Would I be losing SQ when I burn songs from iTunes onto a CD?
Nov 7, 2007 at 4:36 AM Thread Starter Post #1 of 27

Xoen

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I know iTunes isn't the best place to get songs since most songs are encoded at AAC 128kbps format, but I don't know of other places where you can get songs encoded at 320kbps formats.

Anyways, would I be losing SQ when I burn my purchased songs onto a CD at 1x speed?

One guy from another forum supposedly told me that I would be severly degrading SQ when I burn CDs.
 
Nov 7, 2007 at 4:44 AM Post #2 of 27

Trippytiger

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Data is data. Barring any errors in the burning process, I can't imagine that there should be any changes in sound quality when burning a CD.
 
Nov 7, 2007 at 4:57 AM Post #3 of 27

Xoen

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So burning a CD from iTunes or any other place shouldn't degrade the SQ in any way? I've always wondered about this. I don't normally carry portable media players around since I'm all for a home setup, but when I want certain songs and want to make a whole compilation of them, I want to be able to burn them onto a CD without worries of SQ degradation.
 
Nov 7, 2007 at 5:18 AM Post #4 of 27

K2Grey

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It should not. When you burn to a CD, the aac files are converted back to WAV, and then the WAV files are burned to the CD. So going from your iTunes files to the CD, there is no loss.

However, if you want to then rip from the CD, that will be a WAV->aac conversion and you will lose SQ.
 
Nov 7, 2007 at 6:03 AM Post #5 of 27

Singapura

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I've ripped most of my CD's in FLAC which doesn't degrade the sound. Unfortunately iTunes doesn't recognise FLAC so for my iPod I reconvert in Apple Lossless (I don't like Rockbox). When you convert back your result depends on the quality of your file (compressed or not) but I can imagine that the quality of the decoder counts as well. For quick conversions (for instance burning a CD for my car) I still use iTunes.
 
Nov 7, 2007 at 9:28 AM Post #6 of 27

milkpowder

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Quote:

Originally Posted by Singapura /img/forum/go_quote.gif
I've ripped most of my CD's in FLAC which doesn't degrade the sound. Unfortunately iTunes doesn't recognise FLAC so for my iPod I reconvert in Apple Lossless (I don't like Rockbox). When you convert back your result depends on the quality of your file (compressed or not) but I can imagine that the quality of the decoder counts as well. For quick conversions (for instance burning a CD for my car) I still use iTunes.


The CD will sound the same or if anything, marginally worse than the original lossy files due to misreads subsequently leading to error correction. Whether you can hear the misreads is another matter. Generally speaking, the bits on the CD will be the same as the bits of the lossy file so in an ideal CD transport feeding the same digital-analogue conversion circuit, they will sound the same.

Ripping the CD back to lossy files is not a good idea because the data on your CD already is a lossy copy of the original CD. Ripping into lossy again would result in further approximation. The resulting files are an approximation of an approximation of the original PCM stream. Again, whether the difference is audible depends on gear and ears.
 
Nov 7, 2007 at 6:03 PM Post #8 of 27

jilgiljongiljing

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Quote:

The lossy file will probably sound almost identical (if not identical) to the original WAV file. The second WAV file will sound noticably lower quality than either of the first two files.


I dont see how converting an mp3/aac to an audio CD/Wav will reduce the SQ. When the "gaps" are filled and the mp3 sounds "almost identical", wont it be filled with empty bits? Are you saying the upconverter tries to guess the type of music and fill data by itself?

No, it will sound identical to the mp3/aac.
 
Nov 7, 2007 at 6:09 PM Post #9 of 27

Xoen

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Oh ok, I pretty much understand now. I only burn my AAC files directly onto the CD without upconverting anything. I appreciate the replies!
 
Nov 7, 2007 at 6:17 PM Post #10 of 27

evilking

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Quote:

Originally Posted by fordgtlover /img/forum/go_quote.gif
The issue isn't burning it to a CD. Burning your existing AAC file onto a CD will have no effect on the SQ. However, if you mean that you want to convert your AAC file to WAV files and burn them to a CD so you can play them in a normal CD player, then the answer is that the SQ of the upconversion from AAC to WAV will result in a file with a poorer SQ than the original 128K AAC file.

The reason for this is that lossy compression removes part of the file (hence lossy). When you upconvert it the converter has to try to fill in those gaps as best it can.

