5.1 track AAC surround sound audio with Freeview receivers

[Mickkie]

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].

   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:

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?

[twol]

You might want to look at this and talk to Birdman/Fat-Tony for more Info.....
http://www.world-of-satellite.com/sh...-HDMI-ARC-help

[Mickkie]

Thanks twol!

I will post in that thread, but TBH I don't think this is either an HDMI cable or port problem. All my HDMI cables are of high speed 18Gbps 4K capable spec. Something else must be amiss here. The OpenVIX interface does not offer anything other than stereo in the audio channels, where I assume it should also show 5.1/6ch audio output.

[twol]

Thanks twol!

I will post in that thread, but TBH I don't think this is either an HDMI cable or port problem. All my HDMI cables are of high speed 18Gbps 4K capable spec. Something else must be amiss here. The OpenVIX interface does not offer anything other than stereo in the audio channels, where I assume it should also show 5.1/6ch audio output.

Not sure you read it all ..... „
What ARC can not do is pass HD audio such as PCM 5.1/7.1, TrueHD, DTS-HD MA, this is a limitation of HDCP and bandwidth, in such a case you need to connect directly to an AVR via HDMI (or you can use multi channel analogue for PCM only).„

My HD51 (& Giga4K) quite happily pass 5.1 thru my Onkyo receivers to the loudspeakers..... so not a HD51 issue

[Mickkie]

Thank you for your help twol,

My HD51 (& Giga4K) quite happily pass 5.1 thru my Onkyo receivers to the loudspeakers..... so not a HD51 issue

I'm sorry for being dense ... I have connected the Mut@ant HD51 with a HDMI cable directly to one of the AVR input ports again. The audio is played out of the AVR, but it does not come out as 5.1, only stereo. The TV is connected to the AVR via HDMI ARC - just to transfer the video signal. Am I supposed to do away with ARC ports completely and use a normal HDMI port between the TV and the Yamaha?

What "Audio Channel" do you see displayed when you click on the Audio button on the remote? What other audio settings are you using?

[Mickkie]

Hmm ... further investigation revealed:

1. The Sony TV is pushing DD 3/2/0.1 channels through the HDMI ARC port to the Yamaha AVR. So it appears the Sony TV is transcoding AAC 5.1 audio to Dolby and sends this down the HDMI ARC cable.

2. No matter what I settings I tried on the Mut@nt, the Yamaha AVR shows it receives PCM 2/0/--- from it, when the Mut@nt is plugged directly into the Yamaha with an HDMI cable.

Is there some setting on the Mut@ant I can try to alter to make it push out 5.1 audio?

[Joe_90]

I think the mutant can either pass the AAC audio direct or transcode it. Are you sure the Yamaha receiver can handle AAC audio? Most AV amps cannot handle AAC. You are using 5.1, AAC and AC3 interchangeably in your initial post. Dolby digital and AAC are different codecs. Freesat uses Dolby digital AC3 to carry 5.1 audio information. Most audio systems can handle this. Freeview uses AAC which most audio systems cannot handle. You either have to transcode to AC3 or to stereo (2.0) unless you have a device capable of handling AAC.

[Mickkie]

I think the mutant can either pass the AAC audio direct or transcode it.

Ah! Where can I select what it is transcoded to?

Are you sure the Yamaha receiver can handle AAC audio? Most AV amps cannot handle AAC.

Well, the Yamaha RX-V583 says among other audio formats it can decode MPEG-4 AAC. However, digging deeper in its manual it does not mention AAC over HDMI. It states HDMI is HDCP compliant. For file audio formats over USB/PC/NAS I can I see it mentions MPEG-4 AAC, but only with 2 channel support. So perhaps it won't decode AAC 5.1 over HDMI too?

You are using 5.1, AAC and AC3 interchangeably in your initial post.

Not really, I only mentioned the two Dolby related audio settings available in OpenVIX and said these had no effect in the output.

You either have to transcode to AC3 or to stereo (2.0) unless you have a device capable of handling AAC.

OKie dOKie, where in the Mut@ant settings can I select the audio to be transcoded from AAC to AC3 (the Yamaha can play all flavours of Dolby)?

[Mickkie]

I found the definitive and detailed spec for the AVR. Alas, it will *not* play AAC at all it seems, at least not over HDMI:

HDMI Features:
 • 4K UltraHD Video (include 4K/60, 50Hz 10/12bit), 3D Video, ARC (Audio Return Channel), HDMI Control (CEC),
 Auto Lip Sync, Deep Color, “x.v.Color”, HD audio playback, Selectable HDMI input in HDMI standby mode,
 21:9 Aspect Ratio, BT.2020 Colorimetry, HDR Compatible 

Video Format
[snip ...]

