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Old 11th October 2013, 05:24 AM   #1
xymox1 is offline xymox1  United States
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Default HDMI video jitter questions

Ive been playing with mods to a Oppo. im finding really visually obvious, and measurable, changes when I place caps in places like supply rails to HDMI drive chip.

Ive seen fairly dramatic performance increases in pic quality. However I have also seen degradations too.

I cant measure the eye pattern of HDMI, its just to high a freq for my test gear. Also measuring HDMI jitter is WAY beyond my price grade for test gear.

The changes in picture seriously puzzle me. Digital it appears in this case is not working perfectly. I should not be able to effect picture by changing power supply caps. It was kinda my assumption that HDMI *picture* was perfect right up till you lost picture. Clearly this is not the case.

How is this possible ? I can measure off my Panasonic ST60 plasma differences in luminance of dark areas of the picture with changes in power supply caps. This has me vexed. How is this possible ?

Lets say HDMI has jitter, which we know it does pretty much at all times. If I increase jitter what will this look like ? Can it change the actual digital values without producing obvious errors ? Is there some form of error correction that can alter the values of the digital signal ?

I simply dont understand this. Its almost like the HDMI signal is actually analog. Sure on some level it is a analog signal with digital levels.

Also does anyone know of any white papers or studies on how HDMI jitter effects perception ?
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Old 11th October 2013, 05:34 AM   #2
xymox1 is offline xymox1  United States
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Wow there appears to be ALOT going on.


( s i g h )

And without $250,000 in test equipment its really hard to know whats really going on..

I will try and look with a good scope... But I think I really need a 1Ghz scope with digital phospher to see these eye patterns..

I sure would like to see the state of all the "error correction" on the sink.. Do rcvr chips on sinks have any form of output to show all the parameters of a link and its quality ?
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Old 11th October 2013, 05:39 AM   #3
xymox1 is offline xymox1  United States
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Right from the HDMI spec.. "Sample
repetition and interpolation are well known concealment techniques and are recommended."

So well before you loose pictiure, all sorts of quality changes occur. Well I suppose this explains what im seeing. Im making my link better and it shows, or i add a cap in the wrong place and it creates more errors by degrading the eye pattern and the error concealment gets worse and the picture degrades..
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Old 14th October 2013, 12:03 PM   #4
marce is offline marce  United Kingdom
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Why are you messing about with de-coupling for the HDMI chip, without the correct equipment and much clue at what you are doing or playing with!
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Old 14th October 2013, 01:29 PM   #5
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Agree with Marce. I have listened/watched the Oppo and read reviews of it, and I think it is very good as is. Only with extensive knowledge of this piece of kit and the appropriate measuring equipment can improvements, if any, be expected to be made.

Do you experience problems with sound or video at the moment?
An FFT of my life would show a couple of peaks and some low level harmonics, but mainly random noise.
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