Measurements Are Hard

Discussion in 'Measurement Techniques Discussion' started by purr1n, Sep 29, 2017.

  1. purr1n

    purr1n Finding his inner redneck

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    I don't even know where to start. A few days ago, someone pointed me to this post:

    http://www.superbestaudiofriends.or...purpose-advice-thread.19/page-263#post-163746
    I wrote an initial reply here: http://www.superbestaudiofriends.or...purpose-advice-thread.19/page-265#post-164614
    continued next post...
     
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  2. purr1n

    purr1n Finding his inner redneck

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  3. purr1n

    purr1n Finding his inner redneck

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    Or this of the Bifrost (assuming D-S):
    Schiit BIFROST.png

    Hahaha. I'm sorry, that's not jitter, that's measurement error, with a spur that high up.
     
    Last edited: Sep 29, 2017
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  4. purr1n

    purr1n Finding his inner redneck

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    BTW, here is my Modi 2 measurement for comparison:

    24-bit, 44.1kHz J-Test
    Modi2 Jitter.png

    Compare to the hack job below:
    [​IMG]

    MORAL OF THE STORY / LESSONS LEARNED:
    1. Measurements are a pain the in ass, and they are very easy to screw up.
    2. Having expensive gear like an AP doesn't mean it's any easier getting them right.
    3. Beware of rando measurements on the Internet.
     
    Last edited: Sep 29, 2017
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  5. schiit

    schiit SchiitHead

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    There's a reason I keep a set of IEMs around to plug into amp prototypes--sometimes saves me days of chasing down noise problems that aren't really noise problems, but are caused by a bad cable or ground between the device and analyzer. Sometimes. Other times, like last weekend, I burned two days on a prototype before remembering to plug them in. Yeah, I just burned two days for nothing.

    There's also a reason Mike and Dave look askance at Jtest and use interval analyzers to look at jitter on the word clock. There's also a reason we don't usually get into the graphs game, because the Stanfords have a couple of non-standard tests that aren't easily comparable with measurements not made on Stanfords.

    Bottom line: measurements are a good guide, but they are not always 100% accurate, nor are they always 100% meaningful.

    No idea what happened with the Modi with wonky measurements--we were never contacted by the reviewer, so I don't even know the provenance of the product.
     
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  6. atomicbob

    atomicbob dScope Yoda

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    Vetting the data from a measurement run is both time consuming and tedious. Often there is at least one or two measurements requiring a redo, even after the most meticulous session.
     
  7. purr1n

    purr1n Finding his inner redneck

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    I've always scratched my head on how you've been able to get such excellent and consistent results. I thought you might have been an immortal being or something. Glad to know that you've faced the same difficulties I've experienced. As I like to say: "It's a good night tonight for measurements!"
     
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  8. SineDave

    SineDave Friend

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    Audio in particular is a rough area in this regard because our measurements are so quickly scrutinized.

    I've been flummoxed for hours after taking several measurements of a speaker or sub, and the final measurement run is just off by a good 10%. Turns out the 9V battery in my mic preamp was starting to die, but this wasn't obvious until I'd exhausted tons of other options.

    It would be nice if we could convince AP to send you their top of the line meter @Marvey , especially when we measure some of the same gear JA of Stereophile measures, it would be nice to use the same kit.
     
  9. Torq

    Torq MOT: Headphone.com

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    Go to @atomicbob's house ... the ambient noise level is almost unnaturally quiet ... as-in ... you can pretty much hear Dr. Emmett shedding.

    In the other room.

    If his power-feed is that good too, well ... there you go.
     
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  10. atomicbob

    atomicbob dScope Yoda

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    Some nights require more than a good glass of red to de-stress; something along the lines of Macallan Rare Cask.
     
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  11. Torq

    Torq MOT: Headphone.com

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    I have a single, remaining, Maccallan ME that is in need of suitably learned company to properly enjoy ...
     
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  12. Armaegis

    Armaegis Friend

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    I believe 90% of the answer there is practice.
     
  13. Cspirou

    Cspirou They call me Sparky

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    Last edited: Sep 29, 2017
  14. atomicbob

    atomicbob dScope Yoda

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    A good way to practice is to measure the same device, same suite of measurements on different days. They should be very close. When one can do that frequently then confidence has been gained for both accuracy and repeatably.
     
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  15. atomicbob

    atomicbob dScope Yoda

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    That sounds like a plan.
     
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  16. purr1n

    purr1n Finding his inner redneck

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    LOL. I thought he was a 24 year old objectivist with an AP analyzer too good for his Kung Fu* - Audio and Science and all.

    *Kung Fu actually means skill or ability, derived through practice, discipline, or hard work. For example, the phrase "Your Kung Fu is no good!" can be applied as much to a carpenter as to a martial artist.
     
    Last edited: Sep 29, 2017
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  17. purr1n

    purr1n Finding his inner redneck

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    Indeed. @atomicbob's Kung Fu is very very good.
    PaiMeiPromo.jpg
     
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  18. Bill-P

    Bill-P Level 42 Mad Wizard

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    Yeah, Kung Fu technically means "high articulation" or "skills" or something like that, I think. Not the "martial arts" meaning tho back in the old days, martial arts were the only thing that people could practice, so Kung Fu would mean just that.

    I'd imagine many people in this community... if they were living in ancient China, would be badasses like the 108 vigilantes of Chinese lores.
     
  19. Xen

    Xen Friend

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    Aye, measurements are hard. That is why, when I was doing Science, months or even years were spent making a robust protocol that gave consistent results. Then you measured the thing you wanted in a week or two. Also, another reason why standards were developed and used so that anybody anywhere could have the same internal and external error controls when doing the measurements. Of course, publishing the protocol so that others could hopefully replicate your methods to get suitable close measurements.

    Let's not talk about recertifying if ANYTHING gets changed... (kid you not, manufacturing told research , where I was, that removing a paper clip early in the manufacturing process would take months to be approved...)
     
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  20. atomicbob

    atomicbob dScope Yoda

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    Thank-you all for the high praise and honors. I hope I am making a contribution, given the knowledge I have gained reading reports from dedicated listeners here. It is far more rewarding to listen to Schiit than shit, as one example.
     
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