Andrew Everard

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May 30, 2007
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OK, here's a brief history lesson:
The original version of HDMI (v1.0) could carry hi-def video, up to 1080P, and PCM, Dolby and DTS digital audio.

  • HDMI v1.1 added support for MLP, which is used for DVD-Audio discs.
  • HDMI v1.2 added support for DSD, which is the SACD audio format.
  • HDMI v1.2a added the capability for the Consumer Electronics Control protocol, which allows you, for example, to press 'play' on the remote control of a suitable DVD player, and have the TV and AV receiver switch to the correct inputs automatically. This of course depends on the equipment being compatible with the system, and is available under various brand names such as Panasonic's Viera Link and Sony's Bravia Theater Sync. In theory, it should be interoperable between brands, but it ain't necessarily so.

HDMI v1.3
has now added the ability to carry the following:

  • HD Audio, including the HD versions of Dolby Digital and DTS
  • Deep colour - the ability to carry up to 48-bit colour information
  • xvYCC colour, for enhanced rendition
  • Higher video resolution, up to 1440p
  • Automatic lip-synch adjustment

All well and good so far, but it's not as clear as it seems. Just because you have an HDMI 1.3 compliant DVD player, for example, doesn't mean you'll get all of the benefits above. You need suitable HDMI 1.3 equipment all the way down the chain - AV receiver and TV. Even then there's no guarantee you'll get all the features if the manufacturer of one part of the chain has decided not to implement them. For example, the only real step forward so far with HDMI 1.3 has been in the audio area, with deep colour, xvYCC and automatic lip-synch yet to be implemented widely.

The CEC remote control system is, as yet, still in its early days, and guaranteed functionality is only possible within one-brand systems. When I visited Onkyo a couple of months back the engineers there were still struggling with this: they said they knew their receivers would give CEC operation with the latest Panasonic Viera TVs, but were still working on checking interoperability with other brands.

Then there's the whole thorny problem of HD Audio itself. Although the hi-def audio datastreams can be carried via the HDMI connection, and receivers are beginning to appear able to decode such information, whether the datastream passes in its native form down the HDMI cable is down to the authoring of the discs.

Almost all HD DVD discs are produced in Advanced Content format, which mandates that their Dolby and DTS HD soundtracks must be decoded in the player, and not let out via the HDMI connection. And as Blu-ray discs move into this format, which will come as more interactivity is introduced, then Blu-ray players will also have to do the decoding.

You can understand why the studios are keen on this - the last thing they want is high-definition video and master-quality audio being allowed out in a form that just could be used for piracy.

Fortunately, the decoded audio is transmitted down the HDMI cable as multiple streams of Linear PCM data to a suitable receiver, so provided the decoding in the player is of a high enough standard, there are no losses in quality when using this way of working.

The alternative, by the way, is to use multiple analogue connections between player and AV amp/receiver: this has the advantage that any older amp or receiver with multichannel analogue inputs can handle the new hi-res audio formats, but does put a lot of pressure on the quality of the analogue output circuitry in the player.

Oh, and the automatic lip-sync thing? It depends on the TV sending a signal back up the cable saying 'I take XX milliseconds to do all the video processing, so slow the audio down by that much please'. But as with all things HDMI, and especially the High-bandwidth Digital Content Protection that can be put on some software, it involves 'handshaking' between all the devices down the chain.

You remember the old noises modems used to make in the dial-up days, when your computer sent out a burst of digital chatter and back came a similar burst? That's handshaking, and unless the devices tell each other their capabilities correctly, some elements of the signal may not be sent or, in a world where everything carries HDCP - no, we're not there yet - the DVD player might simply not connect with the TV.

It's also worth noting that there are some other twists on the whole HDMI thing. HDMI 1.3a essentially suggests very slight modifications to the connector used, making the cable less likely to fall out of the product. That gets a big thumbs up from us, since we're strong believers that the connector should have had thumb-screws like you find on DVI connections to ensure it stayed put: after a bit of the plugging and unplugging we do every day most HDMI connections start to get a bit loose.

HDMI 1.3b is still in the testing stage, and no finished spec is available.

Oh, and there's also an even smaller version of the HDMI connector, known as 'Type A'. This came in with v1.2, and is designed for use on portable devices and the like. You can see it in the picture below - standard HDMI connector on the left, Type A on the right.

A recent trend has been the arrival of HDMI 1.3 cables, which offer the advantage of - nah, don't get me started!

Fact is, over relatively short runs - like a metre or two - any properly designed HDMI cable will deliver all the functions of HDMI 1.3. If, that is, the manufacturers of the equipment all the way down the chain have chosen to implement them.


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