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who knows the truth of CD digital out?

Discussion in 'Hi-Fi Stereo Systems & Separates' started by jhkanguk, Sep 6, 2005.

  1. jhkanguk

    jhkanguk
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    I have a very fundamental question regarding digital output (optical or coaxial) of CD player.

    If same CD is played from £50 CD player and from £2,000 CD player, will their digital output different?

    If I am going to use only digital output, is there a point spending 2,000 on a CD player? (shouldn't I spend the money for better AV receiver?)

    What is the format of data on audio CD? (ie sampling rate and size).
    Is it same for digital output of CD player? If not, what format is it?

    Please can someone who knows definite answer help me.
     
  2. Nic Rhodes

    Nic Rhodes
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    The ouput is different, the 0s and 1s are the same. Cost isn't the issue, quality of engieering is and this is harder to quantify. There are some great cheap players that are good transports.

    More money on receiver, less on player? Try and see.

    CD is 16 bit, 44.1Khz
     
  3. Timbo21

    Timbo21
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    There are much more experienced & knowledgeable hifi enthusiasts on here than myself, but from my experience working with audio hard disk workstations I can tell you digital word clocks can make a huge difference to the sound both in image wise as well as effecting the whole frequency range. Additionally bad error correction can effect sound, so if there perhaps is a bad cd transport which is hindering the lazer picking up info on disk? Other aspects like power supplies & other components, but I really know nothing about this side of things. So, it's not all about DAC's, but you can greatly improve sound with a good outboard DAC.

    You need to balance CD player/amp budget. I think most on here would advise
    you using stereo amp for best quality replay of CD rather than a reciever. But if you want a reciever for both surround & stereo then it might be worth posting
    what level of reciever you are looking at & ask for advice on what to match it with.
    Arcam AVR250/300 for about £1000/£1300 are meant to be good stereo recievers
    also. But would you want to pair with a standalone CD player or DVD player which will play CD's also?

    CD is 44.1khz & 16bits. This is what will be output from digital o/p's of cd player.
    The size of data on CD? I think CDR's (recordable CD's) come in 700mb sizes, I think. Obviously each CD will be different, but I gues max will be about 700mb if my memory serves me right :rolleyes: .

    Hope this has helped. Someone else might be able to elaborate more :)
     
  4. jhkanguk

    jhkanguk
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    Thanks for replies.

    Your replies helped me come up with a clearer question.

    Which of below is true for 'digital data on audio CD' to 'digital data on optical out port' mapping?

    1. Digital data is read from audio CD and passed to optical out port as is without any processing.

    2. Digital data is read from audio CD and digitally processed for better sound and sent out to optical out port. No DAC/ADC used.

    3. Digital data is read from audio CD and converted to analogue by using DAC and processed and converted back to digital by ADC and sent out to optical out port.

    Thanks a lot.
     
  5. stevos

    stevos
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    1 & 2 are both correct

    The 0 and 1's are read and then passed through the error correction circuits. As error correction is not a extact science, it could be considered as processing. At no time is the data converted to analogue.
     
  6. Knightshade

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    Very likely, as already stated much here will depend on well matched quality components. However when used purely as transports i've found it pretty much impossible to tell the difference between my £100 DVD player and a £1000 CDP.

    Old adage here, garbage in, garbage out. It still holds true to a degree though the differences are becoming less apparent. Spending huge sums on CDP's isn't as necessary these days. I would be inclined to put more money into the AV receiver. But, if I were to spend £2000 on a Transport I would probably spend closer to £6000 on an AV receiver. I really don't think the AV route for 2 channel stereo is the right way to go though.
     
  7. severnsource

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    Error correction in CD players is an exact science. The way that data is laid out on the disc and the additional error checking data allow the original data to be reconstructed with no errors for large amounts of data loss. When too much data is missing then error concealment is used, which is variable in quality, but then perhaps discs that are that bad should be replaced!

    A lot of digital processing is done to the signal coming off the laser, but it is done to turn the unstable, encoded data stream into a clean, stable simple data stream for the DACs. No processing is done to change the sound quality on the digital outputs.

    There is very little potential for differences in sound quality between transports, and if you use a good reclocking DAC there will be no real differences - there is no mechanism for differences to be created.

    It would also seem that cheap players can have better digital output quality in terms of jitter than expensive players.
     
  8. Nic Rhodes

    Nic Rhodes
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    I wrote a huge thread here on this years ago but can't find it now :( Lost several other biggies as well.
     
  9. stevos

    stevos
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  10. CJROSS

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    Stevos I would point out that they make a huge difference or even any difference at all for some people. Some like me cant hear any difference between them in the DACs they have used (MF X-24K & DAC 20). In fact even with a 40 spec of jitter DVD transport into the TAG I felt it sounded identical to the last transport I used.

    I think transport issues with DACs are changing as many users adopt “new” ideas about transports and DACs, I draw peoples attention to Soundstream PC devices (Roku et al) with use with DACs, simple basic (as basic as you can get DAC technology) like the NOS DACs with very basic jitter recovering circuits.

    So transports make a huge difference for some audiophiles, not all.
     
  11. dynamic turtle

    dynamic turtle
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    I love hearing stuff like this:

    But then someone has to come along and spoil it by saying stuff like this:


    :D

    DT
     
  12. stevos

    stevos
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    The quality of the other electronics also make a huge difference, without good speakers there is no point in having a great cdplayer.

    I played around with my Cyrus cdplayer adding a psx-r and couldn't hear a difference, then i changed my speakers to some GR20's and was amazed at the difference the psx-r made.
     
