orginal or copy

Ian

The way a computer CD rom drive is designed is different from an audio CD player the firmware is different (hence the problem with copy protected CDs). Most of the cheap CD ROM drives are designed to accurately reading data disks Audio CD is a secondary function. Since data CDS have many more error correction bits than audio the drive can be designed very cheaply since errors are easy to detect and correct, if errors are not corrected then a flag is sent to the OS and the sector re-read hense no problem. with an Audio CD then firmware often does not tell the OS about uncorrected errors so these are accepted, by the OS.

It's easy to see why they are designed this way. When a CD ROM drive retails for less than a tenner and audio is classed as a secondary function to most users there is little money to invest in getting the audio error free. Lets face it most PC users (that don't frequent here) will be playing there CD's through five pound computer speakers anyway.

Chris

 

Yes Chris, but increasingly: (a) your domestic audio cd recorder; and (b) your audiophile cd player, will be using exactly the same kind of budget CD-ROM drive as your PC does.

The fact remains that if a disk->disk digital copy of a non-copy protected CD made on a PC verifies correctly it will be identical to the original CD. There's no room for argument about that, unless the burning software is broken in some quite fundamental way. Whether or not CD-Rs sound different to commercial CDs because of differences between media or production methods is a different question. Jitter (which is a product of playback) and data loss (which is a product of analogue copying) are completely irrelevent to the question of digital copying.

-- Ian

 

Ian.

The point is that most coppied audio CDs aren't done as a bit for bit copy. Most software that comes with the OS reads the audio CD just as if was playing it and relies on the drive to do the error correction, If the written disk is verified it is only compared to the data on the PC so if the orriginal read was corrupt so will the copy be. Hense the need to buy good ripping SW if you are going the jukebox/squeeze box route.

Chris

 

If the copy is identical to the original then the only difference can be the CD reading process.

CD's do not get 100% of the data off a CD. If they did why would there be need for error correction?

I stand by my statement that the reason the two CD's sound different is different parts of each CD are easier to read.

 

So that they can get 100% of the data off the CD accurately. If a CD drive (hardware) couldn't do that then it would be as good as useless to use with computers where even a single incorrect bit can make the difference between a document being readble or not. As Ian pointed out, many audio CDPs these days use computer CD drives. Unless you have a horrendously scratched CD any drive will be able to read 100% of the data/music on it 100% accurately.

Michael.

 

a) When any external effect causes data loss/corruption - eg Power and noise glitches, shock, vibration.

Copying music does copy bit for bit - no data is lost.

SOME players may lose info and not care ONLY when PLAYING. Consider playback as a 'time important' stream of data - the priority is time when reading AV data so error correction is slackened accordingly.

The only plausible reason for a copy to sound different would be the shape of the info bits stored on the copy and the servo tracking of CDRs (ie the media's propensity to track correctly).

 

This could be related to CDRs having different servo tracking capability to mass pressed media.

 

Error correction isn't 'slackened' exactly - as I understand it, the error correction is always running and all the data read by the transport passes through the error-correction stages (the notion of the error correction 'working harder' under some circumstances is yet another myth AFAIK). CD-ROMs drives do, however, have the additional luxury of being able to re-read data as an extra layer of error control, because as you note the time issue isn't so critical.

 

The data side of CD copying probably does stay 100% accurate or as near as. However, once the datastream is converted into laser pulses then loads of other factors - kenetic, optical, chemical, thermal, timing (and not to forget dust/fibre particles on the disc surface and read/write laser) come into place and thats where I reckon any 'changes/errors' would come into effect. Not that they necessarily make much, if any difference.

 

lAmBoY is right

 

According to Marantz (I'm referring to the audio cd recorder) the transport of the data stream induces a transformation from optical energy (laser) into electrical energy (print board) within the (source) CDP and the other way round within the audio recorder. Along with the correction applied within the source (which correction doesn't imply recovery of the damaged source, but rather a smoothening/softening caused by the imperfections), these transformations affect the '100% bit for bit identically' of the copy, ending up in a lesser accurate percentage as the bumps do not simply travel from one disc to another.

Absorption quality of the blanks is also a discerning factor. If it's easier to look through a blank disc when hold against the light then the copy will prove less listenable.

 

the cynic in me says that a dedicated audio cd recorder will purpously not make perfect copies. however a pc based ripper using software like EAC which is purpously designed to get the data perfectly will do just that.

this has got me thinking. does anyone know if there are any free pc programmes that will add dither to a wav? i'd like to experiment a bit.

cheers


julian.

 

Good point.

The Marantz "explanation" sounds like marketing voodoo to me.

-- Ian

 

Then I probably paid to much for the unit.