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[RayDiant]

This isn't a problem, it is more to understand how JRiver operates.

For the audio for movies I have an ok external receiver (Pioneer VSX something) that is rather old now, so doesn't have HDMI. I connect to it via SPDIF TOSLINK. This receiver is capable of decoding dolby digital (AC3) and DTS 5.1 (it also does Pro-Logic but I rarely see it used). I use the audio capability of my Asrock Z97 Extreme 4 mother board. In Windows 8 this is RealTek High Definition Audio Optical Output.

In JRiver I use WASAPI. I have selected Bitstreaming SPDIF to the receiver. Everything else is pretty standard. If I select anything other than 2 channle output in JRiver DSP I get an error. This makes sense because SPDIF is really only capable of 2 channels.

This setup plays anything I throw at it. I have downloaded a Dolby ATMOS demo and it plays fine. When the source is Dolby Digital or DTS 5.1 (not EX or 7.1 or any uncompressed x.y signal) it shows on the receiver. Anything else (including the ATMOS) my receiver thinks it's getting a stereo signal.

This is what I think is happening:
1. JRiver does some quick analysis of the audio.
2. If it is Dolby Digital or DTS it pumps the bit stream straight to the receiver
3 If it's anything else JRiver does some kind of processing on it to allow compatiibility with the SPDIF specs of the motherboard (how do I know what this is and how can I change it?)

If I turn off the bitstreaming everything still plays but the receiver only displays that it is receiving a stereo signal so I assume the smarts are in JRiver.

Is my assessment of what is happening correct? Is there someplace where there is more detail on how this happens?

[RoderickGI]

You are pretty much correct in your assessment. The key to what is happening is that you are using a S/PDIF optical connection to your receiver.

S/PDIF isn't just "really only capable of 2 channels", it is only capable of Bitstreaming two channels of PCM data. It doesn't have the bandwidth to Bitstream any more channels. Of course it can also transfer compressed AC3 and DTS 5.1, as you have observed, which I guess is Bitstreaming the original source if it is in that format. Hence 3., if MC detects anything other than AC3, DTS 5.1, or stereo PCM, it down mixes that audio to stereo, as that is the only format supported by your audio device when truly Bitstreaming channels, as you have asked it to do.

I have basically the same setup as you. A HTPC sending audio out via a motherboard based S/PDIF optical cable, to an old receiver that only support AC3 and DTS 5.1. As I want to do room correction on all my audio, and up mix it all to 5.1 channels, I don't Bitstream. I allow MC to decode all audio, apply the DSP changes I have defined, then compress the result back to AC3 in 5.1 channel format. This is set in the "Options/Audio/DSP & output format (DSP Studio)/Output Encoding" field, with a value of Dolby Digital (AC3).

In order to see what MC is doing, next time you are playing something hover your mouse over the Audio Path icon in Standard View and MC will show you exactly what the input is, what it is doing to that input, and what the output is.

[Hendrik]

You could also tell MC to encode all other audio to Dolby Digital (ie. AC3), that way you can get 5.1 over SPDIF at a slight audio quality loss (since DD/AC3 is a lossy format).

[RayDiant]

Thanks for the replies and the tip about the audio path - that will help on my quest. I am playing with various options to get the best sound.