  13. Knightshade

    Knightshade
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    Very valid point there. Balance is the key. Getting components that compliment each other is truely the key.
     
  14. hinesle

    hinesle
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    Just a little point – PC CD Rom drives are far more sensitive at detecting errors on media than any CD transport (that’s how copy protection works) and these drives cost about £20. What’s the point to this you ask? Well would it not be advised to simply RIP all your CDS with a program such as ECA to a PC (to get an exact copy bit for bit of the CD) and then play them using either the PC (with a decent sound card with digital out) or stream then to a device such as a Squeeze box Or ROKU with a digital out then using a decent DAC to decode it.
     
  15. severnsource

    severnsource
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    Sorry, but this does not correlate with all the explanations that I have seen about error correction in CD players. The data is converted from the very unstable amplitude varying raw form off the CD before error correction is applied. Audio CD data is encoded by a scheme known as Reed-Solomon coding, which was chosen because of it's ability to detect and correct burst errors. According to the Wikipedia entry on Reed-Solomon codes:

    "The result is a CIRC that can completely correct error bursts up to 4000 bits, or about 2.5 mm on the disc surface. This code is so strong that most CD playback errors are almost certainly caused by tracking errors that cause the laser to jump track, not by uncorrectable error bursts." - which correlates with everything reliable that I have read on the subject.

    What this means is that most errors occuring on an audio CD can be completely corrected; there is no approximation, no "about 80%". The reconstruction of the data is complete.

    Of course, if the disc is severely damaged, or is a very poor pressing then the error correction cannot cope and error concealment comes into play. This is approximate and can cause audible effects, but, as I said earlier, in the context of a high quality system such discs should be discarded.

    The quality of the laser pickup mechanism will have some influence over the quality of data recovered from the disc before error correction, but all that means is that a good mechanism will be able to play a poorer disc than a poor mechanism. On reasonable discs both will produce the same output bitstream. In terms of up-market CD transports this is academic, as the boutique manufacturers buy in their transport mechanisms from the mass makers anyway.

    Incidentally, I wouldn't bother to write any error correction formulae. The error correction formula for CD was set in stone by Philips/Sony before 1982.
     
  16. stevos

    stevos
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    Error correction was not set in stone, each maker uses there own additonal error checks. The redbook standard is great in theory, but since most cd's and players now a days don't fully comply by it, additional error correction is required.

    In theory you should be able to get a knife and cut through 2/3 of the disc and still be able to get enough information off it to reproduce the information perfectly. However with the use of 'enhanced' discs and 80mins discs, poor pressing, poor chemicals, smudge marks, etc things never quite work to theory.

    A PC drive can read the data 20+ times (i think, but this might be 10+, can't remember that far back) to ensure it gets the information correct, whilst a cdplayer can't.

    Either that or the likes of Meridian / Cyrus / Arcam / Denon etc that talk about their additional error correction codes on their tech guides must be telling lies.
     
  17. Timbo21

    Timbo21
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    A guy I used to work with told me a story of when Philips were first doing demos
    of CD & claimed it would withstand a hole being drilled through the disk! :eek:
    During the demo it apparently worked after drilling this hole!

    What they didn't show people was the cupboard sized computer under the desk
    which was doing the error correction :rotfl:

    Naughty Philips :nono:
     
  18. severnsource

    severnsource
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    Presumably you are talking about those CD publishers who choose not to observe the redbook standard in a vain attempt to copy protect their discs. AIUI these systems work by changing the way the data is written to disc and actually make use of the error correction system in order to render the discs playable. They were designed to be playable by bog standard redbook compliant machines, using the bog standard CD error correction system. Any CD player that does not comply with the redbook standard will not be able to play standard compliant CDs.

    If you are talking about the mechanism for recovering the raw data from the disc, before error correction is applied you may be right, but that isn't error correction it's just making sure the data is as good quality as possible before error correction is applied.

    I don't know where you get the cutting through 2/3 of a disc from or what it means. A good player should be able to cope with 1-2 mm sequential of loss of data on 1 track. The error correction system was designed to accomodate less than perfect pressings as well as small amounts of dust and damage to the CD and it does this perfectly well. In my experience the standard of pressing has gone up since the early days of CD.

    That is generally true, but irrelevant to the question of error correction. Multiple reads should improve the raw data quality so the error correction has better data to work on.

    Sorry I don't know of any such references, if you would like to give some references I would be interested to read them, although my suspicions would be that they were due to the marketing departments.

    CD makers cannot unilaterally change the error correction system. The error correction data is part of the data on the CD and that is not within the ability of the player manufacturers to change.
     
  19. stevos

    stevos
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    2/3 of the disk came from the original tomorrow's world program where Phillips showed off their new system. They got a stanley knife and cut a groove through 2/3 of the disk. I also say that drill test as well.

    The CD never did quite live up to this amount of abuse. Really wish it would though, as the number of disks i have that jump because of too many scratches (really old discs).
     
  20. jhkanguk

    jhkanguk
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    I am very impressed with so many comments!
    Here is what I understand now.

    If I use
    CD player digital output -> AV receiver
    the price of CD player doesn't make (noticeable) difference in quality of sound I hear.

    If I use
    CD player analog output -> Amplifier
    every components make difference.

    I know what to do now. Thanks!
     
  21. stevos

    stevos
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    jhkanguk that pretty much sums it up.

    Don't forget AV amps are not very good at CD reply, whether it is feed digitally or via analog.
     

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