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Digital audio basics

Discussion in 'Audio, Video & Home Theater' started by twilyth, Jun 20, 2011.

  1. twilyth Guest

    I learned a great deal in a recent trouble-shooting thread I had posted and I thought a lot of the information presented there was worth codifying so as to make it easily available to others interested in digital audio.

    Special thanks to streetfighter 2 and BumbleBee but also everyone who contributed including Sinzia, Jetster and hat.

    I'm probably going to overlook a lot of valuable information, not to mention making any number of errors, so I'm reserving a few slots for later additions and will edit posts as my errors are pointed out. Please post and indicate any information that should be included and I will either plagarize you post to include it the main sequence or edit it as necessary to keep it clean and easy to understand.

    HDMI is superior to analog and other forms of digital audio

    Even people who are tech savvy may not realize that the HDMI interface provides a far superior method of reproducing audio from digital sources. The audio functions are generally seen as a convenience which allows you to have a single cable for DVI video and digital audio. But in fact, it goes so far beyond that.

    HDMI can handle up to 8 24-bit channels with sample rates up to 192khz (or higher). It can also handle a variety of compression protocols, although the extent of it's capabilities are hardware dependent.

    This means that if you have a relatively recent discreet video card or IGP, you have everything you need to produce the best sound from any digital source.

    HDMI vs S/PDIF

    Most motherboards have the ability to output an S/PDIF signal, however, optical transfer of digital audio has numerous limitations. For example an S/PDIF connection can only handle 4 channels at a 44khz sample rate. And while it technically has 24-bit resolution, it is designed for only 20 bit.

    In addition, S/PDIF can't handle many of the protocols that HDMI can.
  2. twilyth Guest

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  5. streetfighter 2

    streetfighter 2 New Member

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    Mussels actually made a similar thread, though it doesn't get into much of the real technical grit:
    http://www.techpowerup.com/forums/showthread.php?t=141676
    Where'd you read that?

    SPDIF can handle DTS and AC3 just fine. It just can't do DTS-HD, Dolby TrueHD or anything more than 2 channels PCM/lossless.

    If you try to run DTS-HD or Dolby TrueHD thru SPDIF it should convert to DTS/Dolby core (aka compressed/encoded stream). I've tested this myself and I honestly can't tell the difference between master and encoded on my sound system, but it might just be the audio clip I'm using.

    In order to use DTS-HD and/or Dolby TrueHD with your HT and HTPC you need:
    1) a graphics card that can bitstream those formats (HD 5XXX +, GTX 460, GTX 5XX+, H67+, etc.)
    2) a couple HDMI 1.3+ cables
    3) a recent version of arcsoft or powerdvd (w/ HD bitstream)
    4) a DTS-HD or Dolby TrueHD source
    5) a compatible receiver
    6) a compatible display
    7) an HDCP compliant datapath (for bru-lays :D)

    It's so easy . . . :rolleyes:
    Optical or coaxial transfer of audio doesn't have limitations (as far as I know), but SPDIF does. The SPDIF protocol is old but the cables themselves, RCA coax and TOSLINK, have enough bandwidth to transfer DTS-HD and Dolby TrueHD. As I understand it, the only reason that DTS-HD and Dolby TrueHD aren't bitstreamed through a RCA coax or TOSLINK is because the SPDIF protocol does not provide HDCP.

    Kinda hard to get a good source here . . . This is the best I could do:
    SPDIF is the protocol. I think you're referring to the "format" (sometimes informally called a codec).
    Last edited: Jun 20, 2011
    Jetster says thanks.
  6. twilyth Guest

    This is why you got the gilded invitation with the fancy calligraphy dude. What? You think it's because I like you? :laugh: ;)

    So what are the limitations on S/PDIF? I know bit rate is one.

    Also, maybe you could decode this paragraph for us mere mortals since it doesn't sound good but that's the most I can get from it.

    Thanks again :toast: :respect:
  7. Thatguy New Member

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    I'll bet you a whole boatload of cash that you can't hear the difference between 16b 44.1khz and 24b 96khz and 24b 192khz.
  8. twilyth Guest

    I've done a couple of impromptu tests and I know I can tell the difference between some mp3's and flac. But honestly, I haven't really tried to find my limits. I think that most lossless formats sound better and I try to avoid the lower resolution stuff. I think a lot of that preference though is due to artifacts that I tend to notice in tracks that are aggressively compressed. I'm particularly sensitive to resonances that don't seem to be part of the music.

    The point though is, that if you want the best possible sound reproduction, HDMI is the way to go. And while so much in the realm of audio depends on what you're willing to pay, HDMI gives you the best reproduction for virtually no additional cost - whether you can appreciate the quality or not almost doesn't matter.
  9. Thatguy New Member

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    I will bet you large sums of money that you cannot here the difference in a proper listening enviroment.Using double blind methodolgys.
  10. streetfighter 2

    streetfighter 2 New Member

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    It won't do:
    • DTS-HD
    • Dolby TrueHD
    • PCM/lossless > 2 Channels
    Unfortunately I am also a mortal :laugh:.

    I think it's just saying that since the clock is propagated from the source and employs no error recovery mechanism then there is potential that a distorted clock signal could prevent the DAC from lossless reception. Also check out bit slip.

    The part about breaking TOSLINK cables is relevant to all fiber optic cables.
    HDMI is the way to go for HT nuts (like me). For audiophiles who are often more interested in stereo (and triode amps :shadedshu) then SPDIF and an outboard DAC may be the right choice. (source)

    Or you could skip the whole affair and buy a bloody studio sound card. (source)
    Audiophiles are some of the dumbest people I've met. Some of them believe in shit as retarded as bi-wiring. Also check this.
    Last edited: Jun 20, 2011
    Jack Doph says thanks.
  11. twilyth Guest

    OK, so most of the limits with s/pdif have to do with bandwidth in the sense of not being able to reproduce high bit rate? Is that a fair summary?

