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Join Date: Mar 2007
Location: Long Beach, California
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Pardon me if I seem to get into too much detail.
HDMI, as a medium, has no jitter. If there is jitter from an HDMI source, it is completely the fault of the receiver. That is because the audio over HDMI is completely devoid of timing - the audio is sent over HDMI as data during the video retrace intervals, and it is up to the receiver to reconstruct the timing. So if you could hear any jitter, it is caused by poor timing in the receiver.
On the other hand, an S/PDIF optical connection does have bit-timing over the connection, and this timing, if passed all the way through to the DAC chip and is used by the DAC to reconstruct the audio, can have some jitter. However, few receivers use the optical connection's timing directly (those days are over). Rather, they resample the audio data with their own internal clock to drive the DAC.
Not surprisingly, the clock that the receiver uses to render the audio over HDMI would be the same clock it uses to render the audio over S/PDIF. So most receivers will have identical jitter, no matter which source you use.