The latest version of HDMI — 1.4 — provides for, amongst other things the Audio Return Channel. You have a HDMI cable from your home theatre receiver to feed video to the TV. ARC allows this very same cable to carry sound from the TV back to the home theatre receiver.
To make use of this you need a TV and a home theatre receiver which both support the feature, and then to switch on all the HDMI control stuff. In general, if you have the home theatre receiver on, then when you select the built in tuner on your TV to watch TV, the receiver will automatically switch to the ‘TV’ input and receive the audio signal. No sound will come out of the TV’s speakers. When you use the TV’s volume control, it remains silent but the command is sent through to the home theatre receiver, and its volume changes.
Sounds good, eh?
Except for the side effects. Generally, switching off the TV also switches off the receiver — even if it isn’t switched to the TV input. If you were listing to a CD and decided that you didn’t want the TV on, then off goes the receiver as well and your music stops. With some equipment, when you switch the receiver on it is always set to the TV input.
And right now, I’ve just switched on the system and here’s the situation: the TV is showing the picture from a PVR plugged directly into it on HDMI 3. The TV is also connected to the receiver on HDMI 2, which supports ARC. The receiver is switched to the DVD input, into which a Blu-ray player is plugged. The sound coming out of the main speakers is that from a movie playing in the Blu-ray player.
I pointed the TV’s own remote control at the TV to turn it up so I could hear what was on playing on the PVR. The TV took that volume command and sent it down the other HDMI cable to the receiver, turning up its volume so that the Blu-ray was playing louder.
Switching off all these control features may be the only way to make the system work at all predictably.