Control4 / Apple TV Audio dropping

Where this came from: this question was asked on c4forums/Question & Answer — not here. We answered it there, in public, and this is that answer.

Nothing in this is Control4's fault, and there's nothing here to open Composer for. The C4 Apple TV driver drives navigation and transport over IP; it has no hand in what audio format the Apple TV negotiates. So don't let anyone bill you for a service call on it. This is an HDMI handshake problem between the Apple TV and the Yamaha, and it is a common one.

The tell is the fix. Toggling Auto to Dolby 5.1 and back makes the Apple TV tear down and rebuild its audio output, and that's what brings the sound back, not the format itself. That points at the link losing the audio stream and nothing on either end renegotiating. Atmos off an Apple TV is a much fatter, more fragile bitstream than plain 5.1, which is exactly why 5.1 rides through and Atmos doesn't.

So my first move would be the cable, not the settings. If the Apple TV is in the rack, that run is probably bundled with a dozen other things, possibly coiled, possibly bent hard at the back of the Yamaha. Swap in a short, known-good high bandwidth cable straight from the Apple TV to the Yamaha and run it for a week. Cheap test, and in my experience audio is the first thing that goes on a marginal HDMI run while the picture still looks fine.

Second thing I'd try, and try it separately so you know which one fixed it: turn off Match Content, both Match Frame Rate and Match Dynamic Range, under Video and Audio. Every time those kick in the Apple TV changes its output timing mid-stream, and I've seen that leave receivers with picture and no sound. If your dropouts happen at the start of a title or at a scene change rather than at random, that's your culprit.

Also worth telling me what sits between the Yamaha's HDMI output and the theater display. If there's an extender, a matrix or a balun in there, the EDID the Yamaha sees can get rewritten and the Atmos capability can come and go with it. Same question for how the Episode is being fed off the Yamaha, because if that's on a second HDMI output it's part of the same negotiation.

One consolation while you're testing: on most Atmos receivers, running the Apple TV at Dolby 5.1 does not mute your height speakers, the surround decoder upmixes into them. Worth confirming on your Yamaha's setup menu that the surround decoder is set to the Dolby upmixer rather than straight, because if it is, staying at 5.1 costs you object placement, not the top layer entirely. Tell me the Yamaha model and firmware and which Apple TV generation it is and I'll tell you whether I've seen that pair misbehave.

For disclosure, I'm a Control4 and Lutron dealer and have been since 1999. This one isn't dealer work.