Since a also have the Theta Casablanc, with HMDI, I could add the AppleTV, but generally speaking HMDI is bad for audio.
Uhm, not much wrong with HDMI if the processor is doing appropriate clocking. And encoded streams, such as TrueHD or Dolby MAT, are re-clocked during decode to LPCM by the processor and therefore not subject to HDMI jitter.
The ATV is an amazing piece of kit, I have both the older and the 2021 variants of it. 80% of my media consumption is done using it either in the media room or the HT (HT is more weighted towards BluRay these days).
As a massive multichannel and immersive audio fan (4 Atmos-capable reproduction chains here), I'm super excited about Apple Music supporting Atmos now.
As part of explorations about details of how all this functions, I wrote up the following to explain to others how Atmos streams are propagated from an ATV4K to one's processor.
First, the current status for the source sent from Apple Music is that the incoming stream is a DD+ at the max rate of 768Kbps.
My understanding of what the ATV4K does is the following:
- De-muxes the audio and video streams
- Routes the video stream to the HDMI, with any necessary conversions, or none, based on settings and EDID info from the target device
- Decodes the audio stream elemental parts, in the case of DD+ into the (up-to) 7.1 LPCM bed channels and the encoded Atmos objects data stream.
- It then encodes (see below) all that into a Dolby MAT 2.0 stream and transfers that over HDMI to the processor
Thus, in the case of Atmos, HDMI jitter is not an issue, as it is an encoded, containerized datastream that the processor will decode and re-clock the LPCM internally.
Note: MAT 2.0 is a codec where the source (ATV) encodes a mix of signals, in this case, the (up-to) 7.1 LPCM bed and the Atmos objects streams into an 8 channel 16/192 'carrier' LPCM stream whose headers tell the receiver that this is a MAT 2.0 encoded stream.
So with 3MBs per 'channel' * 8 = 24MBs (and that's bytes, not bits) we have very high-capacity data transport over the HDMI link.
MAT can be used to send lossless content if the source has it, it can even propagate TrueHD compressed lossless IIRC.
So at some future date, Apple Music *could* stream TrueHD Atmos, and the ATV4 will re-package it into MAT 2.0 (or 2.1), as there is plenty of bandwidth over HDMI.
So technically, the ATV is sending a MAT 2.0 stream at all times if the processor supports MAT. Because the ATV is encoding the MAT stream, it can overlay UI feedback into the audio stream before encoding.
I have yet to validate that 'lossless' 2-ch music is sent over MAT or plain LPCM. Either will handle the required bit-depth and sample rates, but they might downsample plain LPCM to 24/48 for purposes of adding UI feedback. But hopefully not if one picks the 'no audio feedback' option in the settings. Off to play with all this.
