Time Distortion & Music at Today's Atlanta Audio Society Meeting

Discussion in 'Archived Threads 2001-2004' started by Lee Scoggins, Feb 16, 2003.

  1. Lee Scoggins

    Lee Scoggins Producer

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    For regular CD (redbook) and high resolution digital audio, audio signals consist of (1) musical data in the form of one and zeros like computer data - the Y axis and (2) time code not like computers - the X axis.

    Time code is the least understood. In 1992 some friends of mine and I worked on a Test CD for Chesky Records. We recorded some music with a digital interconnect between the ADC and the digital storage unit. We tried a very high jitter cable ($2) and a low jitter cable ($500). In preparation of a new audio test CD, I had an opportunity to conduct a blind test at the Atlanta Audio Society today.

    What happens when the time code is off just a little bit?

    Each music sample was exactly the same in musical data of a drum solo with increasing dynamics. Around 20 Society members were in attendance. We listened twice to each sample and no one was told which was the lower jitter sample. In this brief test, we found roughly five people felt that the first sample (high jitter) was more musical and around 15 preferred the lower jitter second sample. While not the last word in studies, this confirms our basic contention of the audibility of jitter.

    We have also noticed that when we add an external master clock to our beloved Alessis decks, the jitter goes down from 200 picoseconds (yes, that small!) to 20 picoseconds (ps) and the music, particularly strings opens up to more detail. The image seems tighter and more musical.

    We have discovered two scientific proofs of jitter. This is important for reproducing music since this time-based distortion

    The first is by Julian Dunn of Nanophon:

    http://www.nanophon.com/audio/jitter92.pdf

    See Section 3.3 Audibility of Jitter. Here Julian finds that 20 ps should be the threshold of audibility on high frequencies.

    The second paper is by Eric Benjamin and Benjamin Gannon presented in 1998 at the AES where audibility was discovered to 10 ns.

    What is the value of all of this for music fans?

    (1) Buy hardware that has lower jitter statistics. These can often be found in Stereophile and The Absolute Sound.

    (2) For the best in sonic realism, purchase music that is produced by audiophile labels that use low-jitter recording chains.

    This jitter also affects the production of the "glass master" used in the CD manufacture. I will comment on this in a later thread as I learn more of the details.

    Think of it this way..."bits are bits when they arrive at the precisely right moment in time."

    Do you have any experience with certain CD transports sounding better than others?

    Do you believe in jitter's audibility?

    Do you find Julian's paper to be valid?
     
  2. Michael St. Clair

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    Lee,

    How was the jitter introduced for today's test?

    Did the person playing the samples know which was which? Was this person visible to the listeners? Was there a control group? Were the listeners listening alone, or with the other listeners?

    Could the listeners listen to each sample as many times as they liked? Could they rapidly switch between the two?

    How were the listeners asked to report their results? On paper, raised hands, verbally, or something else?

    I think it has been well established that introduced jitter can, in at least some circumstances, create audible distortion. But whether a given blind test was valid depends on many things.
     
  3. Lee Scoggins

    Lee Scoggins Producer

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  4. TomCW

    TomCW Second Unit

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    Lee - not to be a pain, but how was the 'jitter' of the cables determined? Was test equipment used, or was cost the sole criteria?
    There are cables available for many $$$ that perform worse than some $2 cables. There is enough snake-oil in the audio cable business to grease the entire world (IMHO).
    Thanks for the info, it raises some interesting issues.
    Tom
     
  5. Lee Scoggins

    Lee Scoggins Producer

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  6. Justin Lane

    Justin Lane Cinematographer

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    What was the seating arrangement of the testers? Is their a corralation to seating location, to those who thought the high jitter sample sounded better?

    This is good for a preliminary test, but I think if I were to be scientific about the test, I would set up a listening room without any outside influences where it is just the listener and the high or low jitter track randomly switched.

    J
     
  7. LanceJ

    LanceJ Producer

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    What exactly is a "low jitter" cable?

