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For reasons°, I have my PC plugged into my TV via HDMI, which is connected to my AV receiver via optical cable. Since my TV is only detected as 2 channel device, and stuff like games usually don't encode audio (always raw PCM), I can't get surround sound on my AVR.

So if I could encode the 5.1 PCM audio on my PC in realtime before it is sent over HDMI, I could set my TV to pass-through and get surround sound on my AVR.

AFAIK the AC3 patent has run out some time ago, so the encoder should be free to use by now. But I can't seem to find a (free) software, that would let me do as I described. Anyone know how to make this happen? The software that comes with my onboard sound driver doesn't do encoding, I've checked.

° My AVR doesn't support 4k/HDR video.

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  • Ages ago, I had just such a tool on my laptop with optical out, which had to encode all outgoing audio in AC3 so my non-DTS receiver could play surround sound. It's called AC3Filter, but that looks quite defunct now. The code.google.com archive still has some binaries, but I'm not sure whether it works in Windows 10.
    – CodeCaster
    Feb 8, 2021 at 15:43
  • @CodeCaster I think that does the opposite - decode AC3 into multi-channel PCM. I need 5.1 PCM encoded into 2 channel AC3.
    – DanMan
    Feb 8, 2021 at 17:08
  • I think the entire topic of hardware on-the-fly conversions inside computers in general has been avoided by everyone, to avoid breaking proprietary codec rules. As a sound engineer, I can make (& hear correctly whilst I'm making) brand new 5.1 recordings & export in any format I like, but I cannot process them afterwards in the very same computer. Best I can get is a stereo pseudo-process.
    – Tetsujin
    Feb 8, 2021 at 17:13

2 Answers 2

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From memory, can't verify whether it still works nowadays: AC3 Filter is a tool you can install, which uses DirectShow filters to transcode audio.

It is supported by various media player applications. From the docs:

6.2.1 Output

[...]

AC3 encode - AC3 encoding mode. In this mode filter performs decoding of the input stream and post-processing (all filter options are active including changing of speakers number). Then the resulted signal is encoded into AC3 and transfer into external hardware decoder in digital format. This mode is required to transfer multi-channel audio in formats, which are not supported by external decoder

Again, YMMV. Haven't used it in a decade.

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I see three viable options to send 5.1 to your receiver:

  1. Use APO Driver, apply Dolby encoder to your digital HDMI out via that. This solution is less supported, but is the most straightforward that can resolve your situation. Also some games might not properly detect the 5.1 layout, and still send stereo for encoding.
  2. Use a Dolby live encoder capable sound card, connect your AVR via that. Creative still provide those. This solution is more supported.
  3. Use a 5.1 capable sound card, use analog out, send to receiver. This solution can be cheap to implement, if your receiver has analog in. Also most games will properly detect the 5.1 layout.

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