Multichannel over HDMI

[Tim Curtis]

Hi,

I was testing some 5.1 multichannel audio the other day and noticed that the channel mapping created by ALSA does not seem  to be correct. The sources are 6 channel (5.1) but my AVR indicates it's receiving 8 channels and there is no sound from the rear L/R surrounds.

Sources:
1. Soma FM - Groove Salad Test Streams
https://hls.somafm.com/
HLS format containing 6 channels (5.1) encoded at 320K AAC
https://hls.somafm.com/hls/gs-surround/program.m3u8

2. Test track from @Nutul
FLAC format containing 6 channels (5.1)

Screen shots

       

ALSA speaker-test output 

## 6 channels
pi@sig:~ $ sudo speaker-test -c 6 -t wav -l 1
speaker-test 1.2.4
Playback device is default
Stream parameters are 48000Hz, S16_LE, 6 channels
WAV file(s)
Rate set to 48000Hz (requested 48000Hz)
Buffer size range from 480 to 10922
Period size range from 480 to 10920
Using max buffer size 10920
Periods = 4
was set period_size = 2184
was set buffer_size = 10920
0 - Front Left        OK
4 - Center            OK
1 - Front Right       OK
3 - Rear Right        No sound
2 - Rear Left         No sound
5 - LFE

## 8 channels
pi@sig:~ $ sudo speaker-test -c 8 -t wav -l 1
speaker-test 1.2.4
Playback device is default
Stream parameters are 48000Hz, S16_LE, 8 channels
WAV file(s)
Rate set to 48000Hz (requested 48000Hz)
Buffer size range from 480 to 8192
Period size range from 480 to 8192
Using max buffer size 8192
Periods = 4
was set period_size = 2048
was set buffer_size = 8192
0 - Front Left        OK
4 - Center            OK
1 - Front Right       OK
7 - Side Right        OK - actual output is Rear Right 
3 - Rear Right        No sound
2 - Rear Left         No sound
6 - Side Left         OK - actual output is Rear Left 
5 - LFE

Maybe the HDMI implementation in new RaspiOS Bookworm fixes this but it would be interesting to see if there is some sort of config on Bullseye that would work.

[Tim Curtis]

@Nutul, may I provide your 6 channel FLAC file via PM if someone wants to use it for testing?

It would be useful to have a set of multichannel test files in various formats so feel free to PM me with download links :-)

[Nutul]

@Nutul, may I provide your 6 channel FLAC file via PM if someone wants to use it for testing?

It would be useful to have a set of multichannel test files in various formats so feel free to PM me with download links :-)

I have nothing in contrary, if that's for the benefit of the community, go ahead. :-)

[jcucurull]

I also have problems reproducing multichannel audio. I have an album at 5.1 channels 24/96Khz (decreased to 16 bits due to the HDMI issue), that I can only reproduce in stereo in my AVR. In my case, the AVR shows that is receiving multichannel audio (there is a graphic with the channels received), but on the screen appears STEREO and I cannot change it to mutichannel. It seems some sort of glitch of the AVR because when I try to change to multichannel appears 96Khz blinking, as if it was impossible to change due to some limitation. However, I can reproduce material at 5.1 24/96 using an Oppo Bluray player without issues.

I can test the multichannel if you sent me this test file you were mentioning.

PS: If you say that it is sending 8 channels, maybe the problem with my AVR is that it does not support to receive 8 channels at 24/96 (due to too much data rate), because it is a bit old (Marantz SR-5001) and I know it has limitations. If 6 channels were sent, I guess it should work because as I have mentioned before I use these values from other sources such as the Blueray player.

[Tim Curtis]

Sure, I'll PM you the download link.

[popej]

Are the speaker names correct?

I'm used to "surround" in 5.1 and "surround back" in 7.1. With names form above, I would expect, that going form 5.1 to 7.1 adds "rear" speakers, not "side" speakers.

[Tim Curtis]

Are the speaker names correct?

I'm used to "surround" in 5.1 and "surround back" in 7.1. With names form above, I would expect, that going form 5.1 to 7.1 adds "rear" speakers, not "side" speakers.

It looks like the ALSA speaker-test utility uses names which are not standard. The standard names I'm familiar with are below:

5.1 
FL  Front left 
CNT Center
FR  Front right
SL  Surround left
SR  Surround right

7.1
FL  Front left 
CNT Center
FR  Front right
SL  Surround left
SR  Surround right
SBL Surround back left
SBR Surround back right

[popej]

There is some advice about channel mapping here: https://forums.raspberrypi.com/viewtopic.php?t=307369