Coaxial SPDIF experiment

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onlyoneme

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to get an eye-pattern. An ordinary RCA analog cable used, terminated with 50 ohm and a PicoScope 4444 oscilloscope working with 20 MHz BW.

48 kHz:
48.png


96 kHz:
96.png

192 kHz:
192.png

Any thoughts? :)
 
Spdif coax spec is 75 ohm if I remember it right. 1.2 m minumum length. Not sure how that might affect your results..
 
OldNick said:
Spdif coax spec is 75 ohm if I remember it right. 1.2 m minumum length. Not sure how that might affect your results..
Click to expand...
I know, but I was getting much worse visualization when terminating with 75 ohm. Maybe the cable I've used is closer to 50 ohm. No idea what's the impedance usually for analog RCA cables.
 
A short explanation - I'm trying to figure out how a cable can influence the carrier jitter and noise for different sample rates.
 
If only it was as simple as that! it would put reviewers out of business overnight.

look at audio science review website for ways of using scopes to see Jitter (and basically how insignificant jitter is in the world of modern Dacs)
 
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a 20mhz is not enough for this kind of observations
;-)
(
the rise times of the scope are too long for a relevant observation...
;-)..
but an example of a really clean 44/16 signal at the output of a drive..
but again on a too limited scope like 50mhz .. the rise time marred by 7ns plus a little the probe ...to do well, you need 350-400mhz mini and adapted probe..i have but..not wiim pro i cant help...
 

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If I'm reading it right, you're showing that the digital signal degradation increases with the increase in frequency?
Isn't that to be expected?
 
canard said:
a 20mhz is not enough for this kind of observations
;-)
(
the rise times of the scope are too long for a relevant observation...
;-)..
but an example of a really clean 44/16 signal at the output of a drive..
but again on a too limited scope like 50mhz .. the rise time marred by 7ns plus a little the probe ...to do well, you need 350-400mhz mini and adapted probe..i have but..not wiim pro i cant help...
Click to expand...
Why? SPDIF frequency for 192 kHz is less than 13 MHz.
Different cable, still 50 ohm, different triggering.

48 kHz:
48.png

96 kHz:
96.png

192 kHz:
192.png
 
it's just that you don't have enough margin..
the rising edges are tainted by the slow rise times of the 20mhz
(350/20...17.5ns...350/50..7ns etc)
It makes reading a bit clumsy...
etc
;-)
 
no, I have nothing on hand.(but these are square signals..explain the difficulty for a scope without a large margin in bw...)
automatic edge calculations give how many ns?...(x-17.5ns?)
(from memory the example I show was a + 3.5 4ns+7 type of flipflop output...)
but it's not a standard 0.5v spdif output?
 
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ps
I would like to know if wiim has put a transformer in spdif output
but we still don't have a photo.
but if there is one side external dac .. not a problem
 
Last edited:
canard said:
no, I have nothing on hand.(but these are square signals..explain the difficulty for a scope without a large margin in bw...)
automatic edge calculations give how many ns?...(x-17.5ns?)
(from memory the example I show was a + 3.5 4ns+7 type of flipflop output...)
but it's not a standard 0.5v spdif output?
Click to expand...
It's a standard spdif output but impedance mismatch - 50 ohm termination plus a cable - probably affects a voltage.
I know I won't get a square wave representation, I don't expect this. But I think the noise and jitter can be still observed on the pattern.
 
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