Would you (could you?) do 5.1 or 7.1 surround from L-R RCAs?

[jbs]

I hope you'll forgive my first post being one that I consider a dumb question, but I want to make sure I'm being fair and not assuming too much. I recently had some home automation and AV work done in our house, including setup of a 7.1 surround media room. Overall I'm very happy with the work, but the audio in the theatre sounded flat. When I started tracing the wires around the equipment rack, I found that the only audio connections from the DVD player and the HD cable box to the receiver were L-R RCA cables. All the equipment has optical audio inputs and outputs, but they were not being used.

The installer, who I like a lot, was chagrined when I pointed it out, apologized and is ready to fix it, but now I'm in a conversation with the guy who sold the system about whether or not L-R RCAs are a reasonable way of delivering sound to a 7.1 speaker setup. He refers to this as "digitally processed audio from a receiver (also “surround sound”)".

Essentially, does the fact that I did not specifically name "digital audio" as the interconnection mean that their solution was appropriate and my request to change to optical is an "upgrade" or would any A/V professional who specified 7.1 surround speakers and a high quality 7.1 capable receiver assume that the audio source, where available, would be optical.

Obviously I would have thought the latter, but if it's really open for interpretation then I don't want to treat him unfairly. In any case, the audio sounds MUCH better since I plugged it in optically, and I'm sure that is the preferred way of doing it, since digitally processed audio from a receiver just means taking the 5.1 channels from the DVD source, compressing them down to L-R, transferring it to the receiver, and then interpolating it back out to cover all the speakers.

Any advice or insight would be much appreciated, and thanks for a terrific forum!!

--Jason

 

[MDS]

In any case, the audio sounds MUCH better since I plugged it in optically, and I'm sure that is the preferred way of doing it, since digitally processed audio from a receiver just means taking the 5.1 channels from the DVD source, compressing them down to L-R, transferring it to the receiver, and then interpolating it back out to cover all the speakers.

That is essentially correct. If a dvd player is connected using analog outputs the dvd player will decode the DD/DTS 5.1, downmix it to 2 channel PCM, and then convert the PCM to analog. To get 'surround sound' from that you have to use a matrix decoder on the receiver (like ProLogic II) to convert the 2 channel analog signal back to 5.1 channels. PLII does a very good job of it and it will sound like surround but it is not quite what was originally recorded on the disc.

Using a digital connection, either optical or coaxial, and configuring the dvd player to output 'bitstream' will send the receiver the bits untouched and the receiver will do the decoding and send each channel to the appropriate speaker.

It kind of goes without saying that a true surround setup requires digital connections and you should expect the proper setup from an AV installer. Don't be harsh when pointing it out to the installer, but definitely have them do it right if you are paying for it.

 

[TLS Guy]

That installer was way out of line. You are correct. Make him do it properly, and tell him not to do that again.