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RME User Forum → ADI-2 & 2/4 Pro series, ADI-2 DAC series → Jitter of a PC-USB interface
With the excellent ADI-2 DAC, you can also make a loop measurement with a jitter signal via USB:
The small differences in the measurement results between different PCs should only be due to the USB interfaces of the PCs, since the jitter of an ADI-2 DAC cannot be measured with this loop measurement (same signal for input/output).
Or have I overlooked something?
ADI-2’s FS clock removes almost the complete jitter - nothing left to measure.
Apart from that there is no USB jitter in an asynchronous design.
Thanks and sorry!
"The small differences in the measurement results between different PCs" were caused by different versions of Multitone. A re-measurement with REW shows: there is no difference!
It is interesting to see what the analogue computer can block out when sensors capture graphics.
PCn[USB]<->ADI-2-DAC-AK4493 (Loopback to USB pre FX)
With the jitter signal from REW (41.1 - 768 kHz, ASIO, dBc, Rectangular) I get a stable value display from the basement in the RTA window. With Multitone (..., dBr, Blackman-Harris 7) it goes down a few more floors.
For SR 48 kHz:
-140.8 dB @250 Hz (-145.6 dB with Multitone v1.0.97).
Symmetrical to 12 kHz:
-143.9 dB @11.750 kHz (-148.5 dB with Multitone)
-144.2 dB @12.250 kHz (-148.8 dB with Multitone)
All other values are lower.
Same values for other SR related to lowest frequency and the two symmetrical frequencies to the carrier.
Multitone isn‘t well suited for jitter measurements.
Non-linear distortions could easily be confused with jitter, specially IMDs.
Not easy to find a configuration that works with such low values to be expected.
You need a reference clock that’s better than ADI-2’s 
Maybe this one can help, it’s distortion figures are, according to my measurements, better than -155 dB, this is 30 dB better than ADI-2’s resolution:
Victor Mickevics Ultra Low Distortion Sine Wave Generator.
https://viccc42.wixsite.com/uld-audio
http://archimago.blogspot.com/2022/01/u … rence.html
Never used it for jitter, built a jig to measure capacitor distortions.
For very low value measurements you need time (larger FFT, more data points etc). The Victor oscillator is not perfectly suited for that as it's base frequency is unstable and wanders, mostly temperature caused. Otherwise it is very nice (got these myself).
For very low value measurements you need time (larger FFT, more data points etc). The Victor oscillator is not perfectly suited for that as it's base frequency is unstable and wanders, mostly temperature caused. Otherwise it is very nice (got these myself).
The exact reason I gave up on the project after getting very promising results.
The generator has a very low noise floor too, BTW.
At that time I used an AD with ca. -110 dB distortions and noise.
So the notch filter for the fundamental needed to be quite steep and therefore very frequency dependent.
The oscillator’s frequency drift even after long warmup made the measurements too complicated.
Now, with ADI-2/4 Pro SE at hand I‘m tempted to give it another try.
Back to topic, @MC:
Jitter measurements based on a single 1 kHz analog sine wave - worth considering?
You wouldn‘t need an extremely long term stable frequency, I think.
Or will this just confirm there‘s no measurable jitter on ADI-2?
> Jitter measurements based on a single 1 kHz analog sine wave - worth considering?
You need to give some more details...
> Jitter measurements based on a single 1 kHz analog sine wave - worth considering?
You need to give some more details...
Low distortion (and noise) analog sine wave generator
-> ADI-2 Pro or 2/4 Pro SE analog in
-> USB
-> FFT analysis with suiting resolution to show possible sidebands that indicate jitter.
Makes sense / worth to try?
ADI-2 Pro manual page 88 shows such a measurement, but DA - AD from the same device, so jitter, if exists, might not show up due to common clock.
With my old setup (Orion 32) I got this, no jitter visible:
Victor Mickevics Ultra Low Distortion Sine Wave Generator.
https://viccc42.wixsite.com/uld-audio
http://archimago.blogspot.com/2022/01/u … rence.html
Thanks, but I had already followed the development from 2019.
If anyone would like to read the development of Victor's (vicnic) very interesting LOW-THD Oscillators:
https://www.diyaudio.com/community/thre … 4/page-365
REW 2023-10-14 - Behaviour of coherent averaging for tones that are not FFT-locked
https://www.avnirvana.com/threads/%E2%8 … ing.12631/
My measurement described above was saved under ADI-2-DAC-AK4493 Diagnostic Test-1. If there were problems with the interface, it could be compared with the saved REW measurement.
RME User Forum → ADI-2 & 2/4 Pro series, ADI-2 DAC series → Jitter of a PC-USB interface
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