5.1PCM being converted to 7.1PCM - how to stop this?


#1

My Vero 4K is connected to a 7.1-capable receiver. All passthrough formats for Dolby/DTS etc work perfectly. However, a small number of titles have 5.1PCM audio. No matter what settings I use for Number of Channels/Output configuration, my receiver always reports that the incoming signal is 7.1 when I play 5.1PCM mkv files.

I don’t want the Vero to be doing any channel mapping of any kind, as my receiver has to do some of that anyway. I want all audio to be passthrough but cannot find a setting for “native” PCM (feels like an omission in terms of the GUI). I tried setting Output Configuration to “fixed” and channels = 5.1, but that did not work and also broke passthrough for Dolby/DTS. Any suggestions at all?


#2

5.1 LPCM output isn’t possible. You can use 7.1 or 2 ch output for PCM. If you need 5.1, use passthrough. If the source can’t be passed through, then you won’t hear a difference. A good source will be encoded in a format that can be passed through.

Sam


#3

why is that? I just reconnected my LibreELEC Pi and that outputs 5.1 PCM just fine for 5.1 sources with the maximum number of channels set to 7.1 in Kodi. So the Pi/LE figures it out.

Er, there isn’t a passthrough option for native PCM material.

Examples of blu-rays I own that have 5.1 PCM audio:
Pirates of the Caribbean 1-3
Several Harry Potter’s
Casino Royale
Deja Vu

I don’t think it’s unreasonable to expect the Vero to be able to passthrough 5.1PCM natively ?


#4

At the moment, the Vero 4k can only open 2 or 8 audio sinks to output PCM audio via HDMI. So, stereo will be ouput as 2 channel PCM, but every PCM audio file with more than 2 channels will be ouput as 8 channel PCM via HDMI. The remaining channels that are not filled by information from the played audio file (e.g. with a 5.1 PCM audio file - ergo 6 PCM channels - there are 2 channels left to be filled for 8 channels to be output) will be filled with blank channels containing no audio information.

See the attached image as well:

Clipboard01

This is, of course, not awesome for dedicated 7.1 setups where the AVR can’t upmix 5.1 to 7.1 because it thinks there’s already a 7.1 signal coming in - which obviously contains 2 blanks channels. But the AVR can’t and won’t know that. So, especially setups which do upmixing of some sorts (to 7.1 dedicated speaker channels or 3D audio setups using 3D upmixers like DTS Neural:X e.g.) are affected negatively by this…

The whole issue - including all the implications for whatever scenarios are out there - has been discussed in the context of some PCM channel mapping not working before (which is fixed now), but Sam couldn’t raise much hope of this being changed any time soon.
But @ac16161, others - including me - have been asking for this, too. It’s something that has been asked for before and Sam is aware of it, I think. Maybe we’ll see some changes some day.


#5

Thanks for posting such detailed background. I’m a little disappointed, as I had assumed that the Vero 4K would support direct passthrough of PCM as well as HD bitstreaming. I can see how in some set-ups the lack of 5.1 PCM passthrough could be annoying. 5.1 PCM content is undoubtedly in the minority, but it’s hardly rare, so feels like a gap.


#6

There’s still a few issues with the Vero4, but at least we know that Sam is listening to his customer’s feedback and trying his best to issue fixes and upgrades on a monthly basis. I don’t think there’s many (if any) other products out there that get the same kind of support.
We just need to show a bit of patience. IMHO, the Vero4 is already the best media player available.


#7

It definitely is! And the support is outstanding… :star_struck:

Last I heard something on this PCM audio matter from @sam_nazarko is about a month ago. But I doubt that there’re any news on some sort of a solution for this yet, are there?


#8

I agree that overall the Vero 4K probably is the best device out there of its type, and I have appreciated the prompt support on this forum. But having come from a LE Pi, I was just a little surprised that something as mundane as 5.1 PCM passthrough is not currently supported. I can imagine there’s quite a wish-list of requests that Sam is attending to, and look forward to seeing what’s next for the Vero.


#9

Thanks for the kind words. As always – there’s never a shortage of bugs or things to address.

The Raspberry Pi is a different piece of hardware. You can get LPCM 7.1, but conversely can’t bitstream HD audio formats.

You may get away with enabling AC3 transcoding and setting the number of channels to two. It depends on how good your ears are.

Sam


#10

That’s a workaround to get PCM audio to the AVR in some way with source channel layout (at least for 5.1). But of course, this would defeat the purpose of the Vero 4k as a perfect device to play surround audio files bit-perfect (up to 7.1 24bit 192kHz which the RPi can’t do) without any transcoding or altering of the file…


#11

For anyone that converts 5.1 TrueHD or DTS-HD MA to FLAC to save space on rips, this will be an issue (since FLAC is decoded and sent as PCM). A lot of people do this, as it causes no loss of quality, but does save space.


#12

To my understanding, Sam knows that there’s demand for this and he’d be willing to look into it, but it also depends highly on the SoC’s vendor - AMLogic - to implement ways to open basically any amount of audio sinks between 2 and 8. This is not just something as trivial as it might seem…


#13

I think 2, 6, and 8 are all you really need. There is virtually no content with 3, 4, or 5 channels that would need to be sent as PCM with those exact channel counts.

L+R+C+LFE+LS+RS+CS could be sent as 8 channels with LSR and RSR each dups of CS.
L+R+C+LS+RS could be sent as 6 channels with a silent LFE.
L+R+LS+RS (quad surround) could be sent as 6 or 8 channels, since you don’t really want any channel munging done by an AVR, anyway.

