PCM Multichannel settings - I'm confused...

[steveharman]

Hi,

This is more of a general query than specific to any particular build, although I'm running the latest 3.2 from feeds.

I've just eBay'd us an all-singing AV AMP (Sony) and hooked it up to the Gigablue Quad via HDMI. Here's what I've found when experimenting with the OpenVix audio settings.

// PCM Multichannel set to YES.

Amp displays: LFE + HDMI + LPC. The GigaBlue controller adjusts the volume up/down successfully but sound from the rear speakers is not great and very quiet.

// PCM Multichannel set to NO.

Amp displays: HDMI + a Dolby symbol & PLII = The GigaBlue controller doesn't adjust the volume but the rear speakers sound really good.

Basically what I don't understand is why with PCM Multichannel enabled the GigaBlue controller adjusts the sound levels OK but sound from the rear speakers is quiet, yet with PC Multichannel disabled the sound from the rear surround speakers is great but the GigaBlue controller doesn't adjust volume levels.

Any pointers would be most welcome!

Thanks,

Steve

[DaMacFunkin]

Because the program or channel you are watching is only in stereo, pcm multi channel will only send audio to the speakers it has information for, although some amps may create a LFE channel depending on how you have your speakers configured. Dolby Pro Logic II will take that stereo feed, analyse it and create a surround field output to all available speakers, sometimes this can be very accurate and sound as convincing as Dolby 5.1, depending on the source of course.

[Joe_90]

If you are using a fully capable AV amp, then you should have your Quad set to PCM Multichannel=NO. Then the Quad will pass the signal to the amp over HDMI to decode. Your amp, if it's a newish model should be capable of decoding DD 5.1, DTS and various others, possibly including DTS-MA etc. On stereo signals from most TV programmes your amp can generate pseudo surround if you use the settings like Neural THX 5.1 or Dolby Pro-Logic or other DSP modes.
Your amp probably will not decode AAC 5.1 over HDMI and that is probably the only instance where the Quad might be of use in decoding to multichannel PCM or transcoding to DD to send to the amp.
When I first saw multichannel PCM setting available in the ViX builds I thought it was there to handle genuine multichannel PCM audio files and send them over HDMI, but I was disappointed to see that it was only there to decode compressed multichannel to PCM. It doesn't actually do a great job either, as you have found.

[peterbr]

Im not sure the answers cover the original post. I observe the same issue
I have AC3 downmix and AAC downmix set to pass through.
Im using a VU Duo4K SE connected via HDMI to a Denon AV receiver
When selecting a TC channel with dolby sound stream I see the following when
When setting PCM Multichannel to NO, AV receiver gets a dolby audio stream
When setting PCM Multichannel to Yes , AV receiver gets a PCM multi channel stream

I did not have this issue when running OPENPlI 8.1 on a VU+ DUO 2 , Dolby audio would always be send through and PCM would always be send through as PCM Multi Channel.
So should the AC3 passthrough not overrule the PCM Multichannel in case of receiving a Dolby audio stream from a tv channel ?

[Joe_90]

This is a pretty old thread that you have resurrected! However, as you are using an AV receiver, I would not use the PCM multichannel options and instead pass through the Dolby audio stream and let the expensive decoders in the amp do the work. Any multichannel stream from satellite is AC3 generally, although some of the radio channels on 19.2E are using AAC. The terrestrial service Freeview uses AAC for multichannel, so in that case you would convert in the VU to multichannel PCM as most AV receivers won't decode AAC.