Audio Format
 • Dolby Atmos
 • Dolby TrueHD
 • Dolby Digital Plus
 • Dolby Digital
 • DTS:X
 • DTS-HD Master Audio
 • DTS-HD High Resolution Audio
 • DTS Express
 • DTS
 • DSD 2-ch to 6-ch
 • PCM 2-ch to 8-ch (Max. 192 kHz/24-bit)

 Content Protection: HDCP 2.2 compatible

A real Who-is-Who of proprietary codecs in there.

Nevertheless, if I read the above correctly, the Yamaha AVR should be able to play multichannel PCM, or Dolby audio over HDMI. Therefore with a better understanding of what the AVR can do, please let me reformulate my question:

How can I configure the Mut@ant to output over HDMI either decoded multichannel PCM (not just stereo), or multichannel Dolby?

[twol]

If its a channel (like BBC1 HD) that outputs AC3, providing you don‘t down grade it to stereo in setup/audio, it outputs AC3 on hdmi. PCM, I am not so sure about it might just be 2 channel stereo.

[Mickkie]

Thanks again twol,

If its a channel (like BBC1 HD) that outputs AC3,

Are you sure it does? Please note I don't have satellite receivers, only Freeview. The Freeview transmission is AAC 5.1, so the Mut@ant will need to transcode it to AC3 (or decode it to multichannel PCM). I have not found a setting to implement either.

... providing you don‘t down grade it to stereo in setup/audio, it outputs AC3 on hdmi.

I have selected to NOT downmix AC3/DTS to stereo, under Setup=>Audio & Video=>Settings, but still the AVR receives a PCM stereo signal.

Are there any other settings/plugins/configuration files I could try to tweak for this purpose?

[ccs]

Long discussion a while ago.....

http://www.world-of-satellite.com/sh...0895-Dolby-5-1

[twol]

Thanks again twol,
Are you sure it does? Please note I don't have satellite receivers, only Freeview. The Freeview transmission is AAC 5.1, so the Mut@ant will need to transcode it to AC3 (or decode it to multichannel PCM). I have not found a setting to implement either.

I have selected to NOT downmix AC3/DTS to stereo, under Setup=>Audio & Video=>Settings, but still the AVR receives a PCM stereo signal.

Are there any other settings/plugins/configuration files I could try to tweak for this purpose?

Yes, I wasn‘t thinking when I responded as I have Sat tuners.... sorry
I wonder what comes out of the optical? I have tried googling but didn‘t find anything useful.... but if you can somehow hook it into the setup, it might do the job

[Joe_90]

@Mickkie - I think that perhaps the mutant HD51 does not have the ability to transcode the AAC 5.1 audio to AC3 for your AV amp and that is why you are getting 2.0. My GB Quad Plus has a setting to transcode AAC to Dolby AC3 (which is wasted on me as I can't receive UK Freeview transmissions), but I don't see a similar setting on the mutant. Very few AV amps actually support native AAC - most are Dolby or DTS with the ability to support the HD audio streams on the higher-spec boxes.

[Mickkie]

@Mickkie - I think that perhaps the mutant HD51 does not have the ability to transcode the AAC 5.1 audio to AC3 for your AV amp and that is why you are getting 2.0.

Thank you fat-tony, I suspect you are right. I don't know if this is a hardware limitation of the Mut@ant, or just that no dev found it interesting to write some code to do this yet. Even if the hardware will struggle to transcode the audio in real time and keep video and audio in sync., it can be done on recordings. On my laptop I converted the AAC audio of an hour long recording to AC3, in less than a minute and a half. I haven't yet tried to do it on the Mut@ant, but this is the stanza I used:

ffmpeg -i 20171210\ 1959\ -\ BBC\ ONE\ HD\ -\ Blue\ Planet\ II.ts -codec:v copy -codec:a ac3 -b:a 384k -ac 6 /data/20171210\ 1959\ -\ BBC\ ONE\ HD\ -\ Blue\ Planet\ II.ts

The mapping of the surround sound channels appeared to be correct between the two codecs; I'll run some more tests when I get the time to check it more thoroughly.

Meanwhile, I also ran a test with a Kodi box connected to the Yamaha AVR over HDMI. Although the .ts file sent to the AVR contained audio in AAC 5.1, the AVR once more reported receiving only a PCM stereo signal over the HDMI port and played it over 2 channels. I suspect that the AVR downmixes the 6 channel audio stream and plays it as a 2 channel stereo. Perhaps Yamaha have decided in their wisdom AAC is only useful to their customers as a stereo output, which is the typical use case of iPhone/Android users.

I may write a cron-job to scan for recordings with surround sound and then convert them to AC3 overnight, when the box is not in use, unless anyone can advise of a plugin which already does the same?

PS. Thank you twol, fat-tony and css! Following your pointers and links has proven educational for me and saved me a lot of head scratching.