    LJ
     
  8. Lee Scoggins

    Lee Scoggins Producer

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  9. Phil A

    Phil A Producer
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    Lee, what was the rest of the system set-up out of curiousity? Were the Espec's Activ? They sound much better and more revealing that way, although perhaps not as forgiving.
     
  10. Lee Scoggins

    Lee Scoggins Producer

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  11. Al B. C

    Al B. C Supporting Actor

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    Lee - was Niles Crane there?

    And also, what kind of wine and cheese were served? [​IMG]
     
  12. Phil A

    Phil A Producer
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    Lee - that is just Linn's terminology for biamping or triamping. Linn's amps come with the crossover built-in, without them you need an outboard unit. If the Linn speaker wire was used (they make multiple conductors in a black flat wire that is about 2 inches), which is typically how many dealers sell it, it is not necessarily the best choice for sound vs. convenience in one jacket. It is very easy to bi-wire with it, and it is fairly reasonable, but not the best sounding. I was just curious as to speakers, amps, source components, etc.
     
  13. Lee Scoggins

    Lee Scoggins Producer

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  14. Phil A

    Phil A Producer
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    The preamp is very good. The Klimax amps (I think $9,500 each are good but when they are driven for more than a brief period at high levels (I think they are 270W in 8 and 500 into 4) have a fairly audible fan noise, a trade off for the nice looks and small package they come in.
     
  15. Lee Scoggins

    Lee Scoggins Producer

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    I was very impressed with the CD12 CD player but $20K is out of my reach! [​IMG]

    Talk about build quality - metal drawer and solid cas of aluminum for the enclosure. Sweet!

    I bet this with the amps and the top of the line speakers sounds wonderful.

    [​IMG]
     
  16. Phil A

    Phil A Producer
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    One of these years while the local dealer has a CD-12, I may take it home just to compare it to the modded XA-777ES which is wonderful. In a few weeks, I have to take the preamp out for a software upgrade and also going to see how the XA-777ES works as a transport with my Micromega DAC and make a long digital cable . A guy up the road has the ($3.5k) Ikemi player and that would be a fun and easy comparison as well. Right now I have (Proceed) PMDT (which weighs about 40 lbs.) hooked up to the DAC as a transport and it is not too shabby either. I'm not much of a fan of the Komri's at $40k for the pair. They come with an amp built in and you need at least one other amp to drive them. They have them hooked up with a pair of the Linn mono amps ($19k/pair) at the local store and while it certainly produces good sound, I could think of lots things I would rather have for $59k or $40k if I had the cash. I was not much of a fan of the prior model either, the Celtic, although it was about half the price. It makes sense to go Linn if one wants to go that upgrade path. The Especs don't sound all that good next to speakers in its price range ($3.5k), but going active makes it a totally different animal and that is why I asked. I've helped install about a half dozen pairs, including a couple of active set-ups and there is no comparison between passive and active. Until I heard it active, I could not understand why someone would opt to spend $3.5k vs. looking at other alternatives.
     
  17. Lee Scoggins

    Lee Scoggins Producer

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  18. Joe Cole

    Joe Cole Second Unit

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    Phil,

    Have you posted a review of your modified xa777ES yet?
     
  19. Phil A

    Phil A Producer
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    Joe, no - at this point it is probably just about broken in and I am still trying things with it. I can tell you this, it has taken the unit to a whole other level on SACD. I've put on discs I have not played in a bit and am totally amazed at the level of transparancy. It definitely sounds better on redbook as well and I will listen more, but at least with minimal comparisons at this point I still don't think touches my PMDT/Micromega DuoPro DAC combination for CDs, which does not surprise me as I've heard very few things that do. I just made a longer digital cable for someone and I want to try the XA-777ES as a transport with the DAC as well on CDs. It would be very interesting if you could brink over the stock unit at some point and we could compare the units. From initial shipment until the time I got it back it was about 2 mos. even. I have the Elite DV-47A which I lived with for the 2 mos. which is not horrible but not great either for SACD. I actually got the DAC from a friend who was trying to sell it during the time it was gone since I was really missing the XA-777ES and wanted to really try it with a great transport like the PMDT. So in a way it was good as I would not have done that if the unit was with me the whole time.
     

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