External DAC upsampling?

Discussion in 'Archived Threads 2001-2004' started by BobH, Apr 6, 2002.

  1. BobH

    BobH Stunt Coordinator

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    A friend and industry player has recommended that I upgrade a DVD player and then put an external digital-to-analog converter (DAC) between the digital output of the player and the analog input of my processor/preamp. This is supposed to improve the sound of all my CDs as well as DVDs by upsampling at a higher bit rate and frequency (BelCanto2 has 24bit/192kHz).

    1. How does a source like an 18bit/48kHz CD get improved just by running through a higher performance DAC?

    2. Would the external DAC at 24/192 be noticeably better than using the DAC at 24/48 in my processor?

    The main question is whether the source limits the output. The claim of my friend is that normal 20bit CDs through this 24/192 DAC sound as good as SACDs played on SACD players. Possible technically?
     
  2. ThomasW

    ThomasW Cinematographer

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    Bob

    The source doesn't limit the output, unless it's technically inferior (which the Bel Canto certainly isn't). The benefits of outboard converters are well known and very well publicized. But the only way to tell if the DAC you want is superior to the built-in ones, is via an in home audition. So try before you buy...
     
  3. Selden Ball

    Selden Ball Second Unit

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    Bob,
    A minor quibble: stereo audio CDs are only 16 bits sampled at 44.1KHz without compression. The HDCD format plays some trickery with the low order bits to get the equivalent of 20 bits. Multichannel DTS "CDs" nominally provide 20 bits sampled at 48KHz, but they have to use "psychoacoustic compression" to fit all the data into the same bitrate as normal CDs.
    External DACs can improve the sound by oversampling and interpolation, as well as by pushing the noise of the sampling frequency (and the resulting aliasing) up to much higher frequencies, where they're easily flitered out.
    You'll have to make your own comparisons to find out if an external DAC makes a real difference in your own system. Don't forget to compare it to all of the possible modes -- the player's analog outputs, both redigitized and "analog direct" through your existing receiver/pre-pro; as well as the digital output of your player through the digital circuits of your receiver/pre-pro, whether in surround-sound mode or "stereo direct".
    You should also try to audition the same titles on both SACD and CD, if possible. You may be surprised. In either direction [​IMG]
     
  4. BobH

    BobH Stunt Coordinator

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    Thanks guys. So upsampling is KNOWN to improve the sound of existing CDs. (any references?)

    Sorry for the typo, I meant 16bit not 18bit. Selden, were you saying that the "20bit" re-releases by such as Sony and Decca are not re-recorded from the masters, but "tricked" up? I assume they are not the same as HDCD because those say they are produced at 24bits. A little confusing.

    So what is all the hoopla about SACD and DVDA? I understand that RECORDED high bit and frequency is ideal, but if one can upsample existing recordings to 24/96 or even 24/192 with existing consumer equipment, why would SACD and DVDA be worth the (probably) small incremental improvement to most consumers?
     
  5. Selden Ball

    Selden Ball Second Unit

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    Bob,

    Upsampling can't provide what isn't there. It is not at all obvious that the upsampled interpolation recreates the same sounds that were present in the original recordings. That doesn't mean that it doesn't sound good, just that it isn't an accurate reproduction of the original music.

    External DACs are also supposed to include much better clocks and phase-locked loop circuitry. This improves the timings of the individual audio samples. Apparently some people can notice differences due to this effect.

    SACD and DVD-A formats are supposed to be able to provide a more accurate representation of the original music, if done properly.

    Also, from what I've read, most consumer grade 24bit DACs really aren't accurate in their lowest bits. Current technology just isn't up to doing that yet at reasonable prices. Supposedly 20bits or so is about the best currently available. Whether or not they used appropriately accurate ADCs and clocking in the recording studio is another question.
     
  6. BobH

    BobH Stunt Coordinator

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    Thanks Selden, as you said, the test is whether you can hear the improvement that you hope to make and it is worth the money invested. By the way again, what is the story with the re-released 20bit recordings (question above)?

    One advantage of SACD and DVDA is multichannel sound which I am definitely looking forward to. My processor doesn't have six analog inputs so I am hoping for someone to put out an ADC box in the future. No hurry, I expect this format war to last a while since few recordings are being done from scratch yet.
     
