Digital Optical only 2 channels?

assoc

macrumors member
Original poster
Jul 14, 2013
46
5
I connected a 5.1 speaker system to my Mac Pro 2010 (OS 10.13.6) via the built in digital optical, but I can't select anything except 2 channels in Audio MIDI Setup. What's the deal?
 

crjackson2134

macrumors 601
Mar 6, 2013
4,571
1,680
Charlotte, NC
That’s correct, digital optical is 2-Ch only AFAIK. You would need a sound processor box (HTS or similar) that could split a compressed signal into 5.1/7.1 outputs.

I’m not an expert on this, so don’t take it to the bank. It’s just from recall, as I found myself in a similar position when I moved to Mac a few years back.
 
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thornslack

macrumors 6502
Nov 16, 2013
410
160
Optical supports 5.1. I don’t know if it can support 7.1 however.

Most media is stereo, so if you’re playing a stereo source expect stereo output.

The real question is what is the media you’re playing and what programs are you using to decode it? Do you have a receiver?

The DVD player supports multi channel output. So can iTunes under certain circumstances. VLC will pass encoded audio via tos link.

If memory serves you should have the ability to select 8 or 6 channel audio in the audio/midi section then configure speakers to 5.1. This will then output PCM surround audio. Even with 2 channel audio selected or PCM I know that VLC will pass multi channel audio (DD/DTS) direct as is.
 
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crjackson2134

macrumors 601
Mar 6, 2013
4,571
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Charlotte, NC
Optical supports 5.1. I don’t know if it can support 7.1 however.

Most media is stereo, so if you’re playing a stereo source expect stereo output.

The real question is what is the media you’re playing and what programs are you using to decode it? Do you have a receiver?

The DVD player supports multi channel output. So can iTunes under certain circumstances. VLC will pass encoded audio via tos link.

If memory serves you should have the ability to select 8 or 6 channel audio in the audio/midi section then configure speakers to 5.1. This will then output PCM surround audio. Even with 2 channel audio selected or PCM I know that VLC will pass multi channel audio (DD/DTS) direct as is.
Good Stuff! I gave up on it a long time ago.
 

bsbeamer

macrumors 68030
Sep 19, 2012
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BELIEVE may be limited to 5.1 with a hardware decoder in place. Recall trying to setup more than that at a client's office several years ago and ran into so many issues they just went with a different solution (via AJA Kona breakout box). I believe optical worked with DVDs back in the day and assume QT/VLC/iTunes would as well.

This thread may be helpful:
https://forums.macrumors.com/threads/configure-5-1-audio-out-on-mac-pro-5-1.2033103/
https://forums.macrumors.com/threads/5-1-audio-on-mac-pro.423024/

There are some really inexpensive USB cards that provide easier mapping without dedicated hardware decoder (receiver-style amplifier) in place if you want to use monitor-style speakers for each channel.
 

handheldgames

macrumors 68000
Apr 4, 2009
1,706
928
Pacific NW, USA
BELIEVE may be limited to 5.1 with a hardware decoder in place. Recall trying to setup more than that at a client's office several years ago and ran into so many issues they just went with a different solution (via AJA Kona breakout box). I believe optical worked with DVDs back in the day and assume QT/VLC/iTunes would as well.

This thread may be helpful:
https://forums.macrumors.com/threads/configure-5-1-audio-out-on-mac-pro-5-1.2033103/
https://forums.macrumors.com/threads/5-1-audio-on-mac-pro.423024/

There are some really inexpensive USB cards that provide easier mapping without dedicated hardware decoder (receiver-style amplifier) in place if you want to use monitor-style speakers for each channel.
Optical connections can easily carry a 6,1 signal. Your media just needs to pass through the bitstream audio to your av receiver with the appropriate decoder, such as Dolby Digital EX. The transition to HDMI that included digital video and audio pretty much made the optical interface obsolete.
 
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sailmac

macrumors 6502
Jan 15, 2008
315
72
I have the Optical Digital output connected to an AV receiver (Yamaha RX-V659). The receiver decodes whatever signal the Mac Pro sends to it. I can confirm it passes 5.1 from VLC.

I haven't tried 7.1 but I too seem to recall this optical connection won't support it.
 

kings79

macrumors regular
Sep 16, 2015
148
93
It depends on the send and receive software/device. And the correct setup.
 

assoc

macrumors member
Original poster
Jul 14, 2013
46
5
Looking in Audio MIDI I cannot select anything but 2 channels. The device on the other end is a 5.1 speaker setup.

Screen Shot 2019-02-19 at 1.03.06 AM.png
 

thornslack

macrumors 6502
Nov 16, 2013
410
160
We really need more information to help you. What is the source material you’re playing? What programming are you using to play the source material? What hardware recieves the outputted audio?
 

MacsRgr8

macrumors 604
Sep 8, 2002
7,832
1,126
The Netherlands
But, does 5.1 work in VLC while selecting digital passthrough?

I also have a 2010 Mac Pro connected to a 5.1 / 7.1 receiver via digital optical and the Audio Midi Setup doesn't show the multichannel options either, but using VLC the receiver shows the Dolby DTS / 5.1 if digital pass though is selected.

So, VLC works, Audio MIDI Setup does not.

I have only seen Audio Midi setup work multichannel via HDMI.
 

thornslack

macrumors 6502
Nov 16, 2013
410
160
TOSLINK can only pass through compressed multichannel audio. So you won’t get the discrete channel options in audio/midi. My earlier post where I mentioned 6 or 8 channel audio from memory was confused with my HDMI set up. But it will still carry 5.1 source to a capable receiver.
 
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assoc

macrumors member
Original poster
Jul 14, 2013
46
5
OK, I think I understand things now. I'll stop worrying about Audio MIDI and dig out a source to test passthrough.
 

flyingmanatee

macrumors member
Jan 7, 2014
67
8
Oregon
As thornslack m For PCM audio, SPDIF only carries 2 channel as its an AES3 standard . All other bit streams are passthroughs, as ultimately its a linear direction data output, long as its under 25 mbps-ish a second. TrueHD is max of 18 mbps, at 5.1. If I remember correctly 7.2 for the lossless formats is about all the more that SPDIF does. Otherwise you need a higher bandwidth connection, like HDMI.

Also, can confirm as early as 2003 that VLC has had the ability to pass through AC3 (Dolby Digital) and other formats. If you're doing multichannel mixing, generally you're either aggregating multiple outputs, using a connection that does discrete multi-channel (it basically is numb to the fact you're mixing for surround sound) or just going analog to a receiver/mixer/whatever.