What's the deal with CD players being used as transports?

Discussion in 'Playback Devices' started by NicholasL, Sep 25, 2004.

  1. NicholasL

    NicholasL Second Unit

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    From my understanding, CD players/multichangers can be used 1 of 2 ways.

    1) As a transport.

    2) As a player utilizing it's own internal DAC's.

    As such, this basically means that by using digital interconnects (optical or coaxial) between the CD player and the receiver/preamp, the CD player is thus qualified as a "transport." If, on the other hand, the CD player is connected via analog interconnects (RCA or XLR), then you will be utlizing the CD's own internal DAC's.

    This being true, and I don't know if it is, but wouldn't that mean no matter what level a CD player is ($60-$25,000), connecting it with a digital cable would make it all sound the same, since all signal processing would be taken charge of by the receiver/preamp? Becaues if that's the case, why would ANYONE with a high-end CD player use it as a transport? Wouldn't they simply be better off using the CD player's own, internal circuitry to produce sound?

    And along these same lines, wouldn't that mean any DVD player, SACD player, or DVD-A player connected with a digital cable produce the same results? Identical sound compared to another player connected to the same receiver/preamp??

    I am really quite confused on this subject, and if someone can shed a little light on it I'd be much obliged.
     
  2. ScottCHI

    ScottCHI Screenwriter

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    it seems you actually DO have a fairly good understanding of this. basically, yes, a player connected digitally is acting only as a transport. of course, the quality of the transport mechanism does vary from manufacturer to manufacturer and player to player.

    THE GENERAL "RULE" IS THAT YOU DECODE WHERE YOUR BETTER DACs ARE. that rule, however, is superseded by the even more simple rule that "you decode where it sounds best to you". so, someone with a really high-end player might decode at their receiver/pre/pro if it has even higher quality DACs than their player. or, perhaps they just feel it sounds better decoded there.

    btw, unless one's equipment is equipped with an iLink or firewire connection (and most aren't), then sacd and dvda MUST be decoded at the player, and played back via a multichannel, analog connection.
     
  3. EricRWem

    EricRWem Screenwriter

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    Is it pretty easy to determine, via the literature for the player and the pre/pro, which one has the superior DACs?
     
  4. FeisalK

    FeisalK Screenwriter

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    it's also easy to test if you happen to have a cheapo DVD player and a reasonably better one - if what you say is true, they should sound the same through either digital interconnect.
     
  5. StephenL

    StephenL Second Unit

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    If you use your receiver's or processor's bass management it's generally better to use a digital connection from the player to avoid the extra Analog to Digital and Digital to Analog conversions.
     
  6. ScottCHI

    ScottCHI Screenwriter

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    no, it's not always clear.

    and sometimes, what sounds better to someone is NOT necessarily the "better" DAC.
     
  7. ChrisWiggles

    ChrisWiggles Producer

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    Subjective listening to compare dacs is the way. I feel my Marantz 5300 sounds better decoding the discs than my NAD521i cd player. This surprised me quite a bit actually.

    The original poster does understand things correctly, however it does not necessarily mean that all players used as transports will sound the same, since there absolutely are people who (real or not) differentiate between transports, etc. If you don't believe or hear differences in transports, than sure they'll all be the same. If you do, then maybe they'll be different.

    Stephen L also makes an excellent point. If you are using your CDP as a pplayer (using the player's dacs) you want to make sure you are in some sort of direct mode to avoid any A-D/ D-A conversion *again* in the receiver, as this is degrading.
     
  8. NicholasL

    NicholasL Second Unit

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    Scott, when you state that it depends on the quality of the transport in each player, what exactly constitutes a transport mechanism? Are they as distinct from other brands/players as their DAC's?

    To be more specifc, please allow me to list the two CD players I own, and why I have this question.

    I own a 400 disc Sony ES multichanger, the M333ES, and a single disc dedicated CD player, the Classe CDP-10, which is arriving in a week. The difference here is the megachanger retailed for about $500. The single disc player retailed for $2000...

    ...so I've been using the Sony with my Parasound C2 with a high quality toslink connection. I figured the DAC's in the pre/pro were superior to the megachanger's. However, when I try taking CD's out of the megachanger and playing them in my Denon 3800 DVD player, which is ALSO connected with an IDENTICAL toslink, they sound VERY different!

