Audio passthrough - not quite what is seems

[kdp99]

I have had real problems getting 5.1 audio form the puck, which are documented here on other threads, but have found the issue is with the puck passthrough setting.

As the name suggests pass through sound just send the audio bitstream on unaltered to the TV, AV amp etc. I proved this is NOT the case by changing the system that the puck sends the audio to and with the same broadcast getting different audio streams (5.1 in one case 2.0 in another).

The the puck is trying to do something to the audio it sends via HDMI based on what it is sending to.

I think it it can't work out what it is sending the audio to, it reverts to 2.0. By forcing the output to DD+ 5.1 rather than pass through it gets round this.

I also suspect that there is another HDMI issue with the puck, as with HDMI control off, and the puck powered off, my TV will sometimes change tos HDMI1 (the puck input), of its own accord. I think others have this issue. Luckily I have a universal remote with macros which means this is not a serious issue.

[Nigelb1972]

Haven't had this issue at all. Our puck is set to Passthrough, the eARC on the TV is set to Passthrough and all the decoding is done by our Sony soundbar. 

[kdp99]

I think the issue only arrises if the puck does not 'understand' the system ut is sending audio to. In my case it did not understand so went to 2.0. If it 'understands' your you shoulf be OK.

Its still not pass through though !

[Exiled-in-HH]

@kdp99  what are the device models in your investigation?

[Nigelb1972]

Well it seems to be passing through the raw audio as my soundbar will happily swap between audio types depending on what is being broadcast. It'll swap between 5.1, 2.0, Atmos etc quite happily, even during commercial breaks. 

[Mister_Dalek]

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@kdp99 wrote:

I also suspect that there is another HDMI issue with the puck, as with HDMI control off, and the puck powered off, my TV will sometimes change tos HDMI1 (the puck input), of its own accord. I think others have this issue. Luckily I have a universal remote with macros which means this is not a serious issue.

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A CEC blocker will stop this. I had to get one for my puck as they do indeed send out spurious CEC commands, even in standby, which can affect and interfere with other A/V hardware. 

Both the Pioneer and Denon AVRs I used were affected by it, preventing any other devices connected to them from being controlled via CEC.

I got rid of the puck in the end. Problem solved. 

[CoffeeDrinker]

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@kdp99 wrote:

I think the issue only arrises if the puck does not 'understand' the system ut is sending audio to. In my case it did not understand so went to 2.0. If it 'understands' your you shoulf be OK.

Its still not pass through though !

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Think of it as 'active passthrough' rather than 'passive passthrough'.

If the sound device upstream is not capable of decoding a Dolby Digital Plus bitstream (capable of Atmos, 7.1  5.1, and 2.0), the puck actively understands this and should downgrade to the older Dolby Digital codec (capable of 5.1 & 2.0). If that fails, it should finally step down to PCM stereo (2.0).

If the puck were to passively output DD+ regardless of the upstream sound device's ability to decode it, the result would either be silence or a blast of unintelligible static if the upstream device cannot handle DD_+ (as what used to happen when an older DVD player was set to output DTS via optical into an AV receiver that didn't understand DTS).

The puck does output an untouched audio bitstream, but only after determining that the upstream audio device can handle the untouched codec/bitstream. This should happen gracefully, negotiating from DD+ to DD 5.1 to DD 2.,0 to PCM 2.0. As you've found though, depending of device manufacturers and combinations, this isn't always the case.

Good to hear you've got your audio working though 👍