossy compression, on the other hand, looks at the data in the file and determines what is redundant, or at least can be thrown away without too adversely affecting the original. You actually lose data, sometimes significant amounts of data.
JPEG files, for example, use complicated algorithms to determine if, for instance, you would notice a few pixels worth of data being gone, and just 'faked' in the end by guessing at what they are from surrounding pixels. If you have a large patch of yellow, you can throw away most of the yellow, and having the process at the end put yellow in the spot because all the surrounding pixels are yellow.
MP3's and AAC files do something similar with audio data.
There are tradeoffs. Lossless compression is much more limited than lossy; there are hard mathematical limits to how much you can compress things. Lossy methods, OTOH can be far more effective at making a small file; the limit on compression is the acceptable level of distortion in the final product.
This is easy to see when examining JPEG photos.
<http://oscar.pharmacy.arizona.edu/jpegdemo>
This is from a satellite photo of Mount St. Helens.
The top image has had no compression applied to it.
The middle has been set to the middle of the range that Graphic converter offers. There's a noticeable change in the image, particularly in saturation, but it's certainly recognizable.
The bottom image has been set to the maximum compression allowed by Graphic converter. This image is clearly degraded beyond use.
But look at the difference between the first two images. A small amount of image degradation has been traded for a nearly 6-fold decrease in file size.
This sort of compression, btw is behind Sony's claim that their 'iPod killer' can store more songs than the iPod...their default compression is higher than that for the iPod or iTunes.
(This is also the reason that many people think 'MP3 == crap sound' because they're used to MP3's squoze down to the level of giant blue blobs, much like picture number 3...)
--
Bruce Johnson University of Arizona College of Phar macy Information Technology Group
Institutions do not have opinions, merely customs
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