    So if you want to handle more than 2 channels at a high bitrate, either you use HDMI or analog outputs from a sound card?

    I'm just going to try to hit the basics so i'm going to gloss over the more technical topics.

    That was an interesting article about audiophile lies.
  12. Thatguy New Member

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    I have a nice little studio at my house. I am well aware, although I like the sound COLORing of analog gear.
  13. slyfox2151

    slyfox2151

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    no offence, but i really can tell the difference between 44100 and 96000 @ 16b.

    i have no way of proving this to you however, but there is a clear difference in sound.
    (i could not tell you witch sound was 44 or 96 in a double blind test, but i could tell you if it sounded different from the last test.)




    oh and HDMI is not ALWAYS Superior to analogue.... if you have shitty DACs it doesn't matter how the digital audio got there.










    if my receiver supported it, i would be running 4 analogue cables to it instead of HDMI, then i could buy and make use of a high end sound card with high quality DACs. not to mention upmixing / playback of 2.0 5.1 7.1 is a pain in the ass having to change the output settings in windows.

    my receiver wont support any upmixing if i set my sound card to 5.1 or 7.1 output even if only playing 2 channel audio sauce. playing a blu ray in 5.1/7.1 wont work if the sound card is set to 2 channel to allow for upmixing.
    (i dont upmix music i leave it play in stereo, but i have a lot of 2 channel movies i like to upmix.)
    Last edited: Jun 20, 2011
  14. seronx

    seronx

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    Wait, don't you mean ADCs?
    Analog->Digital Converters

    because going to

    Digital->Analog seems pretty lossless since digital streams as long as they are received properly can be decoded pretty well
    meaning
    Digital->Analog is not what you should be worrying about

    Everything played on the computer unless you can somehow rip Super Audio CDs
    is pretty much well 16bit aka Analog
  15. slyfox2151

    slyfox2151

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    OH?
    so what would be the need for a high end audio card then? i assume this uses DACs, the quality of witch would partly deter-men the level of audio quality.





    how is 16bit analogue? my understanding is its the total possible range of the dynamic level.
    Last edited: Jun 20, 2011
  16. Thatguy New Member

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    How much money are you willing to bet on this with a double blind listening test ?
  17. BumbleBee

    BumbleBee

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    yeah the winner gets to move in with this guy lol

    [​IMG]
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  18. Widjaja

    Widjaja

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    I can not hear the difference between 44.1 and 196 either.
    I Fired up Cakewalk Sonar 8.5 PE and ran some soft synth recordings.
    Absolutely identical in sound to my ear.
    Only difference to me was the file size.
  19. streetfighter 2

    streetfighter 2 New Member

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    You've got great questions but it's hurting my head trying to figure out how to answer them. :laugh:

    As I wrote in a previous (heavily edited) post, as far as I can tell, SPDIF's limitations are merely a failure to update the standard for use with multi-channel master audio. Furthermore there is little motivation for such an update because SPDIF is incapable of providing content protection (which HDMI does provide).
    Most modern receivers will ADC (and subsequently DAC) an analog input signal, rendering your high quality DAC ineffective anyway :ohwell:.
    I agree. Your audio performance is only as good as the weakest element in the audio chain.
    You can use ffdshow filters to upmix stereo to multi-channel (either using Dolby Pro Logic II or custom speaker matrix) and then have the processed signal bitstreamed to the receiver.
    I'll write about why this is inaccurate later . . . preferably after I get on a computer with MATLAB.
  20. Thatguy New Member

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    There are some mix time and mix down reasons to consider higher bandwidths and bit depths, more dynamic headroom, more smearing of samples, give the end mix a bit more breathing room in some ways. same way running the tape speed higher improves the noise floor of tape,


    but when it comes time to playback, I'll go grab my golden ear muffs and pretend away like th best of them.
  21. slyfox2151

    slyfox2151

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    i dont belive i need to bet money here. when i switch between 44 and 96 on either my old z-5500s i could tell there was some sort of difference between them.
    (using Optical)


    if i had to guess, i belive i noticed the effect most on higher frequencys.


    EDIT:
    doing the same test on my newer sony system, i cannot hear a difference...
  22. Thatguy New Member

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    You have your answer. Now if your dealing with massively complex music with lots of dynamic range and many channels, that bit depth can help to give more realism to audio effect in a surround system, but its the bit depth and not the sampel rate that gives those benefits, most people have trouble with discerning 2db changes in db levels. Most modern music on the radio today has less then 8bit of dynamic range.
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  23. Widjaja

    Widjaja

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  24. FordGT90Concept

    FordGT90Concept "I go fast!1!11!1!"

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    Klipsch disagrees with you. Hell, only Logitech and Apple have really embraced digital. Why? Because all speakers are analog because the human ear is analog. If you have a digital decoder in your computer that is superior to those found in receivers, TVs, etc. you're going to get a richer sound sending an analog signal to the speakers than you will a digital one.

    When it comes to audio, the only advantage of digital is fewer physical connections between the output device and the speakers. When it comes to actual sound quality, it depends on the quality of digital decoders and amplifiers.
    Crunching for Team TPU
  25. BumbleBee

    BumbleBee

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    I think it's a Teres Turntable and the one underneath with the yellow LED is a Soundsmith pre-amp.

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