All I can think of is RCA to HDMI converter ~ these take 3 x RCA in (composite + left/right audio) and output to HDMI. I got one around 5 years ago and it would convert/passthru the audio without need for the composite video signal. Gets it's power from the HDMI connector, and obviously you need a 3.5mm audio jack to 2 x RCA cable. Note: I'm not sure if newer units follow the same design, but do be aware there can be a small delay/lag in the audio path compared to the video path (to display)...I was getting around 10ms lag.

There may be older AV receiver/amplifier units that have an analogue multi-channel input and an HDMI output that can digitize and pass through said analogue input to said HDMI output.

There is also the option of using a multi-channel audio interface and DAW type software to do this on a modern PC.

Yet another, more DIY, option would be to use a dedicated lower power PC or a Raspberry Pi and a few sound cards under Linux to do this . It would be similar to this Not so crazy idea : using a Raspberry Pi 4 with jackd , Zita A2J bridge and jack_mixer to make a software S/PDIF mixer , but instead of mixing, one would just map input channels to the corresponding output channels, so it would be simpler in fact .

you mention HDMI or OPTICAL.

the latter is very cheap and easy to convert.

just type "rca to optical audio converter" into amazon. The ones I see are <$20.

and if it HAS to be HDMI, there is the Monoprice Blackbird https://www.monoprice.com/product?p_id=13347

luckybob wrote on 2023-10-27, 02:08:

you mention HDMI or OPTICAL. […]
Show full quote

you mention HDMI or OPTICAL.

the latter is very cheap and easy to convert.

just type "rca to optical audio converter" into amazon. The ones I see are <$20.

and if it HAS to be HDMI, there is the Monoprice Blackbird https://www.monoprice.com/product?p_id=13347

There is a caveat here.

HDMI can carry multi-channel (including 5.1 ) uncompressed digital audio.

OPTICAL (aka S/PDIF aka IEC958) can only carry uncompressed stereo (2 -channel) uncompressed digital audio. For an such an OPTICAL connection to carry more than 2 channels (including 5.1), the data must be compressed, otherwise there would simply not be enough bandwidth. Typically, the most commonly used codecs for this are Dolby Digital (AC-3) and DTS .

None of the cheap "(analogue) rca to optical audio converter" that I have seen offer more than 2 channel input. Maybe there exist multi-channel input capable ones that compress to Dolby Digital or DTS and output through OPTICAL, but I do not recall ever seeing one like that personally. The equivalent to this could probably be functionally DIY-ed on a Raspberry Pi or Linux PC, but the real-time compression requirements might pose a challenge (expecially in terms off added latency).

The Monoprice https://www.monoprice.com/product?p_id=13347 has no analogue inputs, so it would not help for the OP's use case .

@andrean What 5.1 sound cards with analogue outputs did you have in mind ?
Some of the Creative Labs ones also had an optical output and could be made to work with an optionally purchasable Dolby Digital Live encoder which would would allow realtime compression of 5.1 audio into Dolby Digital and output through the optical out (DTS Connect was a similar option for DTS output). AFAICR, there was also a way to do this with free third party software which may or not have required the use of third party KX Project drivers (sorry, I last tried this about 20 years ago)

darry wrote on 2023-10-27, 05:17:

There is a caveat here. […]
Show full quote

luckybob wrote on 2023-10-27, 02:08:

you mention HDMI or OPTICAL. […]
Show full quote

you mention HDMI or OPTICAL.

the latter is very cheap and easy to convert.

just type "rca to optical audio converter" into amazon. The ones I see are <$20.

and if it HAS to be HDMI, there is the Monoprice Blackbird https://www.monoprice.com/product?p_id=13347

There is a caveat here.

HDMI can carry multi-channel (including 5.1 ) uncompressed digital audio.

OPTICAL (aka S/PDIF aka IEC958) can only carry uncompressed stereo (2 -channel) uncompressed digital audio. For an such an OPTICAL connection to carry more than 2 channels (including 5.1), the data must be compressed, otherwise there would simply not be enough bandwidth. Typically, the most commonly used codecs for this are Dolby Digital (AC-3) and DTS .

None of the cheap "(analogue) rca to optical audio converter" that I have seen offer more than 2 channel input. Maybe there exist multi-channel input capable ones that compress to Dolby Digital or DTS and output through OPTICAL, but I do not recall ever seeing one like that personally. The equivalent to this could probably be functionally DIY-ed on a Raspberry Pi or Linux PC, but the real-time compression requirements might pose a challenge (expecially in terms off added latency).

The Monoprice https://www.monoprice.com/product?p_id=13347 has no analogue inputs, so it would not help for the OP's use case .

@andrean What 5.1 sound cards with analogue outputs did you have in mind ?
Some of the Creative Labs ones also had an optical output and could be made to work with an optionally purchasable Dolby Digital Live encoder which would would allow realtime compression of 5.1 audio into Dolby Digital and output through the optical out (DTS Connect was a similar option for DTS output). AFAICR, there was also a way to do this with free third party software which may or not have required the use of third party KX Project drivers (sorry, I last tried this about 20 years ago)

I got a couple different Creative cards, Audigy 2 ZS, Live! 5.1, ... , attached are picures of the cards, as far as I can tell, none of them have optical output.

