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In Reply to: Is HDMI interface better than the old S/PDIF for digital audio ? posted by beppe61 on April 8, 2007 at 05:01:26:
HDMI can offer multi-channels and high sample rates that are simply not possible from S/PDIF. Performance-wise, it is a mixed bag.HDMI does have a separate clock signal, unlike S/PDIF where the clock and data are embedded together. However the clock signal is the 27 MHz *video* clock, and the audio clock needs to be recreated (presumably via PLL's) from the video clock. So it's not clear that there is much to be gained there.
Finally, HDMI comes along with a video signal, which means that in general there is a also a video display now hooked up to your audio system. Hooking up a video display is the single quickest way to degrade the sound of your audio system.
Better than HDMI is I2S, where the clock and data are separate. However, this was only ever implemented by a couple of small companies (eg, Camelot). Better still are the systems where the clock is sent "upstream" from the DAC box to the transport box. This was only ever done on a proprietary basis by a few people like Linn and Wadia.
I tried to organize a standard for doing this so that all high-end digital audio components could be compatible, but there was too much political infighting to ever achieve success. This eventually became the "SyncroLink" system that is on the Ayre DX-7e DVD transport. We will implement the other half in a DAC box, maybe later this year.
Follow Ups:
s
Thank you very much indeed Sir for the kind and thorough explanation.
Kind regards,
bg
HowdyOne other problem I've noticed with HDMI, since it by spec provided power and ground there is no possibility of having a ground loop isolating device (hum buster, etc.) in a true HDMI connection. I had just got the last bit of hum out of my system with S-Video isolation transformers between the Tivos and the TV when I got a HD Tivo with HDMI... I'm going to use a gas discharge ground isolator at the dish to fix things right, but HDMI definitely can cause problems...
The problem as I see it is there is nothing technically preventing the powers that be within the standards forming groups for HDMI from developing some breakout interface for audio which can be electrically isolated. For example ecrypted data can be passed over ethernet and that can be electrically isolated. I'm not trying to say ethernet is the best choice just using an example of an industry standard data transfer method that already exists that could handle the job just fine.I predict the HDMI idiots can try making all the weekly standards updates they want but until they come up with some assurance that equipment based on these standards won't be immediately obsolete, good luck selling these "visions" they are having.
I think I am starting to come around to Charles' way of thinking. It is ridiculous to pass the video information to the reciever. Companies that invite the marketters to design meetings should not exist. What a mess.
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