Dolby 5.1+ Sound issues

I’ve got a strange, intermittent problem with audio using video files with Dolby 5.1+ sound. This happens for a time, then reverts back to the previous behaviour. It started after the November update, but not straight after. First, my set-up.

My Vero 4k+ is connected directly to my aging LG 2.1 sound bar (NB3530A) using an optical cable. I’ve set it up according the OSMC’s Audio H/W and S/W Configuration document., Section 2.1.1. I’ve enabled pass through for vanilla AC3 and DTS, and enabled AC3 transcoding.

It’s worked fine for months that way. I can adjust the volume using the Vero remote. The problem is that recently and randomly after starting to play a video with the Dolby sound, it would be loud, the Vero’s volume control would be locked. I can adjust the volume using the sound bar’s volume control, but not the Vero’s. This prompts me to reboot and play with the settings. Nothing I can put my finger on cures the problem, it magically goes away, and works as before.

I previously tried to get a log capture, but after setting up the log capture and rebooting twice the problem went away. FYI, rebooting twice doesn’t always clear the issue. I will try to get a log the next time the problem surfaces. It’s working at the moment.

Note that other audio codecs, eg DTS, ACC, AC3 etc don’t have this issue. They work as before even when the problem manifests.

Any thoughts?

10 minutes after writing the post, the feature returns. Log link below.

Briefly, why are you transcoding AC3 (probably to PCM) when your receiver is AC3 capable ?

I checked the spec here NB3530A and it supports Dolby Digital (i.e. AC3) and DTS 5.1 but does not support EAC3 (Enhanced AC3) and DTS-HD.

There’s no need to transcode AC3 if the receiver is capable of supporting the format.

Try turning off AC3 transcoding.

Briefly, why are you transcoding AC3 (probably to PCM) when your receiver is AC3 capable ?

Because that’s what it says to do in the set-up document. Perhaps your observation is correct if the connection is HDMI? The sound bar is connected by S/PDIF optical cable. Perhaps the audio experts can clarify?

My (perhaps incorrect) reasoning is that setting up this way makes use of the three channels the sound bar is capable of?

Lastly, the reason why I posted this is because the system switches randomly to not being able to use the Vero volume control, admittedly a ‘first world problem’ as the sound quality doesn’t change. On reflection, this may have started after the last Vero update.

Sorry, did you try what I sugested ?

I noted the following in the wiki, in section 5, did you check your settings against these

When using the S/PDIF output of your OSMC device for audio

Go to Settings/System/Audio… Select the following settings (keep in mind to set the settings level to ‘Expert’ in the bottom left corner of the settings window to see all settings necessary) :

  • Audio device:
    • Vero 2, 4K/4K +: PCM or HDMI
    • Vero 1: S/PDIF
    • Raspberry Pi: your S/PDIF soundcard
  • Number of channels: 2.0 (S/PDIF only supports 2-channel LPCM)
  • Output configuration: Best match
  • Passthrough: enabled (on Raspberry Pi select Passthrough device: your S/PDIF soundcard)
  • DTS/AC3 passthrough: enabled
  • DTS-HD passthrough: disabled (only present on Vero 1 and Vero 4K/4K +)
  • TrueHD passthrough: disabled (only present on Vero 1 and Vero 4K/4K +)
  • E-AC3 passthrough: disabled
  • AC3 transcoding: enabled (enable this if you don’t want multi-channel LPCM and HD audio down-mixed to 2.0 LPCM, also see the explanation of AC3 transcoding a bit further down)

Just a suggestion, difficult for me to re-create the problem and test it, I would also try setting the defaults on the settings/System/Audio… page. And then set them all to your requirements once again. But then, I would be suprised if you have already tried this. Sorry I can t help further.


Thanks @thechrisgregory for your assistance. That’s exactly how it’s set up.

Interestingly, the fault has reverted to the original behaviour and I can now control volume through the Vero.

It’s annoying but not a show stopper.

Maybe it’s time for a new (HDMI) soundbar !

You’re probably right.

The volume control in this type of setup is adjusting how loud of a signal Kodi is sending out. The optical connection has no signaling for volume as part of its spec so Kodi can only control its side of the volume. As such the volume you hear is a function of both Kodi, and your soundbars volume. If Kodi’s volume is low and your soundbar is all the way up, then it will be low. If Kodi is all the way up but your soundbar is set at a low volume then it will be low. The way one would normally set this up is to turn Kodi to max volume and then turn the soundbar up to where it is as loud as you want it to get.