Anyone can try this for themselves by simply taking a WAV files convert it to lossy file (MP3, AAC etc) and then convert the lossy file back to a WAV file.

The lossy file will probably sound almost identical (if not identical) to the original WAV file. The second WAV file will sound noticably lower quality than either of the first two files.




There is not a single true statement in this quote. Absolute non-sense.



EK
 
Nov 7, 2007 at 7:26 PM Post #11 of 27

milkpowder

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Quote:

Originally Posted by jilgiljongiljing /img/forum/go_quote.gif
I dont see how converting an mp3/aac to an audio CD/Wav will reduce the SQ. When the "gaps" are filled and the mp3 sounds "almost identical", wont it be filled with empty bits? Are you saying the upconverter tries to guess the type of music and fill data by itself?

No, it will sound identical to the mp3/aac.



I tend to agree with you. However, I am only using my fairly limited layman's knowledge.

First of all, WAV uses PCM (most of the time). Everytime you play a lossy file, a decoder turns the compressed data back to PCM before being sent to the DAC. The resulting analogue waveform travels down your pretty 9N audiophile-approved cables to the amp and eventually to your speakers/headphones. Similarly, whenever you rip an audio CD from lossy files, the decoder will turn the compressed audio data into a PCM signal that complies with the red book spec (16bit/44.1kHz). Hence, the resulting PCM signal is no different on the CD than if you were to create a WAV or AIFF file out of the decoded data.

Again, the only limiting factors I can think of that might make the WAV file sound better than the CD is 1. jitter introduced by the CD drive; 2. misreads by the laser, inherent physical inconsistencies on CD media resulting in audibly insatisfactory error correction or no correction at all (some errors non-correctable eg C2)

I am not the final word on this matter. Please someone enlighten us with corrections and the right answers if I have gotten something wrong.
 
Nov 7, 2007 at 8:13 PM Post #12 of 27

wanderman

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no loss is sq if your burn the files to cd as data or as wav(cda) files. The only way to can have a loss in sq is if you transcode using a lossy encoder. If your were to turn your aac to (mp4,mp3,m4a,ogg,mpc,or wma) you would have a loss in quality. If any of your transcoding steps involve a lossy encoder you will have a loss in quality.
 
Nov 7, 2007 at 9:37 PM Post #13 of 27

fordgtlover

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Quote:

Originally Posted by evilking /img/forum/go_quote.gif
There is not a single true statement in this quote. Absolute non-sense.
EK



Well, please explain yourself then evilking. If this is all you are going to say - you're just thread crapping. Please enlighten us all then.


Are you suggesting that buring AAC files to a CD decreases their SQ in some magical way? Are you suggesting that WAV to AAC is not lossy? Where does the upconverter get the information to add back in to create the original WAV file to enure it's the same as the original?



As I previously stated - try it for yourselves and make your own mind up.
 
Nov 7, 2007 at 9:57 PM Post #14 of 27

K2Grey

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WAV to AAC is lossy. AAC to WAV is not. You need to uncompress the AAC before you can play it for obvious reasons.

Edit: Another way to say it is that AAC is a compressed file. Before you can make sense of what music is in the AAC file, you must blow it back up to WAV (because it would be damn hard to read the file while it's in compressed form). The resulting WAV file is not going to be the same as the original WAV. But the point at which you lose information is the WAV->AAC conversion, not AAC->WAV conversion.
 
Nov 7, 2007 at 10:11 PM Post #15 of 27

milkpowder

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Quote:

Originally Posted by fordgtlover /img/forum/go_quote.gif
Well, please explain yourself then evilking. If this is all you are going to say - you're just thread crapping. Please enlighten us all then.


Are you suggesting that buring AAC files to a CD decreases their SQ in some magical way? Are you suggesting that WAV to AAC is not lossy? Where does the upconverter get the information to add back in to create the original WAV file to enure it's the same as the original?



As I previously stated - try it for yourselves and make your own mind up.



I don't understand where the "upconversion" occurs. Does anyone know how AAC is decoded? Is it decoded straight to PCM or are there intermediate stages? Encoding involves performing MDCT directly onto the incoming PCM stream, so is it fair to say that decoding is the same? In which case, there is no loss from AAC to PCM on CD.

Anyhow, I've reached the limit of my knowledge. I shall hold my tongue and listen
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