Sound options ATV-TV-AMP Surround to Stereo speakers

Hi, first of all I’ve read https://support.firecore.com/hc/en-us/articles/217735707-Audio-Options-tvOS- and many other forum topics regarding this and I’m just wondering. I have Infuse PRO (not much to change reg. audio) on ATV4k connected to Sony XE9005 (X900E) (selected PCM output from optical out) via HDMI cable, optical cable from the TV to high end amplifier and to a set of stereo speakers.

My questions:

  1. What happens with sound from the start (ATV) to the end (amp/speakers) if selecting e.g. DTS-HD MA or TrueHD? What will do infuse/atv/TV/amp with audio track - converting/downmixing/compressing etc.?
  2. Is there any difference if I choose AUTO or STEREO audio output setting on ATV?
  3. Is surround audio properly downmixed to 2.0? - Are all channels compressed to create a stereo sound or are surround channels removed completely, what about SUB channel?
  4. When there are multiple audio tracks, is it better to choose STEREO track or the high quality lossless SURROUND?

Thank you.

Welcome to the forum!

  1. When playing these audio tracks, Infuse will send the full uncompressed audio to the Apple TV for it to pass along to your receiver. Depending on your settings, this audio may be reformatted. See below.
  2. The settings probably won’t matter, as the optical cable is going to be a bottleneck. Toslink supports a maximum of 2ch of uncompressed (LPCM) audio (or 5.1 compressed) so the Apple TV is likely going to choose the Stereo option for you. In this case, Infuse will send the Apple TV 7.1 audio, and the Apple TV will downmix it to 2.0 audio. If you were to eliminate this optical cable, you would be able to get 7.1 LPCM to your receiver, which could then handle the change to 2.0. It’s also possible the Apple TV sends 7.1 to your TV, and the TV then does the downmix to 2.0. It just depends on what the Apple TV senses is on the other end of the HDMI cable.
  3. Apple’s downmixing process is a bit of a back box, but it likely uses the 3 front channels only.
  4. This will likely be a personal preference, as there could be some minor differences between a dedicated stereo track and Apple downmixing a 7.1 track to 2.0.

Hope this helps!

1 Like

HI James,

Thank you, your answer is more than I hoped for.

One more question, will the downmixed audio from lossless TrueHD/DTS-HD MA to PCM 2.0 be lossless too if downmixed on ATV or TV?

Have a nice day!

I believe the answer is yes to both, but can’t say for sure since Apple and TV manufacturers don’t disclose the exact processes they use.

If you set the Apple TV audio output to ‘Dolby Digital’ the Apple TV will definitely convert it from lossless to lossy.