  7. Selden Ball

    Selden Ball Second Unit

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    Bob,
    One discussion of the advantages of oversampling can be found at http://www.earlevel.com/Digital20Aud...rsampling.html
    The new 20bit releases are another way to separate you from your money [​IMG] The discs themselves still contain only 16bit data, but since the recordings were made with the equivalent of 20bits of precision or better, they supposedly have a significantly lower noise floor. However, the results are mixed. See http://www.rogernichols.com/EQ/EQ_93-04.html
    If you like multichannel sound, there are quite a few DTS music "CDs" already available. Many Dolby Digital DVDs have quite respectable sound, too. And there are 24/96 stereo PCM DVDs (sometimes called DADs -- digital audio discs). All are compatible with non-DVD-A players. Although it was part of the original DVD-V standard, only a few models of players will actually pass the 24/96 stereo PCM bitstream. They do all provide analog output for those discs, however.
     
  8. BobH

    BobH Stunt Coordinator

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    Ah, more reading, thanks.

    Let me give you some examples:

    1. Sony Classical lists some new releases of old recordings as "mastered using 20-bit technology for 'high definition sound'. On the case are "High Definition Remastering" and "Super Bit Mastering." These same recordings have also been released as two-channel SACD. - Since these are remastered from the original tapes wouldn't they be legitimate 20bit recordings?

    2. Decca has some old recordings that are "Remastered at 96kHz in 24-bit digital stereo from the original analogue mastertapes." "Super Digital Transfer". Are these legitimate?

    You say some players will pass higher bit rate and frequency on, but how does one know? One of my Pioneers listed "24/96" on the case but nothing in the manual. My Panasonic lists only "96kHz sampling" in the manual. It would seem crucial to pick a unit that had the maximum specs for output to my pro or a DAC.

    I do have some of the dts and Dolby multichannel discs. I even bought a couple of DVDAs which have DD5.1 mixes. Some of them have very tantalizing mixes that give me the idea of what surround can achieve. In time.
     
  9. Dennis B

    Dennis B Stunt Coordinator

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  10. BobH

    BobH Stunt Coordinator

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    Interesting sites and good information.

    Are there any others that are more recent? The current crop of recordings don't help the confusion. There is HDCD which is disappearing but claims 24/96 which is the same as DVDA. Some DVDA discs don't list any specs, some say 24/96 but I haven't seen any at 24/192. Of course I haven't seen any players that claim 24/192 either.

    So just what does "DVDA" promise in frequency? At least SACD is consistent but I think it will lose. Myself and Joe-6-Pack can read the DD5.1 on the DVDA until we upgrade and then we'll have backward compatible systems.
     
  11. Selden Ball

    Selden Ball Second Unit

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    Dennis,
    Thanks for the correction. My finger must have twitched while doing the cut-and-paste.
    Bob,
    I was primarily refering to the problems of transfering 20bit audio reordings to the 16bit format, not to SACD or DVD-A. Optimistically, the latter formats will tend to maintain the signal quality.
    Riiiight.
    Sorry for the sarcasm. Quality obviously will vary from one title to the next. Maintaining the extremly low noise and larger dynamic range that's possible with those formats is going to be extremely difficult. Not all recording studios can afford the equipment and continuing calibrations that are going to be needed. Even so, I'm sure the average quality will be better than the average quality of 16bit CDs.
    As for the 24/96 PCM format indications, some players and pre/pros are quite clear about it. For example, my Pioneer DVD player (an F727 changer) and Marantz pre/pro (AV9000) both include that capability. The Pioneer's internal setup menu includes the option of downconverting 24/96 or of passing it unchanged. The pre/pro has a front panel indicator that lights up when a 24/96 bitstream is being decoded. The pre/pro's manual also points out that it can't apply any DSP funstions to that kind of signal, not even bass management. Only "stereo direct" is available. I have a few 24/96 DAD discs and they do cause the indicator to light up.
    I have to admit that I have neither a SACD nor a DVD-A player. I really can't get excited about either format yet. I guess my tastes in music are a little too plebian [​IMG]
     
  12. BobH

    BobH Stunt Coordinator

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    Plebian or not, you've been helpful. I may be slow but I am getting the point I think.

    Like you (and most folks?) I already have a library of 16bit recordings. If I understand so far, upsampling with a good clock and good filters should actually improve the sound of 16bit (and 20bit) recordings by reducing noise floor and jitter. I have already been surprised at the improvement resulting from putting my player on a Vibrapod sandwich (cheap too). I think you and the articles have answered my original question, thanks. So buying a player and/or DAC with better upsampling SHOULD sound better.

    What happens with SACD and DVDA is anybody's guess. Lack of interest in higher quality may be their bane. I am not sure if the general public will take to surround music. If they get it for free because of their home theaters, maybe. I am definitely a fan after trying DVDA discs (in DD5.1) of Vivaldi and Greatful Dead.
     

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