[Classof83]

I have a HD-PVR attached to the computer. I am currently connected via stereo RCA cables, as the SPDIF optical input of the unit is giving me problems.

I recorded a clip, and I do hear things coming out of the surround sound speakers on my computer. When I go to edit the video in a video editing program, I do see the sound levels on all 5 surround sound speakers, but I can't edit them individually, as I don't think the channels are split up the way they should be, which makes sense, because I am using RCA stereo cables.

But my question is, how come I'm hearing stuff coming out of the surround sound speakers in RCA stereo capture mode?

 

[ScaryBob]

The sound is encoded in Dolby Pro Logic. That provides a certain amount of surround sound. With Pro Logic, there are basically 4 encoded channels, left, right, center and rear. The rear channel is not full range but will provide some surround effect. Decent DACs will take DD5.1, DD Pro Logic II or DD Pro Logic and convert it to analog Pro Logic over stereo. The A/V receiver will then decode the analog Pro Logic. It's not the best sounding scheme but beats losing all surround content.

 

[Classof83]

Ok, I figured something along those lines - that it was simulating the surround sound.

Hopefully I can get the optical connection working - I think it's a software issue. That way I can edit the individual channels, and remove the centre channel when I want, as right now, like I mentioned, it is altogether.

 

[57]

I was optimizing a system for someone the other day who didn't have enough digital inputs on his AVR and he had analogue audio for a rarely used DVD player, so he didn't care... I found it interesting that I put in a test DVD and the AVR was able to decode the LR and RR channels separately using DPLII. In previous testing DPL had provided the 4 channels as mentioned in post 2, but not the 5 as with DPLII. Of course the LFE channel is not there, but I was amazed at how well DPLII decoded the 5 channels via an analogue audio connection (red/white).

 

[ScaryBob]

I noticed this years ago when I had only an analog VCR to record HD (before Bell had an HD PVR.) BTW, DPLII requires three channels for encoding. What you are hearing on stereo cables is DPL, not DPLII.

 

[57]

What you are hearing on stereo cables is DPL, not DPLII

That's what I thought too, but as I mentioned in my previous post, when I put in a test DVD (say AVIA) which sends out the DD5.1 channels, when that signal was sent to an AVR via analogue audio cables, DPLII was able to send discrete signals to the LR and RR channels. Regular DPL would have sent the LR and RR signals to both surround speakers twice, but DPLII did not - it sent the discrete signals, despite using analogue audio cables.

The AVIA DD5.1 signal for example says "Right Rear" and the sound came from the Right Rear (surround) speaker. When he says "Left Rear" it came from the Left Surround speaker. The only signal missing was LFE.

I've run this same test in the past on analogue audio using only DPL and there the two surrounds have always been active at the same time when he says LR and then RR. This recent test was the first time that I've heard discrete channels. I don't come across this often as most people use digital connections, but I always run the test, even with analogue audio cables to ensure that all of the signals are present on the person's speakers. Even if they only run 2 speakers, you can hear the LF (discrete), RF (discrete), C (RF&LF at the same time), LR (RF&LF at the same time), RR (RF&LF at the same time). This test ensures that none of the audio on the original recording is "lost" and is a better test than running the test tones on the AVR itself.

 

[Classof83]

So in my sound editing software (Sony Vegas Pro 10), I can separate the front, rear, centre, and LFE tracks. There is no LFE recorded with the stereo connection.

When I mute the front and rear tracks, and only play the centre, I can hear what is supposed to be the centre channel through my front left speaker, and I hear the background audio (not just the announcer speaking in the NFL clip I play). The front track plays through all speakers, and so does the rear track. Interesting. I wonder why the centre track just plays through the left speaker.

 

[ScaryBob]

DPLII was able to send discrete signals to the LR and RR channels.

Interesting. They must be doing something with phase shifting for those channels. DPL uses 90° out of phase signals for the rear. I'm guessing but they are probably using a different phasing to get discrete rear channels. +60° and -60° makes some sense.