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Thread: Audible Jitter/amirm vs Ethan Winer

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  1. #20
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    Quote Originally Posted by amirm View Post
    Beyond noise, you don't know if what you heard was true to the original. It could have been super distorted and you wouldn't know it. The only way to make sure you are linear down to the last bit is to measure it.
    I'm sure it was super distorted! A sine wave that occupies just the lowest one or two bits is by definition totally distorted.

    I don't know why you keep mentioning 100db. I have explained why that is not the right way to look at this.
    All I have to go on is the graph I showed from Ken Pohlmann's book, repeated here for your convenience:



    There's also one from John Watkinson's Art of Digital Audio, attached below.

    Let's review what the paper said:

    "It was shown that the detection threshold for random jitter was several hundreds ns for well-trained listeners under their preferable listening conditions."

    Now let's look at the AP graph I posted which was for a periodic jitter of just 7 nanoseconds, not "several hundreds" mentioned in the article:
    If anything that confirms my point, that even when not way down at -100 dB, such artifacts are still not audible. I got the lower than -100 dB figure from Pohlman's graphs. I do understand the difference between individual components that soft, versus the sum of all components which is of course much louder. So I probably should have been clearer when I said the artifacts from jitter are 100+ dB down.

    In practice, 60 or 70 dB is soft enough for artifacts to be inaudible even under the most favorable conditions. When I tested this I made a recording of a 100 Hz tone at nearly full scale, then added a 3 KHz sine wave that pulsed on and off at various levels below the music. These two frequencies are far enough part that masking is not a factor, and 3 KHz is where our ears are most sensitive. So this was a worst-case test favoring audibility. When the 3 KHz sine wave was 40 dB below the 100 Hz tone I could hear it start and stop. At 60 dB below the 100 Hz tone I could just barely hear it with the playback very loud. At -80 I could not hear it at any playback level.

    So even in your AP example of jitter sidebands at -80, it makes sense to me that nobody could hear it. Especially at those high and nearby frequencies. Indeed, in the example for my AES video where I played that nasty noise below a gentle passage in my cello concerto, once the noise was 40 dB softer than the music I could no longer hear it at a normal (or any) playback level. BTW, is that AP example at -80 real or simulated? If real, what device did you measure?

    Now let's again look at real music capture using my audio precision:
    What am I looking at?

    Per above, sounds like you want a situation where on purpose, jitter would not be audible.
    I might not have been clear enough. Forget the -60 part unless you can show that jitter is ever that high in functioning gear. All I am asking for is an example where the amount of jitter from a cheap CD player or other consumer digital device is ever audible.

    Show me where high frequency content is at 0db and I buy your arguments.
    Then we're getting closer. Didn't you already acknowledge in your Post #8 that jitter is a fixed level below the signal, rather than steady as is noise?

    --Ethan
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