Jitter, What does it measure

[blackmagic]

Already put this post in another forum but didn't get any answers so i'll try here. I was wondering if anyone could answer these few questions about jitter.

1. What is it and what does it actually measure?

2. What numbers should your jitter be between, is lower better and what's too high?

3. Does the shape of the jitter graph mean anything or are the numbers all that matter. Eg. does the average jitter level make the biggest difference or is it best to have a flat jitter graph with a higher average level.

4. I've occasionaly jot jitter graphs that will have a thin downward spike on them. do these downward spikes have the same effect as an upward spike or are they good.

Thank you

[edDV]

Are you taling about DVD jitter or video jitter? You are looking at something you call a "jitter graph". It could be NASA reentry telemetry for all we know. Provide info about what you are talking about.

Video jitter is phase distortion or instantaneous speed changes. It can affect horizontal pixel position and color phase decoding. More is bad.

It is especially bad for broadcast TV since subcarrier is locked to h phase. H-phase precision needs to be in the nanoseconds. That is why direct recording of NTSC or PAL is more difficult than component recording.

VHS VCRs break this relationship to H with the color under recording process.

Capture cards decode the NTSC/PAL to YUV components so jitter only affects pixel H-position stability.

[lordsmurf]

Jitter measures in software like kprobe, as I gather.

[pompoi]

The jitter shown on nero cd dvd speed extra`s disc quality is as far as I have been able to find out a measure of audio jitter.
The max level for measuring quality seems to be 11% above this is concidered poor.

[blackmagic]

Yes i was refering to jitter measured in programs like kprobe.