DDC Measurements - Audio-GD DI-20HE, Pi2AES, ifi Zen Stream

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by GoldenOne, Jul 22, 2021.

  1. Gazny

    Gazny MOT: ETA Audio

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    it could improve, but many things are subjective
    I would attempt to utilize the spdif first.
     
  2. GoldenOne

    GoldenOne Friend

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    I'll be updating this post soon, as I now am able to measure the jitter of I2S directly.

    Why couldn't I do this before?
    The APx555 does not support LVDS I2S input, which is the connection most DDC's use. So you cannot analyze jitter directly in the same way that you can with SPDIF or AES using the advanced digital I/O module (which is how I've been evaluating DDC's thus far).

    You also can't just connect it to the analog inputs of the analyzer, because you can't look at a 28Mhz clock signal on an analyzer with a 1Mhz bandwidth.

    How do you get around this?
    A really ideal way, and the method L7 AudioLab uses, is to get a true NOS R2R DAC without an internal reclocking mechanism.
    The Holo Spring 3 is a true NOS DAC and the PLL can be disabled, so it works rather fantastically for this use case. And when you play a square wave at 1/4 the sampling frequency through it (J-Test), it is effectively acting as a 2048x clock divider. Outputting a 12Khz square wave (from a 48khz sample rate), and you can look at the jitter components on it via the analog inputs of the APx555

    https://www.l7audiolab.com/f/l7audiolab-the-magic-mirror-test/

    What are you going to do?
    I reached out to Jeff Zhu about this, as he is a metrologist, and has developed some products with pretty incredible clocking/jitter related performance such as the Holo May, so I thought he would be the best person to go to.
    Jeff was an absolute legend, and offered to design a clock divider board for me, which allows for an adjustable frequency division, and output of both the word clock and master clock.

    I now have it here, and it's working absolutely brilliantly.

    [​IMG]

    This means that I can take the I2S output of any DDC, and use this clock divider to analyze jitter with greater accuracy and lower noise than a DAC would possibly be able to provide.

    So we can look in incredible detail at the performance of a good DDC:

    upload_2022-8-30_13-50-53.png

    And a great DDC:

    upload_2022-8-30_13-51-13.png

    I don't have all the DDC's on the list here, but I'll make I2S testing the main focus going forward as it's the main way people will be connecting DDCs to their DACs.

    A HUGE thank you to Jeff Zhu for this.
    Only thing is I'm gonna need to look at getting an AUX-0025 or AUX-0040 filter because of the fact that the square wave bandwidth still exceeds the analyzer bandwidth, and so that could be negatively impacting things to some degree (See this PDF for more info on this, this is usually a concern when testing Class-D amps but its the same mechanics here) https://drive.google.com/file/d/1_zRhb1MYwHD1OJJgnjDiRtKZmd9EtnBD/view?usp=sharing
     

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    Last edited: Aug 30, 2022
  3. GoldenOne

    GoldenOne Friend

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    Also, this enables a pretty close look at the implied phase noise too!

    wK40ptsXDV.png QVv7TBeNme.png
     
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  4. Clemmaster

    Clemmaster Friend

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    This is fantastic!
    Do you still have the Wavedream NET? :D
     
  5. SoupRKnowva

    SoupRKnowva Official SBAF South Korean Ambassador

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    that embed of the unit wasn't working.

    [​IMG]
     

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