PCM, HDMI and jitter

[Brandon B]

It occurred to me I don't know, and am curious. Is PCM over HDMI (i.e. for lossless codecs on HD disks) packetized and reclocked like DD and DTS such that is immune to jitter? Or is the clock derived from the bitstream as it is on S/PDIF?

I would assume the former as 8 streams can be going all at once and cable length seems to be less of an issue, but was not sure.

BB

[Brandon B]

Nevermind, found my answer.

http://www.interfacebus.com/HDMI_Pinout_Bus.html

HDMI has clock signals sent separately, so it should not really be an issue.

So a new question then. Would normal redbook PCM perform better over HDMI assuming your system performance was being degraded by jitter in your SPDIF link, or would the clock be ignored/not used for the older data format?

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[ToddAnisman]

Nevermind, found my answer.

http://www.interfacebus.com/HDMI_Pinout_Bus.html

HDMI has clock signals sent separately, so it should not really be an issue.

So a new question then. Would normal redbook PCM perform better over HDMI assuming your system performance was being degraded by jitter in your SPDIF link, or would the clock be ignored/not used for the older data format?

BB

Brandon-

Most receivers will auto sync to the incoming word clock from the Digital signal coming into it that has been selected to listen to. I am not aware of a processor that can take an external Word Clock signal and clock to it.

Now to the question of jitter- There's no way you can know that you're having a jitter issue unless you have a serious O-Scope that you can put across your outputs in order to measure the Jitter. Also, Jitter rarely occurs in a single connected environment like a Home Theater system, where it' sonly one line at a time thatis being clocked and output. usually it occurs in larger systems where hundreds of discrete signals are being worked with, and the disparate clocks cause that distortion or jitter in the clock.

So that being said, i wouldn't go so far to say that Jitter is a complete non-issue, but I don't think it's going to affect you in the kind of way that will cause you issues or sonic degredation. The guys at Euphonix (serious high end Pro Audio Console designer) basically have told me repeatedly that the input will either lock or it won't... take that for what it's worth...

-Todd A.