This may be a bit more complicated now as something in Kodi seems to have changed such that its volume gets reset back to 100% when it is rebooted. There is a fix to change this I found and outlined [here]

Things work a bit better with a HDMI connected soundbar as Kodi will switch over from controlling its volume via adjusted its output volume to directly controlling the volume on the soundbar itself via CEC. This also gives a bit of a gain in audio quality as you get a better S/N ratio outputting at full output from Kodi.

There is an additional complication to how you have your settings at the moment. Kodi will only adjust the volume of a PCM signal. If you have passthrough turned on for AC3 and DTS then anything with these particular codecs will only output at full volume from Kodi, period, full stop. When you are passing through these formats that are in the original files then adjusting Kodi’s volume should show up on the screen as an icon, but the volume doesn’t change as Kodi will not touch what is passing through. What the inconsistency your likely seeing is if your playing mp3, FLAC, AAC, PCM, DTS MA, eAC3, etc. then Kodi is converting them to PCM where it can control the volume, and then because of your settings it is then converting it to an AC3 file that then has modified volume.

With your hardware setup you need to just output stereo and turn off passthrough, or else give up on controlling volume from Kodi. If you wanted to enable passthrough in case you were getting better audio somehow, then the better way would be to use a universal remote that was controlling the volume on the soundbar directly.


Thanks for the detailed reply @darwindesign

Yes, I get that the Vero can’t control the volume of the sound bar via an optical cable. The unit I have does not have an HDMI input so I’m stuck with optical or analogue.

Probably time to upgrade.

I’m aware of the balancing act between the Vero and sound bar volume controls.

However …

If you have passthrough turned on for AC3 and DTS then anything with these particular codecs will only output at full volume from Kodi, period, full stop.

That’s the way you say it should behave, but I can assure you, it doesn’t. Most of the time, regardless of the audio codec, the volume can be controlled using the Vero remote. It’s only on random occasions with videos using Dolby 5.1 sound that the behaviour is as you describe. I’m not suggest you are wrong, but this is how my setup performs.

Perhaps there’s a bug either in the hardware or software? There’s probably not a lot of people out there using legacy sound bars so it’s not an issue for the majority of users.

As stated in previous posts, it’s only an annoyance. I like being able to control everything with one remote.

Perhaps @Chillbo or @grahamh can comment, as they are the authors of the instruction document I used to set up my equipment.

In the log you posted above was it not the case that volume control didn’t work playing Moon but it did for Moneyball?

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I think you’ve misunderstood what transcode AC3 does. It takes a PCM signal and converts it TO AC3. That’s so that multi-channel audio can be played back through TOSlink. @tony-r is right to have it turned on as that’s the only way he’s going to get multichannel DTS or flacs to use all his soundbar’s speakers.

If someone had a soundbar that was actually using the discrete channels for something. In this case I think it is highly unlikely that LG is defining its ‘point one’ to mean a LFE channel. I would imagine this is nothing other than just a stereo soundbar with a dedicated sub running from a fixed cutoff point. AC3 may have advantage if the processor is able to use the multichannel to get better results from night mode/dialog boost/etc, but that should probably be a big “IF” when your talking about an older model soundbar.

Ah yes, thanks for that - AC3 is a compression codec, PCM is uncompressed, so it follows that it must be converted to AC3 from PCM !

Yes, but that’s the errant behaviour. It changes at random. Most of the time I can control volume via the Vero remote regardless of the codec.

I can get a log of when it behaves the other way if that would help. Will try to do it tonight. (Adjust for the 10 time zones between us!)

Although it may seem random, I just don’t know how such a situation could exist within the parameters of how I understand, and have experienced, Kodi to act. You say that you have volume control with a plain AC3 track and I have never known this to be something that would work with this type of setup. I could see where someone may have something like an eAC3 track and then thinks that they have volume control with AC3, but as I tried to explain previously, there is a logical explanation where one would work with volume control and not the other. What I described also explains why ‘when this situation happens’ you get increased volume since it would be passing through the original unaltered soundtrack.

To @darwindesign @thechrisgregory and @grahamh , thanks for the feedback regarding my unusual problem.

I’ve ‘bitten the bullet’ and replaced my ancient sound bar with an HDMI version.

I can assure you that the problem was real. Whether it was something unique to my setup or some bug in the device, who knows?

Anyway, thanks again for the attention you gave to my issue. The issue is closed for me.

Merry Christmas Tony !