Regarding stereo encoding only, I indeed found an RCA2HDMI converter as mentioned in this thread, which will work fine for older cards with stereo only output, but I'd still like to figure out a solution for 5.1 output as well (if possible).

andrean wrote on 2023-10-28, 07:53:

I got a couple different Creative cards, Audigy 2 ZS, Live! 5.1, ... , attached are picures of the cards, as far as I can tell, none of them have optical output.

Creative made an optical addon module.

"Digital I/O Module"
Re: Different versions of Live Drive?

DerBaum wrote on 2023-10-28, 07:58:

Creative made an optical addon module. 39417_4b.jpg "Digital I/O Module" Re: Different versions of Live Drive? […]
Show full quote

andrean wrote on 2023-10-28, 07:53:

I got a couple different Creative cards, Audigy 2 ZS, Live! 5.1, ... , attached are picures of the cards, as far as I can tell, none of them have optical output.

Creative made an optical addon module.
39417_4b.jpg
"Digital I/O Module"
Re: Different versions of Live Drive?

ah interesting, didn't know about that, although, this will also only forward stereo, not compress all the channels right?

andrean wrote on 2023-10-28, 08:57:

DerBaum wrote on 2023-10-28, 07:58:

Creative made an optical addon module. 39417_4b.jpg "Digital I/O Module" Re: Different versions of Live Drive? […]
Show full quote

andrean wrote on 2023-10-28, 07:53:

I got a couple different Creative cards, Audigy 2 ZS, Live! 5.1, ... , attached are picures of the cards, as far as I can tell, none of them have optical output.

Creative made an optical addon module.
39417_4b.jpg
"Digital I/O Module"
Re: Different versions of Live Drive?

ah interesting, didn't know about that, although, this will also only forward stereo, not compress all the channels right?

Indeed, you will still need software to do that. AFAICR, their might have been dome driver sets (modded ones, most likely) that included that functionality.

I have one of those and it works well, but it is quite difficult to find, AFAIK. Getting an I/O bay or LiveDrive! (as appropriate) is likely easier.

EDIT : On at least some of the Live! cards, you can get S/PDIF output like this [1] in a DIY way ( the post talks about DOS, but this works in Windows too). On later cards, one would need to simulate the detection of an I/O bay connected to the header for that to work, AFAICR , and no one yet has succeeded in doing that, AFAIK.

[1]
Re: sblive dos digital output

andrean wrote on 2023-10-28, 08:57:

ah interesting, didn't know about that, although, this will also only forward stereo, not compress all the channels right?

To be fair... i never used them... At the moment they just look nice in the collection between other Creative stuff...

darry wrote on 2023-10-28, 14:08:

...it is quite difficult to find, AFAIK....

yes. in 15 years of collecting i found exactly 2. and one of them i had to import from japan...

The Sound Blaster Live on the 3rd pic and Audigy 2 ZS have digital output on the sound card. Check this thread for pics of the 3.5mm adapter or cable needed, which is on the 3rd post.
Creative Audigy 2 ZS question - Head-Fi

I can't remember if the Audigy2 ZS supports Dolby Digital Live. With DDL, the software will encode any audio to the receiver.

Without DDL, you can only use the digital output to pass 5.1 encoded audio with DVD Player software. You also send any 2-channel audio through the digital output.

For 5.1, maybe just get any cheap sound card that can do optical out, or - even better - any cheap graphics card that has HDMI out with built-in HDA codec.

For analog stereo, I can think of two cheap options:

There are VGA to HDMI adapters that have a 3.5mm input and are powered by 5V power from a single USB A port. The audio will be injected into the HDMI signal. Cheap (a few Euros on Amazon), so worth a try if you want to check if you are happy with the quality.

Alternatively, the OSSC can take VGA + 3.5mm audio and also convert it to HDMI, with better quality.

darry wrote on 2023-10-28, 14:08:

...it is quite difficult to find, AFAIK....

yes. in 15 years of collecting i found exactly 2. and one of them i had to import from japan...
[/quote]

I got mine locally, brand new, at a store that no longer exists. That store had another, new in box,that was on display for years. They were not popular at the time, I imagine. May taking one apart to see if it can be reproduced easily would be a worthwile pursuit. AFAICR, from my summary tests years ago, this thing is not just connected straight through.

darry wrote on 2023-10-28, 22:05:

...May taking one apart to see if it can be reproduced easily would be a worthwile pursuit...

here you can have a look inside both versions : Re: Different versions of Live Drive?

DerBaum wrote on 2023-10-28, 22:39:

darry wrote on 2023-10-28, 22:05:

...May taking one apart to see if it can be reproduced easily would be a worthwile pursuit...

here you can have a look inside both versions : Re: Different versions of Live Drive?

Thank you! I apparently missed that thread.

Interesting, though none of the solutions are really of the plug'n'play type, even though it sounds like it should be. Maybe there is a niche market for such a device, 5.1 to HDMI audio encoder, it could be the OSSC / Retrotink / Morph equivalent for sound, product idea for indie hardware hackers 😀

There was a niche market for something like this 15 years ago, it doesnt exist anymore. Everything generates sound natively thru hdmi/DP/usb.