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Old 9th March 2004, 02:45 AM   #1
pop11 is offline pop11  Canada
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Default Jitter measurement

What's the best and cheapest way to measure the jitter of a CD player?

Thanks.
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Old 9th March 2004, 07:00 AM   #2
EDUM is offline EDUM  Netherlands
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Very good question pop11!

In the past (yes, already some time ago) I did for Philips a comparisson of all available commercial jittermeasurement equipment. That plus the available inhouse references made a "complete" picture. The result was that none of the tested commercial equipment gave results that would qualify them as measurement equipment. Yes, it was that bad.

As it was in the interest of Philips to have reliable external measurement equipment available I expect they trained some companies to be able to do correct measurements.

So I hope any available equipment nowadays is able to do correct measurements. If so I am afraid it will not come cheap.

But if you are a handy DIY-er I sugest you look at the CD standard and give it a try to design something for yourself. It least it gives you a deeper insight in this jitter matter.

Success!

Ward
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Old 9th March 2004, 07:04 AM   #3
hifi is offline hifi  Sweden
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New DAC with measurements!

http://www.mindspring.com/~ojg/DAC1704/DAC1704.html

http://www.nanophon.com/audio/diagnose.pdf
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Old 20th January 2009, 08:55 AM   #4
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Rather than starting a new thread, maybe revive this one?

I have had the opportunity to play with an Audio precision System 2722 a few days. One measurement I did was on a sample rate converter, to see what the jitter performance was.

The attached shows one particular measurement I did. What I didn't realize first was that if your input signal has jitter, but you use the clock extracted from that input (which of course also has jitter) than your output from the SRC has no jitter at all (BLUE curve).
OTOH, if the SRC uses a very stable external clock that has no jitter, the output of the SRC does have all the jitter present in the input.

Am I the only one that didn't realise this?

Jan Didden
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File Type: pdf fig 1.pdf (10.6 KB, 173 views)
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Old 22nd January 2009, 10:03 AM   #5
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"Am I the only one that didn't realise this?"

I guess you are the first to realize that. Very interesting.
You use jittery input clock also as your output clock to DAC? An you get no jitter sidebands measuring analog output?
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Old 22nd January 2009, 10:18 AM   #6
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Quote:
Originally posted by borisov57
"Am I the only one that didn't realise this?"

I guess you are the first to realize that. Very interesting.
You use jittery input clock also as your output clock to DAC? An you get no jitter sidebands measuring analog output?
No, the analyzer was looking at the AES output of the SRC. I didn't check after the DAC, I should have...

Jan Didden
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Old 22nd January 2009, 12:08 PM   #7
Gopher is offline Gopher  United Kingdom
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Jan

I'm confused. I thought the whole point of using a SRC as a jitter eliminator was that it is clocked asynchronously using a jitter free external clock not related to the input data clock. Is that not the case?

Perhaps a diagram would help illustrate exactly what you're talking about here?

What SRC was it you investigated?

Gopher
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Old 22nd January 2009, 01:11 PM   #8
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Quote:
Originally posted by janneman


I didn't check after the DAC, I should have...

But System 2722 is gone?
Measuring sabre DAC, better clock translates to lower sidebands on analog output. I have never measured TI or AD ASRC, but maybe I should.
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Old 26th January 2009, 04:54 PM   #9
alvaius is offline alvaius  Canada
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Jan,

If I am not mistaken, the test you are doing is only looking at the audio embedded in the data, hence it is not at all looking at the jitter in the timing, but only any artifacts in the data stream?

If this is the case, I "could" see if the input and output clocks are the same and without too much jitter, the output data would look exactly the same as the input data. As soon as you have a new output clock, the output data will not be exactly the same as the input and there will be artifacts. The ones you show in your graph though look quite severe.... I wonder if something else was not going on.

Alvaius
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