Ok, so, if someone could finally answer this question once and for all, and back it up with logic or quantifiable data, I’d appreciate it, because everyone seems to have a different opinion:
When sound tracks in ordinary CD format are compressed into Mp3s, there is a negligable loss in quality, which is either impossible or extremely difficult to pick up audibly. This, as far as I know, has not been disputed (anyone have anything to say about that?).
Now, once the Mp3 is expanded and burned onto a regular audio CD, that loss in quality remains constant, although it’s once again almost unrecognizable.
So…the question is: if I take this audio CD that was burned from Mp3s, and go through the same process of ripping that CD BACK into Mp3s, does yet ANOTHER miniscule loss of quality occur? Does this happen every time this process occurs, to the point that a noticable difference can occur? OR, is it the case that once the initial transfer occurs, whatever loss of quality that is part of the initial process is the final and last change to the format, causing the quality to remain constant in its digital form throughout any subsequent compressions and de-compressions?
Sorry if this seems wordy, I’ve had dangerously little sleep in the past two days. (-:
Think of a MP3 file as a JPG compressed image, the first compression may look nice, but if you re-compress it again you´ll see some fuzzy edges and artifacts, do it again and it keeps getting worse.
MP3 is not a loseless compression format, you can´t get back the same quality as you started with.
Actually, it’s an easily perceptible loss in quality for all but the best MP3 encoders, and even the best MP3 encoders require ~200kbps to achieve “transparency” (when you can’t tell the difference between MP3 and CD Audio.)
Yes, except again, it’s not miniscule. The quality loss happens for pretty much the same reason it happens the first time: MP3 encoders are “lossless” and so are always throwing out information. The difference in bitrates is the difference in how much information the encoder is throwing out. Even the highest MP3 bitrate, 320kbps, is throwing out 1091kbps of CD audio (1411 - 320). This will happen every time, as MP3 cannot recreate the original perfectly.
As someone mentioned, the same thing happens with digital pictures. Try this simple experiment:
Get a digital photograph. Any digital photograph will do, but for best results it should be large (1024x728 or larger) and should also be fairly “busy”. A city skyline with lots of detail works well.
Using any photo editing software, shrink the photo down… a lot. At least to 1/2 size, but more is much better. I’d try reducing down by 80% just for kicks.
Save the picture.
Open “new” smaller picture in same editing software and increase the size to the original.
Look in shock and horror at how bad the image looks. Look at the general fuzziness and artifacting going on.
(OPTIONAL) Repeat the above process several times and see how progressively worse the picture gets.
Although the actual “guts” of photo compression and music compression are not the same - different algorithms are used, different techniques, etc. - the net effect of multiple JPEG or MP3 compressions is the same.
You can get lossless sound compression formats, but like with anything, there is a price.
They will usually only compress about 50-60%, so you save some space but nothing like as much as MP3.
The file format might not be well supported, or you will need to use plug-ins for you Music Player. This also means that they are not particularly attractive for distribution.
One example, Monkey Audio, does have plug ins to use on several rippers such as CDex and players like WinAmp and is one of the better supported formats.
Lossless formats are probably of more interest to home studios musicians and maybe those who are restoring rare archival work, but if you have some rare vinyl or wax you would rip initially to a lossless format, but uncompress it to wave file to work on it with some program like CDart.
Yes. Burning it to a CD will do nothing, quality-wise. When you burn it to a CD, the information that was thrown away during the compression isn’t replaced; once it’s gone, it’s gone.
Once an uncompressed original source file - be it audio, video, or an image - is compressed using a lossy format, you CANNOT get back to the original quality. Multiple compressions will just further degrade the quality, each throwing away more and more of the data. It’s like making a photocopy of a photocopy - each subsequent compression will get you farther and farther from the original.
What I’m thinking is that maybe when you burn an mp3 file as audio to a CD. Maybe the audio that is comes from an mp3 source is somehow easier to compress back into mp3 again.
I tried making a JPG picture smaller and bigger again. The first time I lost a lot of quality. But when I did it 4 more times the loss of quality was a lot less than the first time.
You WILL lose quality. How much quality, I don’t know. I would guess the graph of bits lost to number of compressions isn’t linear and depends greatly on the source material.
But once those bits are gone, they’re gone, and uncompressing a lossy compressed file won’t get them back.