The Secret Life of HDMI – Part 4
Continuing with our run-down of the different historical versions of HDMI, this week we look at V1.2a then V1.3, arguably the largest revision of HDMI so far.
Compared with many revisions V1.2a was relatively minor and went unnoticed by many. While a number of changes to test procedures were introduced, the change for consumers was the addition of Consumer Electronics Control or CEC.
CEC, where implemented, allows devices to pass control messages from remote inputs to other devices via the HDMI cable. For example, if a TV is in full view of the audience but the AV receiver is hidden in a cupboard, input selection and volume control might be picked up by the TV and then passed to the receiver via HDMI without the need for separate infrared repeater.
While the V1.2 revision of the HDMI standard offered much for computer users the V1.3 revision turned its attention back to potential video performance. A number of advancements where offered to allow the transport of very high quality video and the market responded with quick adoption by manufacturers.
New Features in V1.3
Increased Data Bandwidth
While V1.0 to V1.2 all offered up to 1080p video, it is envisioned by some that the resolution and/or colour gamut of screens will increase further over time. To this end the potential bandwidth of HDMI was increased to a maximum of 10.2 Gb/s to allow for a number of improvements if necessary.
Support for two of these options were formally introduced with V1.3:
The ability to expand the digital resolution of each of the Red, Green and Blue video channels from 8 bits to 12 bits each. In theory this means better colour rendition. This one change requires a 50% increase in data for the video signal!
Broader Colour Space
While HDMI had previously been limited to the HDTV colour gamut, V1.3 extended the possible gamut to cover the entire colour spectrum of the human eye. In consumer terms this is recognized by the term “x.v.Color” and is defined by the IEC 61966-2-4 xvYCC color standard.
While the standard 19 pin HDMI connector was appropriate for fixed equipment the video camera market preferred smaller physical connections. To this end a smaller connector (Type C) was introduced with V1.3 for just this purpose.
Many modern video devices offer some form of video processing. The two most common modes are “Deinterlacing” (the conversion of Interlaced video signals to Progressive Scan) and “Scaling” the adaption of one, usually lesser, picture resolution to a larger one. As an example, any standard definition TV broadcast will require both deinterlacing and scaling to fill the screen of a modern, HD Ready or Full HD flat panel TV.
Both these processes introduce a finite delay in the video picture while it is analyzed, processed and retransmitted. When viewed, any sound will appear before the picture, visually disconnecting the picture and sound. To counter this audio delay is added (normally in the receiver or AV processor) to bring them back in line. This delay is referred to as the “LipSync” setting.
For most of the history of home theatre setting LipSync has been a manual affair but HDMI V1.3 offers the ability for components to talk about the delays the introduce and set an appropriate audio delay automatically.
Next week we’ll take a small diversion to talk about surround sound formats and how they relate to the different versions of the HDMI standard.