Direct Digital output

Discussion in 'Beginners, General Questions' started by Chaminda, Mar 9, 2004.

  1. Chaminda

    Chaminda Auditioning

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    Hi All

    I hope someone can clarify this... I plan to purchase a Universal DVD player that I will also use to listen to CDs with. Advise I read from "What HiFi" stated that when listening to music it is better to switch the reciever to a channel using the coaxial cables rather than use the digital cable. The reason being is that apparently from the disc the digital data is converted to analogue via a DAC and then back to digital via a ADC within the player, prior to being piped to the reciever which then processes the digital data before reconverting to analogue via DAC for each of the channels. With each step there will inevitably be data loss and noise introduction

    However via coaxial there is only a single DA conversion in the player. But why such a complex pathway via digital? The DACs in my reciever are already pretty good (most likely better than in most DVD players) and I was wondering if anyone new of DVD players that output the digital signal directly, allowing for just a single DA convertion at the reciever end. This should give higher fidelity for music and films.

    I eagerly await your replies. And please use layman terms as I wouldn't class myself as a raving enthusiast just yet.
     
  2. Ted Lee

    Ted Lee Lead Actor

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    maybe i'm misunderstanding you, but there isn't different DA conversion depending on the type of cable being used - at least i don't think there is.

    the question you need to ask is whether your dvd player or the receiver does the better conversion. generally (but not always) the receiver does the better job.

    so, if you want the receiver to do the converting, use the digital connection. if you want the dvd player to do the converting, use the analog connections.
     
  3. Vince Maskeeper

    Vince Maskeeper Producer

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    You should provide a link to what you were reading, as in most cases "coaxial" and "digital" cables are the same thing. Saying you should use coax rather than digital is like saying you should take the Chevy rather than the car.

    This above thing you outlined is true, essentially, for using the analog connection on a player (D/A conversion in the player, A/D in the the receiver back to D/A for amplifier output)... where using a digital connection limits things to one D/A stage (in theory)... however I think the terminology here might be confused.

    -Vince
     
  4. Ted Lee

    Ted Lee Lead Actor

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    hey vince ... you've been elevated back to those oh-so-lofty heights???
     
  5. Chaminda

    Chaminda Auditioning

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    Sorry for the terminology confusion. When I say coax, I mean the original definition as follows: "A type of wire that consists of a center wire surrounded by insulation and then a grounded shield of braided wire. The shield minimizes electrical and radio frequency interference.
    Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks, such as Ethernet. Although more expensive than standard telephone wire, it is much less susceptible to interference and can carry much more data."
    Digital cable on the other hand is just a fiber optic link..It is this that I have an issue with.

    Using the "analogue connection" is only a single D/A conversion in the player as the amp can then bypass all circuitry to give a "source direct" signal. However most digital connections from DVD players do DAC then ADC, within the player, and the reciever then has to do DAC again. I would rather get a DVD player which I know outputs a pure digital direct signal to the digital connection so that only a single DAC occurs in the reciever.
     
  6. ChrisWiggles

    ChrisWiggles Producer

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    Whoa this is a VERY confused post/thread:

    There are three connection methods that I see as your options:

    1) Analog. This is two coax RCA cables that transmit the analog audio that has been converted from digital to analog int he player. What happens later is a separate issue, see later in this post.

    2) Digital. Two options:
    a) Coax Digital. Uses a single 75ohm coax to transmit the digital stream to an external decoder, usually a receiver.
    b) Optical digital. Uses an optical cable to transmit the same thing to an external decoder.

    Your use of "coax" thus is ambiguous because you could be talking about analog stereo, or digital (SPDIF) transmission over coax cable(s).

    The method you use will vary depending on the quality of the DACs in your receiver, and in your player.

    If you use an analog connection, the audio is decoded in the player, and sent to your receiver. What your receiver does with it varies on your setup. Using a S-direct type option will leave the signal in analog usually, and output it directly full range to your mains, and sometimes also full-range to a subwoofer. However, you can also often utilize bass management on analog inputs, whereby your receiver does ADC conversion, applies BM digitally, then DAC conversion again. This is something you'd probably want to avoid.

    If you use the digital connection(either coax or optical), your receiver does the all the decoding. Again, you'd still probably want to refrain from using BM, unless your speaker's lack of bass capability demands it. I suggest you try each connection method, and use whichever sounds best.

    In my setup, I find that my CD player and receiver are very close, however, I prefer the sound of the DACs in my receiver, so I use a digital connection. Everything stays in S-Direct regardless, for stereo listening.

    I hope that makes sense?
     
