SPDIF can only carry multichannel in compressed formats like some Dolby and DTS flavors, there needs to be support for such encoding in the OS/driver etc. to get multichannel over SPDIF and one will have to live with the additional latency from both encode and then decode processes in the receiving device. Analog multichannel is able to provide uncompressed output and no extra latency which perhaps makes it preferred at least as far as games are concerned.

Tiido wrote on 2023-04-11, 13:05:

SPDIF can only carry multichannel in compressed formats like some Dolby and DTS flavors, there needs to be support for such encoding in the OS/driver etc. to get multichannel over SPDIF and one will have to live with the additional latency from both encode and then decode processes in the receiving device. Analog multichannel is able to provide uncompressed output and no extra latency which perhaps makes it preferred at least as far as games are concerned.

Interesting. Given that the DTT 3500 dates back to 2000, the options for OS' back then would be 98SE and 2000, neither of which I presume have support for the Dolby encodings.
Therefore, I'm interested how the decoder outputs 5.1 channel for anything of that period that's connected to it, given that the only available inputs are front and rear 3.5mm jacks (4.1 maximum), mini-DIN (max 2.1?) and SPDIF.
It has a built-in Dolby Pro Logic encoder, but that's only producing a compressed mono channel for the rear as well as 2-channel stereo (sort of 3.1?).

It probably is for the software DVD players etc. that can send their compressed stream directly over SDPIF to approrpiate receiver device.

I have the 1999 version of the system. 5.1 works and each speaker plays independently when connecting Digital DIN and coaxial SPDIF to the Sound Blaster Live! under Windows 98.

janskjaer wrote on 2023-04-11, 12:39:

My Cambridge Soundworks DTT 3500 decoder has mini-DIN, SPDIF and 3.5mm Front and Rear (no center) input connections.

janskjaer wrote on 2023-04-11, 14:30:

Therefore, I'm interested how the decoder outputs 5.1 channel for anything of that period that's connected to it, given that the only available inputs are front and rear 3.5mm jacks (4.1 maximum), mini-DIN (max 2.1?) and SPDIF.

mini-DIN, or rather Creative's Digital-DIN supports up to 4x S/PDIF outputs (corresponds to EMU10K chip), which gives 8 uncompressed PCM channels.

The front stereo channel is on SPDIFO#0, the rear channel is on SPDIFO#3, the central and subwoofer channels are on SPDIFO#1. The SPDIFO#2 output is a mix of the front and rear stereo channels. These signals can be taken from the AUD_EXT connector (second generation cards) or SPDIF_EXT (first generation cards).

janskjaer wrote on 2023-04-11, 12:39:

Using DIN to DIN connection only produces sound on front- left and right channels when choosing a 4.1 speaker setup.
If I check the 'Digital Output Only' option in the Creative speaker application, only 2.1 channel setup is available.

CT4760 AUD_EXT 40-pin header also has multiple S/PDIF outputs, but it seems to be limited by driver.

janskjaer wrote on 2023-04-11, 12:39:

On a 5.1 channel Live! (e.g. SB0060, SB0100), would this be any different? Is is possible to have 5.1 channel support on using only either the mini-DIN or SPDIF cable?

Digital-DIN connection (multi-S/PDIF output) should work out of the box on a native SB Live! 5.1/CT4660.

janskjaer wrote on 2023-04-11, 12:39:

Does the Sound Blaster Live! support multi-channel over the SPDIF or mini-DIN connections?

Yes, according to old sites, this is quite possible on SB Live! (non 5.1) sound cards.
You can swap CT4760 EEPROM firmware to a SB Live! 5.1 version to unlock all features, but own risk!
https://web.archive.org/web/20010802163203/ht … to-live51.shtml (use Google Translate)
This mod also makes it possible to get analog center/LFE outputs from SPDIFO#1 pin through external S/PDIF DAC.