Sky Stream - PCM from iPlayer etc received via passthrough as a Dolby signal?

[POckelford]

I have the Sky Stream in passthrough mode to a capable Denon AVR. Streaming live TV it sends a 2 channel PCM signal which I can apply DTS Neural X to and it sounds great. Streaming from iPlayer, Channel4 (or any app without 5.1+) it sends a 2 channel PCM signal that mh AVR will only let me listen to in Stereo, Dolby Surround, or Multi-Channel Stereo. Even in Pure Direct mode which cuts all processing it still plays the 2 channel PCM as a Dolby Surround upmiced 5.1 - which sounds awful as the dialogue bleeds into the surround channels.

Does Sky add some sort of Dolby wrapper to the apps' PCM? Other devices output pure PCM that can have Neural X applied (and it's so much better). 

Oddly, setting the Stream to DD+ allows my receiver to use Neural X - but I'm guessing that's because the Stream has already decided the audio - rather defeating the purpose of the receiver. 

It's very frustrating!

[POckelford]

decided should read decoded. Does this forum not allow edits?

[CoffeeDrinker]

Will check this evening and see if I get the same result with my Denon X3500H AVR with Stream & iPlayer.

The PCM format dates from the early 80s at the latest; there is nothing in the specification that allows a Dolby wrapper or similar. With a PCM stereo feed over HDMI or optical/coaxial and direct mode on the AVR, playback should only happen via the front L & R speakers as you'd expect if you hooked up a CD player. Alternatively you should be able to manually select either Dolby Surround (the newer version that upmixes to 5.1/7.1/above, not the original pre Pro-:Logic Dolby Surround) or DTS Neural X (which does DTS' equivalent of the Dolby Surround upmixer).

[POckelford]

Any luck replicating? I'm using an x4700 and watching iPlayer, 4, or just sitting on any app menu with now sound, with the stream puck set to passthrough, the only options I get are 1. Stereo 2. Dolby Surround 3. Multichannel Stereo.

If I press info on the AVR remote it tells me the audio input signal is 2 channel PCM.

As mentioned I'd love to use (and I can't find any reason for not being able to) the Neural X upmixing, as Dolby Surround manages to mix dialogue into the surround channels. But... The Denon simply doesn't allow it with this.

When the input signal is DD+ I actually do the full list of eight options including DTS Neural X.

I just can't make sense of it.

Just to register on a side note that I suffer from the DD+ drop out as frequently as most others here. Twice in the 48 minute Netflix show I was watching this evening. Three times watching Apple TV+ yesterday... It's infuriating.

[GD1]

@POckelford  Have you tried audio in Auto rather than pass through?

[POckelford]

Hi - Auto gives me the same 2ch PCM signal from non-DD+ sources, and the AVR gives me the same three sound options, sadly. 

Out of interest, how does Auto handle DD+ signals? Still pass to the AVR or does the puck decode it first?

[GD1]

@POckelford  I would need to see how my AV receiver handles BBC iPlayer sound, is there a specific program on the iPlayer?

I can report back my findings tomorrow.

[POckelford]

Thanks. It's everything on iPlayer - standard or UHD all has the same audio - for an exact match I was testing it with W1A S3E2.

It's also everything on 4, ITV, etc, and sitting in the menu on Disney+ or Netflix, etc... Essentially, whatever is happening to the PCM signal from the puck in passthrough mode is somehow limiting the options on the Denon. As mentioned, all DD+ signals from the puck (in passthrough or otherwise) can have many more of the Denon's sound options applied. 

The ONLY way I can get around this is setting the puck to output PCM Stereo - with this PCM 2ch signal, DTS Neural X is an option... But I obviously lose all DD+ signals... So what's the difference between PCM sent by passthrough, and PCM sent by PCM Stereo? I wouldn't have thought anything - but my AVR can certainly find a. Difference! 

[GD1]

@POckelford  Doing a quick test with Dr WHo 2005 series,  in Passthru my Sony 7.1 Amp gives me the following sound options

This happens on all Sound setting on the puck

2 Chan Stereo

Multi Chan Stereo

AFD

Dolby Surround

Neural:X

It may just be the difeence in Amps,  so I can't mirror the sound issues you get.

[POckelford]

Thank you testing it. I wonder if anyone from Sky knows the specs of the PCM output while in passthrough, and why that differs to the PCM in PCM Stereo mode.

Without that I won't be able to ask Denon why the incoming signal is treated differently.

Thanks!