  7. Vince Maskeeper

    Vince Maskeeper Producer

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    No- most will not process internally in any way- it reads a direct digital stram off the disc and passes it. There is no additional D/A A/D stage in any of the players I ahve dismantled, and I assume this would be true of the majority out there (there would be no need to).

    In which case it's a matter of who's DAC you're using (analog connections using the player DAC, digital connection using the preamp DAC).

    -Vince
     
  8. Chaminda

    Chaminda Auditioning

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    Right I understand the coax/digital terms now.. and this was my worry when posting on an enthusiast forum in that the conversation has diverged around the terminology rather than the issue itself.

    You say that using the digital optical cable, no DAC/ADC occurs in the player, but "What HiFi and Video", which started life as a HiFi audiofile magazine, strongly advise not to use a DVDs digital output when listening to music, because the player does not stream the digital data directly from the source and does DAC/ADC within the player and then the recieve does DAC again, all prior to reaching the speakers. They advise using the analogue connection meaning the player does DAC and thats just a single process step rather than 3 if using a digital link.

    I'm only looking at DVD players in the sub £500 ($800) range, which maybe below the level of the players you take apart. I can only assume that the digital path goes through the same DAC within the player regardless of whether you use digital or analogue connection and then only if using digital does it need ADC prior to output. Maybe higher end players have a dedicated digital path directly to the digital output connection. Obviosly if they all did this the advice would be to use the digital link for pure audio as well wouldn't it?
     
  9. Wayne A. Pflughaupt

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    Someone correct me if I’m wrong, but I think there is some kind of conversion for the optical digital output. Perhaps that’s what they were talking about. I don’t think it’s as drastic as a DA /AD conversion, though.

    Regards,
    Wayne A. Pflughaupt
     
  10. Vince Maskeeper

    Vince Maskeeper Producer

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    I don't understand why you would assume this. I can't see what the reasoning would be to convert something to analog until it was absolutely necessary...

    First off, why add an extra A/D converter? It isn't needed, and would serve only to potentially degrade the signal. A far simpler, and more cost effective solution would be to omit this stage, and only have one set of converters, for the analog output. I can't see much logic in paying for the extra step to undo what you already did- especially on cheap equipment.

    Secondly, you seem to make this assertion in conjunction with DVD players as the playback device. If this were the case- it would be fair to assume (if you're going to assume all you ahve in the first place) that ALL signals in the player would be handled as you suggested: Immediately converted to analog off the disc.

    However for multichannel soundtracks- this would be terribly counterproductive. Not only would it mean an extra A/D stage, it would mean at least SIX CHANNELS of converters just to undo the D/A stage you suggests it is performing.

    What's worse, once it's analog inside the player and needs to go back to digital- you'd need a different set of converters/encoders for material that started DTS to get it back to DTS. So if it followed this same "not really directly digital" method for everything, and I can't see why it wouldn't- it would have to keep track of the original encoding type, bitrate and meta-data, just so it could re-encode it back to the original format before passing it out as digital bitstream...

    Then don't get me started on players that support MPEG audio or MP3...

    So, essentially I think it's pretty basic to see that it is HIGHLY unlikely that a DVD player is twice converting DD or DTS signals, I would find it hard to believe it would bother doing so with PCM cd data (again, i can't see any logic if it can pass the digital stream of a DVD soundtrack directly, why it would jump through a half dozen extra circuitry loops that were redundant).

    If the player has the obvious ability to pass dd/dts streams directly without this unnecessary extra conversion stage, I'm not sure why it would be difficult to assume the same could readily be done on PCM cd data.

    -V
     
  11. ChrisWiggles

    ChrisWiggles Producer

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    No, the optical and digital coax transmit the same stream following the same SPDIF protocols, AFAIK. The only difference is one uses electrical signals, the other, light signals. I have a book on high-end audio, and the author claims to hear differences between the two, and references bandwidth specs and such that are higher for the coax transmission of SPDIF. Others also feel that the very cheap light emitters costing but a few cents, are a weakness and prefer the robustness of electronic connections the whole way, and not a electrical-light-electrical interface. This is not my opinion, I just thought that maybe this would be something that Wayne was getting at.

    As for any conversion going on in the DVD player, I don't know. You'd have to quote the what hifi article more in depth so we know what they are talking about. Some players do upsampling, perhaps they are talking about avoiding something like that, which I don't see why they would do that, or perhaps a DVD player does funny things with the 44.1 versus 48 for DD/DTS sampling? I am working on the assumption that it just spits out the PCM that's on the disc directly, as in a CD player/transport, but perhaps they were dealing with a player that does funny things? Perhaps...
     
