Hi

I know that this is a Home Cinema forum, and my question falls more in the Hi-Fi category, but I'm sure there are a few of you out there, who has a decent Hi-Fi system as well and may have given some thought to the following problem, which I have recently spent quite some time thinking about. And the topic is relevant for DVD users as well, so I think I can defend to post it here.

Making a digital copy of a CD should in principle create a perfect copy (e.g. in a dual deck CD-Recorder where the signal is never converted to analog). Several people/magazines/companies suggest that this is not the case:
- "The XXX CD-Recorder makes near-perfect digital copies". Why only "near-perfect"?
- "XXX Recordable audio discs gives significantly better quality copies than YYY". Why?
- "A digital copy created at 4Xspeed is not as good as one created at normal speed". Why?

So how come, that digital copies are not always perfect. Even if a few bits here and there were toggled on the copy, the error correction should be able to handle the situation (even a small hole in a CD can be corrected by the CD error correction on most players...) so why is it that it doesn't work like this in practice?

Any comments are welcome, but I hope I don't start a very long thread like discussions about cables etc. Next topic from me will be why digital interconnect cables sound different, but I'll wait a bit with that... ;-)

/Allan

Allan, in my opinion, a digital-to-digital copy should be an identical clone of the original, which is why the SCMS was developed. You can copy an original, but you can't copy a copy.

As far as media differences go, I could imagine that a high number of drop-outs could exceed a players ability to interpolate midding data, which could lead to an audible difference.

It's also possible that a high-speed digital copying process causes data losses, which results in distortion sounding like excess-compression artifacts.

In short, unless proven otherwise (to me), a digital-to-digital copy will not be discernible from the original. From the reviews I remember reading, digital copies are identical.

Larry
www.fineelectricco.com

Larry,

I've made quite a few CD compilations by ripping songs from my commercial CDs and combining them onto a CD-R. I have no idea why, but the sound quality does suffer. It's still very good, but you can most definitely hear the difference.

I'd sure like to hear the explaination if we can find someone who knows...

LarryTN:

When ripping, the software has to be carefully configured for optimal quality. The default settings on virtually every ripping software I've encoutered are optimized to compress the signal, giving you more songs per disc at the expense of reduced quality.

I've been told the software manufacturers assume that most ripping is done by "Walkman" users, who can't notice the degraded signal when listening through walkman-style ear buds and headsets.

When I rip an audio CD -- whether to WAV or MP3 or simply copying the Redbook file -- with the software set for top audio quality and no compression, I can't tell the difference between the source or the copy even when played back through my best speakers or headphones. Of course, my EARS aren't the greatest in the world... :)

greve, this also applies to your original post. Just one person's opinion, but I've never noticed media or recording speed to make an audible difference in a copy. The only exception is when the speed was so high that the buffer overran and the entire recording attempt failed (toss that disc and try again). When it works, it has always sounded the same to me.

As pointed out above, there is a big difference between a 1:1 digital copy of a CD and "ripping" (i.e. load the music into a computer and then let some software convert the PCM signal music to e.g. MP3 signal music).

I'm talking about the potentially "purest" form of copying being the 1:1 direct copy of a music CD onto an Audio CD-R in a (Hi-Fi) CD Recorder.

I would sure appreciate more opinions on the topic. In the meantime I have provided a few links to reviews where "expert" Hi-Fi reviewers have mentioned that such copies are not perfect.

Test of various Audio CD-Rs and (Hi-Fi) CD Recorders:
[Link: hifichoice.co.uk]

Quote from test of TDK CD-RXG:
"From the opening bars of the first test track, the ability of CD-RXG to provide inherently smooth-sounding, richly detailed copies was obvious. Unusually, the analogue tape hiss audible on the (original) CD of Carmen Lundy's Better Days was seemingly less obvious on the TDK copy without denting the resolution and spontaneity of the percussive hi-hat. Intriguingly, our digital dubs sounded uniformly warmer and smoother than the original without appearing detrimental to the performance itself."
Full review on [Link: hifichoice.co.uk]

Quote from test of Philips CDR951:
"Recordings retained the qualities of the original discs from which they were made when played back through the Philips, and sounded very close even through the more analytical Krell test player."
Full review on [Link: hifichoice.co.uk]

/Allan


This message was edited by greve on 01/13/02 06:24.07.