Hi to All and a Happy New Year to you,

I used some downtime over the holiday to look at the sound performance of my Mut@nt HD51 4k, because I couldn't get 5.1 surround sound coming out of it. I still can't.

This is my connection setup with my Mut@nt HD51 fitted with two Freeview receivers and currently running OpenVix-5.1.007.

Mut@ant ==> HDMI ==> Sony TV <==> HDMI ARC <==> Yamaha AVR ==> 5.1-Speakers

The Mut@ant is connected to Sony TV XE9005 using a HDMI cable and Sony in turn is connected over HDMI ARC to a Yamaha AVR. The Yamaha, which is capable of processing mpeg4-AAC, receives the PVR audio over HDMI ARC, while the TV displays the picture.

Without the Mut@ant running, when the Sony TV is receiving a Freeview HD channel itself which shows up as 'Audio AAC 3/2.1' on its info panel, the Yamaha is able to output 5.1 surround sound.

When the Mut@ant is switched on and is also receiving the same Freeview transmission, only a stereo sound comes out of the Yamaha.

I've also tried plugging in the HDMI from the Mut@ant directly into the Yamaha, but it made no difference. The sound transmitted from the Mut@ant over HDMI is always stereo.

Settings on Mut@ant:

I tried playing with the Audio settings available in Mut@ant's GUI. Under Automatic Language settings, I set it up to prefer AC3 and AC3+, but I expect these will only have an effect with satellite receivers. When I press the Audio button on the remote I see that the first of the two 'AAC-HE' English audio is selected - the second being the Audio Description [AD] for visually impaired. The 'Audio Channel' in the same menu is set to 'Stereo'. Switching the 'Audio Channel' between stereo/left/right makes no difference, nor does switching On the AC3 and DTS settings below.

AC3 Downmix Off
DTS Downmix Off
Audio Channel Stereo

I've also checked the streams captured in a Mut@ant .ts recording, which the TV was able to play with 5.1 surround sound. The recording contains two audio streams, the first of which is a 5.1 track surround sound stream and the second a stereo stream for [AD].
Code:
   Stream #0:1[0x66](eng): Audio: aac_latm (LC) ([17][0][0][0] / 0x0011), 48000 Hz, 5.1, fltp
    Stream #0:2[0x6a](eng): Audio: aac_latm (HE-AACv2) ([17][0][0][0] / 0x0011), 48000 Hz, stereo, fltp (visual impaired)
So the sound is captured with 5.1 audio tracks when available in the transmission, but will not be played out as such. Somehow it seems to be downmixed to stereo and I haven't found a way to disable this. I've looked at alsamixer, but I can't find a setting to enable 5.1 audio tracks there. This is alsa's stored settings:
Code:
state.bcm {
	control.1 {
		iface MIXER
		name 'Master Playback Volume'
		value.0 31
		value.1 31
		comment {
			access 'read write'
			type INTEGER
			count 2
			range '0 - 63'
		}
	}

	control.2 {
		iface MIXER
		name 'PCM Playback Volume'
		value.0 8388608
		value.1 8388608
		comment {
			access 'read write'
			type INTEGER
			count 2
			range '0 - 16777215'
		}
	}
	control.3 {
		iface MIXER
		name 'Decoder Audio'
		value true
		comment {
			access 'read write'
			type BOOLEAN
			count 1
		}
	}
}
How can I enable live and recorded 5.1 surround sound to be played out of the Mut@ant?