  12. Chaminda

    Chaminda Auditioning

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    Yes Chris that makes sense. I can't quote the article as it was a while back but of course, the optical signal from the laser is converted to a electrical digital signal with in the player and then back to optical prior to the players output. The recievers would then have to reconvert the optical signal back to electrical... process the data and then do DAC for each of the channels before outputting to the speakers.

    Inevitably this would be noisier than the player converting the optical source data to electrical carrying out DAC prior to output, and the reciever then simply has to amplify that signal. Hence the recommendation not to use optical connection for the best sound quality.

    Thanks for clearing that up. So I guess my question should be are there any DVD players that output the optical signal from source with little or no electrical steps inbetween?
     
  13. Vince Maskeeper

    Vince Maskeeper Producer

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    But this is a digital conversion. I can't see how it would matter if you carried the ones and zeroes as light versus electrical signal. It's on and off- if you expressed is as electricity, light or even as a man waving flags- I can't see how you would claim it was being degraded.

    I could see if it was being changed into an ANALOG electrical signal, with thousands of variables- but we're talking about transmission of data.

    In fact, while I don't know for sure- I would assume the way coax digital signals are expressed in terms of digtial data is probably done differently than it is handled in the receiver (just like on a network- the actual ELECTRICAL pulses of a digital signal can be transmitted dozens of ways-- like Manchester, Differential Manchester, NRZ-L, NRZI, etc) - this is the same concept.

    I could see having a problem with the weak transmission of light, or with how noise could be intriduced into an optical signal- but to complain about the conversion from/to light and electricity seems a bit of a stretch to me.

    -V
     
  14. Chaminda

    Chaminda Auditioning

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    I don't know for sure, hence this thread, but there must be a reason why pure audiophiles strongly advise using the analogue connections rather than the optical.

    Though pure audiophiles will use dedicated audio source equipment. I just want to achieve the best musical sound I can from a home cinema setup (as I can't afford to buy seperate players for movies and music).

    I have a UK tuned Marantz 5300 which has a slight bias toward music over AV, and simply want to bring the best out of this reciever when listening to music (on a DVD player [ie CD, DVDA, SACD]). For me this has been a useful thread in understanding terminology and a bit about signal pathways, so thanks all for that. But I'm still a little uncertain as to which DVD player to get, or how to set it up for music.
     
  15. ChrisWiggles

    ChrisWiggles Producer

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    The thing is I don't think they are making that claim. I've heard them make the claim not to use OPTICAL as opposed to COAX digital, but whether there is any truth to that is irrelevant to me because coax is cheaper and easier to deal with so I use that everywhere anyway.

    There may be reasons not to use digital outputs to external DACs because of jitter and different clock issues, but IMO this is getting REALLY picky, and for more advanced setups than anyone who is using a DVD player for CD playback anwyay.

    I have a MArantz 5300, and an NAD521i CD Player, with dynaudio 52SE speakers, and I'm using radio shack fusion cable for both analog and digital connection. The move to the rat shack cable was quite an improvement over freebie cables. Regardless, I prefer using the digital connection in this setup because the marantz DAC's are more detailed (or perhaps my analog cable should be better, I will experiment with that sometime in the future). It won't cost you but a few minutes of your time to use both and decide which sounds best. The difference in my setup is not huge, and wouldn't be noticable to people unfamiliar with my system, but it is a subtle change in detail and space.
     
  16. ChrisWiggles

    ChrisWiggles Producer

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    Now, be clear though, that with DVD-A and SACD, to get high-res playback with an SACD/DVD-A player, you MUST use 6 analog cables. Because of copyright concerns there is no digital transmission of this data except for proprietary in-brand links, i such as some pioneer elite stuff, meridian, etc.
     
  17. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    Ahh, it was awhile back. I suspect you are remembering the point made in the article slightly wrong. They were probably warning about HT receivers that take a stereo analog signal and by default, digitize it to do bass management and other processing in the digital domain (DSP modes, midnight mode compression etc), then back to analog before amplifying for the speakers. This extra round trip occurs in HT receivers, not DVD players. As several have said, most decent (but not all) HT receivers allow you to defeat this by selecting "direct" analog inputs. Does this ring a bell ?
     
  18. Chaminda

    Chaminda Auditioning

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    ...err, no.. it was talking about DVD to AV reciever setup, in answer to a letter asking whether to use digital or analogue connection for listening to music.
     
  19. Vince Maskeeper

    Vince Maskeeper Producer

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    And what Brian said was directly related to that.

    Anyway- bottom line, don't listen to an insane esoteric nonsense- from that magazine or from me- just try it, and decide what YOU hear.
     
  20. Ted Lee

    Ted Lee Lead Actor

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    sheesh ... isn't that what i said like in the second post? heck, you could have saved yourself an inane amount of techno-babble... [​IMG]
     

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