I think I have exactly one movie (out of 750) that has 3 discrete channels (L+R+C), and one with 4 (L+R+C+S), and both are 640Kbps AC-3, so the receiver will sort it out.


#14

Yes, maybe it would be an implementation which would add one more mode: 6 audio sinks open. Or maybe it would allow all scenarios. Maybe, maybe.

Still, it’s nowhere near a discussion about how many channels would be needed or whether more than 2, 6 and 8 sinks are necessary or difficult to do. Sam couldn’t raise hopes for this to come soon at all when he last gave a heads-up on this…

But I don’t want to speak too much for him. If I’m wrong about this or if something has come up, please correct me, @sam_nazarko :slightly_smiling_face:

It’s not so much about movies for me, but music. I have only this device which can easily output surround PCM audio in a bit-perfect fashion via HDMI. And it has access to my music library. 5.1 PCM music files do exist quite a lot especially when it comes to SACD content and classical/jazz music. In the field of jazz music, there do exist 3 channel files. But you’re right, it’s not really common.


#15

Correct. 2,6,8 will tick almost all boxes.

There might be a dirty hack that can be achieved – but I haven’t had a chance to yet explore this further. It may also trip up some AVRs, so needs investigating.


#16

Let us know as soon as there’s anything, even something very basic and rough to test. I’d be happy to test :+1:t2:


#17

I’ve been doing some more thinking on this, and I now think it should really be a low priority.

First, we have to assume that the user has equipment that can understand 7.1. If they have a really old AVR that literally can’t conceive of more than 5.1 channels, then that’s a big issue, but the number of people with a setup like that and needing a device like the Vero 4K for the video end is very small, so I think we can ignore them.

For standard 5.1 (L+R+C+LFE+LS+RS) PCM (or PCM-out audio like FLAC or AAC) in the source video, there are effectively 3 cases in the user playback equipment:

  1. Much less than 5.1 speaker setup (i.e., not just missing a subwoofer). OSMC shouldn’t care about this, because such setups should have the Vero 4K set to 2-channel output, or should let the equipment deal with the fairly complicated re-mapping of channels.

  2. 7.1 or greater speaker setup. Sending 5.1 as 7.1 with silent LSR+RSR will only affect the ability of technologies like ProLogic IIx from expanding the content to get sound from all speakers. No sound from the mix on the source will be lost…there will just be silent rear (and possibly 3-D) speakers. It would be the same as listening with just a 5.1 speaker setup.

  3. 5.1 speaker setup. I think this is actually the biggest issue, as sound will be lost, since the downmix from 7.1 source to 5.1 speakers will mix LSS+LSR source to output to LS speaker. Since LSR will always be silent, this will mean that the LS output will be too quiet on movies with 5.1 channels, and OK on movies with actual content in the rear speakers.

But, I again don’t see a lot of people who want a device like the Vero 4K only having 5.1 setups. Sure, you could see much lower configs, like soundbars in bedrooms, but anybody with a Vero 4K and at least 5.1 speakers probably has the full 7.1 (or greater) setup. So, almost nobody will lose anything of significance with the current way sound is being output.

So, my vote again is to put this into a “nice to have” priority, but definitely things like HDR->SDR tweaks should be more important.


#18

Honestly, you’re kind of missing the point here IMHO. :wink: It’ll not “only affect the ability of technologies like ProLogic IIx” - don’t like the only here :yum:… We’re in the age of Dolby Atmos and DTS:X which means all new AVRs (above the absolute entry level) can handle 7.1 channel input (and therefore downmixing) and they’re always equipped with upmixers like Dolby Surround and DTS Neural:X (and some even with AURO Auromatic). And keep in mind: one of the key features of the Vero 4k is HD audio bistreaming which is needed especially for Atmos and DTS:X (the combination with a newer 3D audio AVR is literally what the Vero 4k is predestined for).

So, if you have a dedicated 7.1 speaker setup with side surround speakers, playing back a 5.1 PCM audio track with 2 blank surround back channels will mean this: You’ll have sound from the sides, but none from the back. This is not only somewhat less than perfect, but it destroys any form of surround sound atmosphere. There’s simply no sound from the back and the AVR can’t do anything about it. At the moment surround PCM audio playback (most surround audio files have “just” 5.1 channels) on the Vero 4k is more or less non-usable… This is quite a big issue for 7.1 speaker setups.

I totally agree on this and your first point. If you add those together, it’s basically affecting users with 5.1 AND 7.1 speaker setups (and 3D setups on top of those) which isn’t a small group, I’d presume. :wink:

But in the end, we don’t have to argue too much about the downsides and the necessity of a fix as there’s no easy way to fix it yet and I’m guessing it’s not on top of Sam’s to-do list anyway…


#19

Agreed - this is the one thing that stops the Vero4k being perfect for me. It means I have had to go back to using my BD player and physical discs as they sound so much better. Quite a disappointment :frowning_face:

I am no expert but couldn’t someone add a hack that takes the 5.1 track and literally strips the 2 empty channels so that any AVR’s that are >5.1 only see the actual 5.1 channels with sound.
I don’t understand how NULL channels are still outputting anything to confuse the AVR.


#20

The subset of AVR owners that have a 7.1 system that does not accept 7.1 bitstream formats is probably very, very small.