Topic: Question on jitter graph on page 73 of manual

Hi RME team,

On page 73 in the ADI 2 Pro manual there is the jitter plot of the device.
It can be read very often that the peak at 11.025 kHz should not widen to the bottom, and ideally it should be a single, very narrow peak. I've also seen measurements where the peak is not widening and the reviewer writes that this would be a "great performance".

Now I got curious because the ADI 2 Pro jitter plot seems to widen.

What's the deal with such statements and what's the technical reason for a wide or narrow peak? Moreover is this even important for audio quality / technical performance?

Thanks for a brief explanation.
Andreas

2

Re: Question on jitter graph on page 73 of manual

One can easily get a much narrower skirt at the bottom by doing synchronized measurements, which seem to be the norm. Simply connect input to output of the ADI and you get that. But these measurements are quite misleading (read too good to be true), so I used two units, where one is fed analog into a second unit, unsynchronized, which is a much better real-world setup. By doing so the skirt gets widened, but that doesn't matter at all. What matters is that there are zero (0) sidebands visible. The widening represents lowest frequency jitter at very low levels that stay definitely inaudible.

I have measured many units even with special low phase noise crystals. While most show a bit more narrow skirt, they suffer from lots of sidebands, peaking out of the noise floor up to 30 dB, simply because they have no effective jitter reduction in the audio band.

Finally: if the widening would have any meaning, the ADI-2 Pro would not have the specs that it has - and these have been confirmed by several magazines already.

Regards
Matthias Carstens
RME

3

Re: Question on jitter graph on page 73 of manual

Here are two examples of synced measurements, the standard SR/4 & 192 LSB test signal with 16 and 24 bit. It's always easy to let something look nice wink

http://www.rme-audio.de/img/adi2pro_jitter_16.png

http://www.rme-audio.de/img/adi2pro_jitter_24.png

Regards
Matthias Carstens
RME

Re: Question on jitter graph on page 73 of manual

Hello Matthias,

Many thanks for the explanation which helps a lot.
I've recently bought the ADI 2 Pro for home use and I think it's a phenomenal product.

Just wondering:
The first graph here with signal related sidebands but in the manual no sidebands - both are done with 44.1 kHz?

Greetings
Andreas

5

Re: Question on jitter graph on page 73 of manual

The first graph shows the sidebands caused by the toggling LSB when limited to 16 bit resolution. It must show a slow but continuous decline from left to right (as it does) and no sidebands in-between (as it does). I'm astonished you haven't seen that before, it's the default jitter measurement on many websites and magazines.

Regards
Matthias Carstens
RME

Re: Question on jitter graph on page 73 of manual

Hi Matthias,

of course I've seen such plots.
And I must admit, my "jitter understanding" stops at some point... that's why I'm asking. wink

I misunderstood because I've overlooked that the plot in the manual is 24 bit.

Greetings
Andreas