How to control separate channels in digital ouput? (RPI and Vero)


First of all thanks a lot for this awesome open source project. I have been using OSMC for a few years and now I ran into a problem.

I have got a RPI (the first one, model B). The thing is that I bought a new TV with a soundbar, and they are connected through HDMI, and controlling everything from the TV remote is just fantastic, integration between devices is just magnificent.

Now my problem is that in films I hear voices really dim, I really find this annoying. But sadly and after reading about this, it seems that the problem is mostly how sound in movies is mixed.

The solution seems pretty simple though. Since in digital audio dialog and voices come from the central channel, I just need to make it louder.

Now if I check alsamixer in the OSMC from my RPI there is only one channel (PCM). I tested with another card I use in linux (Aureon HD 8.0), and now his one shows all channels available, 7.1 in this case. But now the problem is that optical output doesn’t work with soundbar for some reason. OSMC shows the output SPDIF for this card but I get no sound from that port.

Even if that worked I would like to use HDMI output for the sound. This way I would still be able to manage everything from the same remote.

Which leads me to the next question. Will a hardware with a better soundcard solve my problem, I’m thinking in a Vero 4K, will alsamixer allow me to manage channels separately and this will have effect on the HDMI output?

So as a summary and as the title says, I’m looking for a way to manage the volume of every channel for the digital output.

Is this even possible?

Thanks for the help.

I think the ‘Boost Centre Channel on Downmix’ option will do what you want. This can be configured in Settings -> Audio.

Thanks for your answer. Downmixing is sort of a workaround, but some comments:

Do any of this options matter when using HDMI? Because I set downmixing and set boost center channel to 30 and if there is any difference it is unnoticeable. Furthermore, I still hear dialog only from center channel, I expect it to hear from side sepakers as if I was using an analogic input.

Still I think this is a kludge, in the sense that I have got a set with 3.1 channels and with the downmixing I don’t take any advantage from it.

What about DSP plugins? What are they useful for?

Yes – they matter when not using passthrough.

Do you have passthrough enabled?
Disabling passthrough, setting speaker output to 2.1 and enabling boost center channel on downmix should suffice.

DSP plugins are not working in Kodi v17 / Krypton.
They will work in Kodi v18

I swear by god that I have got passthrough disabled, and output is set to 2.1. And still stereo downmix, and boost centre channel makes no difference, I mean even 6 or 9 DB should make a huge difference, am I wrong?

Besides I checked that the option volume amplification does nothing either. Both problems may be related?

Can you post a debug log?


Sure, I have got ssh and web access.

Can you point me to what files I must upload? Do you want me to run anything before getting them, like enabling disabling stereo downmix to generate such logs?


Thanks a lot for that link.

I enabled debug. Rebooted osmc. And then disabled and enabled stereo downmix, opened a file (dts 5.1) disabled passthrough, made sure that syereo downmix was enabled. And played with volume amplification.

Then uploaded logs. And got this link.

Man that’s a neat way to upload info. I usually work with big companies’s support and uploading files to them is a pain. And I’m talking about IBM, Cisco, Imperva …


I checked and boost center volume should work with omxplayer and not just dvdplayer.

Perhaps @popcornmix has some clues.

There’s an EQ, but limited userspace functionality at the moment. It’s not controllable via something like alsamixer.


Just to add some more info. I tested connecting my tablet to the same audio rig, and run kodi 17.3.

I can clearly see the difference in volume amplification. Sadly, I can’t find stereo downmix option in this version.

I wanted to ask also if is there any open source videos suited to test this kind of things. I mean something with a stable output from all channels, not any kind film (I guess big buck bunny is the obvious answer), more like a test environment, don’t know if I’m being clear.

I also wanted to ask what is the expected difference between boost central channel 0 and 30, I mean, it is supposed to be a subtle difference or at maximum level it must become an absolute aberration?