    Which then makes me scratch my head and ask myself whether I should be buying a high quality toslink for the Classe player arriving in a week, or a pair of XLR cables? Since it's apparent to me that 2 different "transports" can actually sound different. And yet I have no clue how the Classe's internal DAC's compare to the Parasound Halo C2's internal DAC's. AHHHHH?!?!?!
     
  9. ScottCHI

    ScottCHI Screenwriter

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    i didn't say anything really "depends" upon the quality of the transport (or did i?). i said that that differs from player to player and manufacturer to manufacturer.

    if there IS an audible difference in the "quality" of the sound from 2 players connected by identical digi connections, and all other explanations have been ruled out, then the difference must be due to their different "transports".

    however, even though you may indeed hear a difference in that situation, discerning which is the "better sound" can sometimes still be very difficult.
     
  10. Doug Otte

    Doug Otte Supporting Actor

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    Nicholas, I think the main difference in transports affects jitter. A cheaper transport doesn't spin the disc very precisely, e.g. the spinning could waver very slightly off-axis, like a spinning top, but less obvious. That could cause jitter in the signal that's read by the laser and thus transported to the DACs. A better transport supposedly spins the disc more true to its axis and thus the laser reads the data w/ less jitter.

    I could be completely wrong, and I'd be glad for more knowledgable folks to correct me. Or, there might be more to it than just jitter, so feel free to amend.

    Doug

    Edit: Oops. I should have looked at the HTF Glossary right here on this site. Here's the definition of jitter:

    "Jitter - The unwanted variations of a binary signal's leading and trailing edges. It occurs as the signal is processed or transmitted from one point to another. Most jitter is caused by noise picked up from a phase-locked loop (PLL) in the signal path. Jitter also is a time displacement, either periodic or random, of a signal's switching edges. You can think of jitter as the lengthening or shortening of one signal element, usually one bit time, in an NRZ binary signal. Jitter also can be considered as a form of FM, and it produces an FM-like spectrum."

    So, I guess a cheaper transport could introduce jitter, but I'm not sure how it's reduced on a better player. Again, please chime in if you know more.
     
  11. Chu Gai

    Chu Gai Lead Actor

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    Jitter only has meaning at the point of conversion and virtually all players, including the portable ones have comparatively neglible amounts. Neglible enough that its not audible by a couple of orders of magnitude. If you find out what model of DAC you have, you can look up the specs at the vendor's website. What you'll invariably find is that the DAC has incorporated within it, anti-jitter circuitry.
     
  12. Doug Otte

    Doug Otte Supporting Actor

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    Thanks for clarifying, Chu. So, to repeat Nicholas' question, what aspect of the transport can affect quality, and how is it different in better machines?

    Thanks.
    Doug
     
  13. Chu Gai

    Chu Gai Lead Actor

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    Personally, I don't see the transport being an issue unless the DAC itself has issues. I'll talk more about it later. Hold on to your money in the meantime.
     
  14. NicholasL

    NicholasL Second Unit

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    Well my Classe CDP-10 player arrived today, but it's just sitting pretty in the brown box right now, as I have to wait for the rest of my "upgrade" gear (PS Audio P1000 Power Plant, 15amp Ultimate Outlet, 3 PS Audio power cables, a 250ft spool of Z1-series monster cable, 2 15ft lengths of Z2-series monster cable, a center channel 10ft length of Z2-series monster cable, all the appropriate banana plug terminations, and a pair of PS Audio XLR cables).

    SO!* Once all that crap arrives at the doorstep, I can finally take apart the whole system, and find out once and for all how different all my players (Sony ES 400 CD changer, Denon 3800, and JVC multiregion DVD player) sound as transports, and then how they sound utilizing their own internal DAC's.* So I will find out the how's.* But the why's are still yet to be determined...
     
  15. Chu Gai

    Chu Gai Lead Actor

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    You might start by determining if they all have the same output voltage and if there are no channel imbalances. That could be done by burning a test tone and measuring the voltages at the speaker terminals with a VOM while leaving everything else in your system the same. While the CD standard for maximum output is 2 volts, you'll find that is a standard that isn't adhered to all that closely. For example, the Arcam FMJ CD33's output is 2.22 volts. Your CDP-10's is 1.98 volts. I don't know what the other units you've got put out but I mention this because unless you level match at the very least, simple level differences will obscure any other difference assuming they're there.
     
  16. Lewis Besze

    Lewis Besze Producer

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    Chu,
    he's going to test them via digital links, so their respective analog stages are being bypassed.I've yet to encounter level differences among players using digital outputs,or sound quality differences.Though nothing is impossible.[​IMG]
     

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