[sonance]

So now that there are standards for non-proprietary uncompressed multi-channel audio over a single cable, and more HDMI capable receivers and pre-processors being released and announced, I wonder how long it will be before we see DACs with HDMI input?

I'm quite curious to learn if HDMI DACs will be jitter free in some situations - when using lossless DTS / Dolby encoding, since the bistream is variable bit rate packed (unpacked by the receiver / DAC), and not slaved to the transmission clock?

The PS3 can output CD and SACD over HDMI, there are DVD-Audio solutions as well, and BD and HD-DVD support lossless audio over HDMI as well.

On the PC front we've seen ATI release mass market motherboards with integrated HDMI output (including audio) and the rumor is ATI's next batch of cards will support protected path audio over HDMI as well, so we should have options for all the common sources of audio.

Of course since HDMI also includes video (potentially), the DACs would need to pass-through the HDMI so that the video portion can be passed forward.

It would be great to exclude jitter as a consideration and just focus on the actual analog conversion part of it, but it would also be nice to have music be part of this brave new world of high definition video and audio over a single cable.

 

[Garbz]

Hate to say it but jitter via HDMI could probably be worse. Look at the connector pinout. Only one dataclock

I'm pretty sure the clock would run at a frequency related to video not audio. The end result would probably be the same **** jitter characteristics as every other player that has a 27Mhz clock and then needs to approximate the audio frequency clock from it.

 

[sonance]

While PCM data over an HDMI connector would be prone to jitter, a lossless compressed or packed data stream would be unpacked in the DACs buffer, and the resulting data has nothing to do with the transmission clock. The DAC could have it's own independent clock for the DAC stage feeding off the buffer, which is not connected to clock of the received data. And I'm talking about a separate, audio only DAC for HDMI.

Wouldn't that eliminate jitter, depending on the HDMI DAC's design?

 

[hciman77]

Quote:

Originally Posted by sonance /img/forum/go_quote.gif While PCM data over an HDMI connector would be prone to jitter, a lossless compressed or packed data stream would be unpacked in the DACs buffer, and the resulting data has nothing to do with the transmission clock. The DAC could have it's own independent clock for the DAC stage feeding off the buffer, which is not connected to clock of the received data. And I'm talking about a separate, audio only DAC for HDMI. Wouldn't that eliminate jitter, depending on the HDMI DAC's design?

Any DAC that buffers words of data and then clocks them out independently would negate the effect of any timing variations in the delivery of data to the DAC. The fact that so few DACS incorporate such mechanisms makes me think that most DAC manufacturers dont consider jitter to be a big issue.

 

[thomaspf]

Buffering alone does not help. Most surround sound receiver do buffer and decompress the signal into discrete 5.1 analog channel but they still directly derive the conversion clock from the incoming signal. In that case the input jitter directly affects the conversion independent of buffering in between.

That's one of the reasons surround sound units often do not compare well to dedicated DACs.

Cheers

Thomas

 

[Garbz]

You can buffer all you want, but in order to prevent buffer overruns or underruns you still need to derrive the new clock form the incoming clock, or get creative. The former is the reason that a buffer does not solve the problem, the latter is the reason so few DACs incorporate "proper" jitter reduction. (Larvy is one that does, Benchmark is another, both are considered up with the best).

 

[prone2phone]

it was year 2007 and now?

 

[josep]

AFAIK, only recently Sony come up with 'something': it HATS system (only available on SCD-5400ES player and matching receiver) uses buffering and clocking control from receiver to player and has been measured under 200ps jitter via HDMI (vs over 8,000 with the system disabled). I tried it, and liked (it works great).
But right now this is a propietary system, invented by Sony, a maker know for other nice inventions that finished on the bin... (Betamax? MiniDisc?)
So who knows.