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Jitter measurements with the Audio Precision APx555

Hanzu

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Feb 15, 2023
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Hello all,
at the moment, I want to realize a measurement for the university, where I want to test ADCs and DACs for their jitter robustness with the APx555. I am in contact with Audio Precision support, however I thought I might ask you guys as well since I am sure someone here has already done the measurement I am looking for.
I've already had done a couple of experiments where I run the jitter measurements in bench mode with the jitter generator. Now I would like to alternatively perform the "Jitter Frequency Sweep" measurement in "Sequence Mode". To be exact, the "Average Jitter Measurement" of it. Now it is so that one can unlock this measurement only if one sets in the Signal Path -> Input ->Measurement: Jitter(sec)/(UI). So it is assumed that the input must be digital. Therefore I thought that I have to take the output analog. Jitter is only perceptible when a conversion is made. However, I only get noise out of an analog output signal. But if I also take a digital output signal, I get values which I expected with an analog output signal:

Versuch3.jpg

I measured with 40ns Jitter.

Now is the big question:
What do I measure at all when I measure digital to digital jitter.
First, I thought that on the digital level it doesn't matter how much jitter is present, as long as the signal is still decodable, you can remove the jitter.
Second, if the digital signal is simply passed through, then yes exactly the same jitter values from the input should arrive at the output. So what is the point of this measurement then? Or where is my mistake? Maybe someone of you knows.
I hope I found the right forum section for this question, it's my first post and I'm open to suggestions for optimizing my question.
 
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