Question about 5.1 Surround Format

I recently upgraded the speakers in my audio system and decided to hook up the old speakers to my TV through an old Pioneer A/V receiver. I don't have the room for a 5.1 system and just want to listen in two channel stereo. I was recently playing a DVD that only has a 5.1 surround sound track, and it seemed to come out in stereo with the surround feature turned off on the A/V receiver. I was thinking of upgrading the Pioneer A/V receiver to improve the sound, and was wondering if I could use a two channel receiver with no surround decoding capability, yet still have it play two channel stereo regardless of the audio format coming out of the DVD player?

So my question is: What exactly is the format of the two channels coming out of the DVD when it is outputing a surround sound signal? Is it a true stereo signal, and the A/V receiver is decoding high frequency information to create the 5.1 channels? Or is it some other format and the A/V receiver needs to decode it to reconstruct the two channel stereo signal? If it is the first case, would I be OK using a two channel receiver? A link to a website that describes the process of encoding/decoding would also be helpful.
Two channel stereo receivers don't have digital inputs. You will use the dvd players L=R analog outputs...stereo.

With your surround receiver set to no center or rear, those channels are folded into front L=R I beleave. All DVD's have a stereo can choose that as default in the player setup menu also.


I'm using the right and left audio outputs out of the DVD, but I think the audio can come out either in stereo or Dolby Pro Logic (not the 5.1 surround which is digital.) I looked up Dolby Pro Logic in wikipedia:

and it says:

"Dolby Surround/Pro Logic is based on basic Matrix technology. When a Dolby Surround soundtrack is created, four channels of sound are matrix-encoded into an ordinary stereo (two channel) sound track by using phase shift techniques. A Pro Logic decoder/processor "unfolds" the sound into the original 4.0 surround—left and right, center, and a single limited frequency-range mono rear channel—while systems lacking the decoder play back the audio as standard Stereo."

So what I think is happening is that the A/V receiver is decoding the Pro Logic in surround mode and playing it in stereo with the surround off.

I'll look to see if there is an option on my DVD player to always output a stereo signal (versus Dolby Pro Logic), but I don't remember one. I think it just outputs whatever audio format you are choosing on the DVD. The DVD in question has only two English tracks: a 5.1 surround sound and a two channel stereo with the Director's comments. When I choose the 5.1 surround sound, I think the Dolby Pro Logic signal is coming out.

So if the Wikipedia page is correct, a 2-channel receiver without a decoder will play back a Pro Logic signal in standard stereo. Does this make sense and can anybody verify this? I guess I'd like to know how the Matrix encoding is working to convince myself that it is not affecting the fidelity of the 2 channel signal.