CD audio: quality loss seen in copies?

[thereaderrabbit]

We're having a bit of a debate here in the office today about the following issue...

If I make a copy of a CD from an audio source CD to an image file, which is then burned to a CD-R, can I expect any discernable audio quality loss? How about from burner to burner or copies of copies?

I've been looking into this and can't find any official sources with an answer to this question.

My friend says that when he plays a copy loud in his car it's not as clear and lacks the volume of his original. I don't buy that, but I was wondering if there was more to it than I knew. Help?

-Reader

 

[borealiss]

if it's a true bit for bit copy there should be no difference.

 

[thereaderrabbit]

borealiss,

That's what I'm thinking too (since he's been using Nero and all), but I still would like to hear from more people on this.

-Reader

PS. I also miss Calvin and Hobbs dearly, but can't afford to keep buying more books

 

[blahblah99]

Shouldn't be any errors, especially if error checking is employed. The only reason I can think of is his copied CD may degrade over time, hence the extra noise.

 

[Mark R]

Digital errors are usually not subtle (clicks or pops). Changes in 'quality' or 'volume' are not characteristic of digital errors due to generational loss.

There is always potential for read errors with any system - but CD audio is less reliable than many digital systems today. For example, HDDs are might be designed for 99.9999999999999% accuracy, CD-ROMs might be designed for 99.9999999999% accuracy, but audio CDs may only be 99.9999999% (These are not accurate figures). Because of audio CDs lower reliability, under adverse conditions (e.g. dirty CD) there may be multiple errors on a copied disc (even if the disc appears to read correctly).

There is a concept called 'jitter' which could affect the quality of the sound from a CD-player. Essentially, on a CD the data is recorded in a serial format. This digital stream of data is then transferred into a digital-analogue converter. Essential to the operation of the DAC is an accurate clock, which ensures that the analogue waveform is reconstructed very accurately in both amplitude and time (both of which affect the sound). It is concievable that inaccurately placed marks on the disc, could affect the timing of signals entering the DAC, leading to inaccurate sound - and this may have been an issue with old CD-players. Although, at first sight, this seems an attractive theory there are a couple of problems:

1) Modern players, have a buffer and re-timing mechanisms to ensure that the DAC clock is near perfect.
2) Modern CD-R drives and discs can often exhibit lower jitter than mass-produced 'pressed' CDs.

 

[KalTorak]

All that assumes it's a bit-for-bit copy.
If, for instance, the CD copying software decided to re-normalize the audio levels, it might sound quieter or louder... and if the data got compressed and uncompressed for some reason, then all bets are off.

But yeah - a bit-for-bit copy that's the same pulse-code-modulated WAV? There is no difference.

 

[thereaderrabbit]

Thanks you all for the info! This was what I was kind of thinking, minus all the quality details

 

[AMB]

http://www.whathifi.com/newsMainTemplate.asp?storyID=29&newssectionID=3

Similar idea mentioned there

 

[glugglug]

Some CD readers do not allow digital audio extraction, so the sound actually gets resampled by your sound card resulting in quality loss. These drives are generally really old though, and any CD copying software and drive from the last 5+ years should support DAE.

Even with DAE though, CD-audio tracks, unlike data tracks, do not have any bits used for parity/error checking, it is all used for audio samples. So it is possible , although unlikely, for there to be read errors which result in clicks. This is unlikely at least when reading with a recorder because your drive's write error rate is likely to be as high or higher than the read error rate, and if they were at all common you would be burning a lot of coasters.