I have a DAC that I can run the outputs of into my PC soundcard. I am wondering what software could be used (preferably free) that could measure the jitter of this signal.
If it makes a difference I could also run the SPDIF signal into the PC soundcard. Thinking about it that may be a better choice if it doesn't clip.
Thanks,
vladimirb0b
If it makes a difference I could also run the SPDIF signal into the PC soundcard. Thinking about it that may be a better choice if it doesn't clip.
Thanks,
vladimirb0b
There is no jitter on the analog output, it is a phenomenon in the digital domain. Measuring jitter would need a precision instrument, a soundcard will not do, IMHO.
This isn't true, the jitter present within the digital signal causes artifacts to appear on the analogue output. Some DAC architectures are better at suppressing this than others.
I would be measuring jitter on the S/PDIF connection, and possibly analog output too.
This thread: http://www.diyaudio.com/forums/digital-source/183110-jitter-test-signal-j-test-signal-matlab-2.html has some wav generating programs to test for jitter. I'm just not sure how to play them back and analyze/record the jitter.
Some might say that the soundcard audio input and output jitter will dominate. Well, that is just fine, and it would still be useful to measure. If that jitter is, for instance, less than 10 ps I would know that no further jitter reduction is needed.
The first is irrelevant- the ONLY jitter that matters is at the DAC clock. And that measurement is extremely difficult and expensive. You CAN see the effects of jitter in the analog output (the J-test is one method), but you can't translate it to time specs.
Just to put it in perspective, testing has shown that the audible threshold is in the nanosecond range. It takes a pathological DAC to get anywhere near that- there may be some high end unit designed by a former salesman that is that bad, but any DAC put together by competent engineers won't have that issue. Jitter is the Emmanuel Goldstein of fashion audio- several of us posted J-test results from fairly cheap DACs a few days ago, and nearly all looked fine.
There's no such thing as "jitter" in an analog signal by definition. If there's jitter at the DAC clock, then the analog signal will show noise and/or distortion, but that's not jitter, that's... noise and distortion.
BTW, you can get a much better understanding of the issue by reading Bob Adams's superbly clear article explaining how jitter affects DACs and why jitter measurement is a red herring. starts on page 11.
http://www.biline.ca/audio_critic/mags/The_Audio_Critic_21_r.pdf
http://www.biline.ca/audio_critic/mags/The_Audio_Critic_21_r.pdf
Thanks... However I am still curious to measure my DAC with a J-test. I imagine others are too. Could you post any links you have with instructions/parameters and software info? Will arta do the job or is other software needed?
For those out there: ARTA has a Jitter Test function under the Spectrum analyzer. Still trying to get a strong signal to show up but that's, I believe, what people have been using.
That's what I've used. Some DACs have a noise floor too high to see the jitter signal. It's only on the LSB on the ARTA test.
I am getting a noise floor at around -125dB with a signal of about -85 dB at around 11KHz. Anyone know if it is possible to raise that signal?
May look at my site on HpW Tech 6: Jitter Fs/4 signal & LSB Toggle at Fs/192
Also, look at the front page slideshow about some measurements I did.
Hp
You have a bad hum loop somewhere in your setup. With a bit of care, you can get the hum components below -100dB. Also, try setting the display to linear frequency- it gives a more sensible display.
edit: try copying the settings I used in this spectrum.
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