[mythtv-users] Raspberry Pi audio centre and sub swapped

David Hampton mythtv at love2code.net
Mon Nov 27 01:04:06 UTC 2017


On Sun, 2017-11-26 at 19:47 -0500, Peter Bennett wrote:
> 
> On 11/26/2017 05:03 PM, Andrew Wilkinson wrote:
> > Hi,
> > 
> > I recently tried to start watching the BBC's Blue Planet 2, but 
> > unfortunately I have a problem with the audio. It's broadcast in 6 
> > channel AAC which my onkyo can't decode, so for the first time I'm 
> > using multichannel PCM.
> > 
> > Front left and right, and rear left and right all work fine. The 
> > centre and sub woofer are swapped though, which doesn't do David 
> > Attenborough's voice any favours. I can confirm this using the
> > speaker 
> > test screen, which also uses multichannel PCM.
> > 
> > I'm using a Raspberry Pi and OpenMax audio. Is there any way to 
> > correct the channel mapping? I suspect I might be able to use the 
> > vcgencmd hdmi_channel_map command, but I've no idea how to
> > generate 
> > the correct value.
> > 
> > Any insights you can provide would be much appreciated.
> > 
> > Thanks,
> > Andrew
> > 
> > 
> 
> Does the HDMI connection go direct to the Onkyo? If you are using a 
> toslink optical or coax connection, they don't support multi-channel
> PCM.
> 
> Make sure you have selected the correct number of speakers in the 
> "Speaker configuration". You can also try switching this between 5.1
> and 
> 7.1. Different selections will change the way the channels are
> mapped.
> 
> Another thing you can try - there are two ways to get digital audio
> from 
> Raspberry pi, using ALSA or OpenMAX audio (see 
> https://www.mythtv.org/wiki/Raspberry_Pi#Digital_Audio_with_ALSA and 
> https://www.mythtv.org/wiki/Raspberry_Pi#Digital_Audio). I believe
> the 
> ALSA method is superior, so I would try that.

I had the swapped center/subwoofer problem many years ago with a
different receiver/amplifier.  IIRC, I fixed it by remapping the
channels in the ALSA configuration.  See the "Zotac ION / NVIDIA ION"
section of https://www.mythtv.org/wiki/Digital_Audio_Tutorial for an
idea of how to do this.

David



More information about the mythtv-users mailing list