Audio question and how ATV4k works

Hi everyone

I am a little confused.

I guess my question is, if the Apple TV can decode DTS HD and Dolby Digital True HD 7.1 and send the audio as 7.1 LPCM to your receiver / sound system, does your receiver or sound system truly need to know how to decode DTS or Dolby Digital, and that the only requirement is that it can play LPCM 7.1?

My question is if my soundbar doesn’t support DTS HD, does that mean when Apple TV decodes the audio, sends it out at 7.1 LPCM, my sound system would be able to output the DTS HD track?

Or does the DTS / Dolby Digital magic get also sent with the 7.1 LPCM data so that the receiver still needs to know how to handle the DTS or Dolby Digital instructions?

Thank you!

If your soundbar supports LPCM, that’s all you need. Since Infuse is doing the decoding, nothing else in the chain needs to decode.

1 Like

See link below for the difference between PCM vs Bitstream settings.

Super helpful, thank you both.

My last question is what about post-processing modes like DTS Neural:X, can the receiver or soundbar apply the post-processing effects on 7.1 PCM?

How would the soundbar or receiver know that the output is PCM but DTS or PCM but Dolby, if it’s just sending the PCM signal? How would the receiver know what post-processing effect to apply if your receiver supports both DTS:X and Dolby Atmos (I understand Atmos and DTS:X won’t work with the infuse/appletv at this point).

Not sure I understand the question correctly but I’ll try to answer…

The receiver will know if its DTS or Dolby if the signal is set to bitstream, then the audio signal will be decoded by the receiver (you will see a DTS/Dolby signal on the receiver display). When the signal is set to PCM, the decoding is done at the source and therefore the receiver does not have to do any processing (it will show PCM on the display).

The format of the audio content is received by the player. Depending on if the player is set to passthrough the original audio and let the your receiver process the audio. If your player is set to LPCM then the player will do the decoding/processing of whatever format is received (DD,DD+,DTS,TRuHD et cetera) and send that to your receiver as LPCM and the receiver wont do any processing and send it on out to your speakers. if the player is set to passthrough the player wont touch the audio format and let your receiver do the processing and send to your speakers. If the player doesn’t know what audio formats your receiver can handle and it sends a format of audio to your receiver it cannot process you will not get the sound you expect.

That’s up to you on what up-mixing you want to apply, if any. Devices that support Atmos will be able to up-mix to Dolby Surround, and devices that support DTS:X will be able to up-mix to DTS Neural:X. If your device supports both (like my Denon) then you can choose which one you want. Soundbars will generally do this automatically and not give you an option.

I generally use DTS Neural:X.

Got it yeah that’s my understanding. Just wanted to make sure the receiver or Soundbar is smart enough and or capable to upmix 7.1 pcm

I have two questions: when Infuse decodes DTS to LPMC can I hear a difference between the original DTS track or the LPCM decoded track? If I can’t hear any difference I will buy an Apple TV 4K. Secondly ; why does Apple not want passthrough?

You shouldn’t hear any difference in audio quality. Your Apple TV is doing the deciding instead of your receiver. You might hear a difference if your receiver does weird stuff with audio… mostly when adding post processing effects such as Dolby or DTS up converting.

It’s assumed Apple doesn’t do pass through because of Siri integration and menus. Doing PCM allows Apple to add sound effects into the audio mix (menu clicks, voice over, etc).

Thank You for Your answer. I really have doubts and was thinking of a Nvidia Shield which has passthrough but I have an Apple eco system. All depends on good DTS decoding such as in Gravity

If you’re going to be doing Netflix, Hulu and other streaming services also then the AppleTV 4K is a great buy however if all you want is a top notch player to play back rips and downloaded media i’d look at other solutions such as the Vero 4K+

Thank You for Your answer; it remains difficult however. Apple TV 4K does provide Apple’s own + streaming, the VERO+ can only play files and the best is NVIDIA ( most powerful) but has no Apple TV+ streaming. Choices, choices…

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