Settle an argument !!

[daredevil]

Can anyone answer this question me and a friend are in debate about,

When you copy a dvd do you lose quality, I think the only time you lose quality is when you write to a cheap media or mess about with the file, My view is that when you take 1 digital source and place it on another of the same quality you lose nothing.

So with this argument a copy of a copy is just as good as the original......

Any views on this matter :sly:

[CooperS]

I remember reading on some reputable audio websites about losing a small amount of audio quality when making copies of copies over time - it never made sense to me because it is digital information. I'm not sure if the same thing applies to DVD's. I doubt it though.

[mg262]

Most commercial DVDs are DVD9s (~8.7GB); most backup media are DVD5s (~4.4GB). So something has to go... quality or extras or both.

[Joe Fenton]

With digital media, if you copy the files AS-IS with NO CHANGES, no quality is lost. Period. That said, as mg262 pointed out, most DVD backup programs have to shrink the DVD to fit the single layer media in most cases (it's rare to see single layer DVDs anymore). Shrinking can be done by tossing out 'unneeded' things like previews, extras, subtitles, and alternate sound tracks. If that doesn't allow the movie to fit on a single layer DVDR unchanged, quality WILL be lost. Now if you backup the dual layer DVD to a dual layer DVDR, then you have no loss again.

[MvB]

With the copying of audio cds you normally introduce jitter, with is responsible for different sound characteristics while playing in CD-players. But you'll have always the exact same digital information with every copy of the CD. The different sounding errors are produced on the way to the DA converter when the clock of your CD player isn't exactly synchronized to the data flow from the cd.

If you have a great cd player with an very exact crystal clock generator and an puffering memory where it reads the data from it's possible that your copy sounds exactly the same as the original in this particulary player.

Especially the newer plextor burners have a feature that's called gigarec, first introduced as 'audio master' by yamaha, that make the pits and lands longer, significantly reducing jitter while burning. Disadvantage: you loose space on the cd.

Not the same with dvd. You should loose nothing with an 1:1 copy (without recompression)
if i'm not mistaken, there is a complicated decoding process for audio and video where everything concerning time base, clock etc. is synchronized by the decoder and played in the right timeframe. But i have to admit i'm not an expert on dvds. if anyone knows better, please talk.

Cu
MvB

[shevegen]

Digital copying per se is lossless.

[Shinigami-Sama]

only way you'll lose is with read/write errors, unles you recompres it like someone said

[markrb]

If the copy is perfect and a true 1:1 then no quality will be lost.
Having said that though there will always be some read/write errors.
Most can be caught and fixed on the fly by the hardware, software, etc..,
but some very few make it through. If you are writting to another DVD then
no copy is ever perfect. Just take a look at any scans of burned DVD's at
cdfreaks. Will they be noticable to human eyes? In most cases no, but
it cannot be said that the copy is of perfect quality.

So your question really depends on how technical you want to get.
You will most likely not be able to see a difference, but technically
with current hardware it can't be perfect.

Mark

[mg262]

@markrb:
Would you happen to have any idea how often that goes past the error correction to translate into an actual flipped bit in the data on a burnt DVD? I know that this is a slightly imprecise question, since it depends on the burner and the media and how much time has elapsed -- so say for good quality (consumer) burner and media immediately after the burn?

[markrb]

I am really not sure.
There are others that know more then I do.
At cdfreaks they really know their hardware and DVD burners much better then I do.
I don't really understand Jitter, PIF/PIE errors and that stuff let alone even higher end.
I just am able to grasp the basic concept. I have never seen a scan that didn't have at least some errors in it.
My main point was that it cannot be a Perfect copy, with current hardware.
I wish I knew more.

Mark

[Joe Fenton]

Perfect copies are easy. For CDs, turn jitter correction on, and as long as the scratches aren't so bad that the error correction can't correct the errors, it'll read perfectly. Then after writing the disc, test it with something like Nero Speed Disc surface analysis. If it tests good, you have a PERFECT copy. For DVDs, just copy it directly (assuming it doesn't have the new 'bad sector' copy protection). Test it with Nero Speed Disc again. If it passes, you again have a perfect copy.

[Mug Funky]

jitter on media is usually a nonissue. it often gets confused with jitter inherent to the D/A converter, but they are not the same thing - if your CD player has a digital output you can transfer it to your computer and compare with a secure ripped wav off the CD. there may be fleeting differences depending on your CD player's EDC, but i doubt a modern CD player will have a problem.

as for copying DVDs, the only loss is from recompression. a 1:1 copy will be bit-identical so long as your media/playback equipment isn't completely incompetent (like a samsung standalone playing back a DVD-R burnt on a Sony drive for instance...). DVD has far safer error detection/correction than audio CD (audio discs were never really meant to carry data).

btw, DVD-5's are no longer seen much because the price difference between pressing 9's and 5's is almost negligible, especially in smaller print runs (10-20 cents more per disc for a 9?).

[daredevil]

Looks like I was right with my veiw then.. !!

he's now come back at me with this point,

if you take a picture with a digital camera and print it off, then take a picture of the picture you have just printed, when that picture is printed it will not be of the same quality as the first picture printed although its the same picture and a digital device is used,

my reply to that was, its because the original source has changed and that all prints from the first source will be the same as will all prints from the second source, (assuming each print out is the same quality) but there will be diffrences between the 2 sources.

Hope this makes sence and hope someone else can convince him of his errors.

[mg262]

Paper/ink is effectively an analogue format... so by printing you are applying a digital to analogue conversion.

[Neo Neko]

Paper/ink is effectively an analogue format... so by printing you are applying a digital to analogue conversion.

Yep ink is indeed analog. A better analogy would be to display an image on screen. Do a screen capture. Then compare the capture to the original. Technically you are going digital to digital there. At least at the point where the screen capture would take place which is before it actually goes to your display be it analog or digital.