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In Reply to: RE: Question on Dolby Digital Signal Driving "Logic" posted by JoeLip on November 03, 2007 at 11:48:21
I'm in Australia and I don't know what your off air HD broadcasting is like, or the quirks of your Onkyo receiver. There are certainly some quirks with my Denon receiver.
There's a difference between Dolby decoding and Dolby PLII. The first simply decodes the channels in the signal while the second processes the info in the channels that are there to generate info for channels not included in the original signal. It sounds to me as if your off air channels are broadcasting in stereo and your receiver is simply decoding the digital stereo signal to give you stereo. When you swap to analog inputs, you're taking a stereo signal and specifically telling the receiver to use Pro Logic processing to generate the extra channels. It sounds as if both processes are actually working properly.
What you obviously want is some way to tell the receiver to take the digital Dolby signal from the broadcast and to process it with Pro Logic as well as simply decoding it. There should be options for you to be able to do that but it will mean reading the manual. Hint: if you have the receiver set to apply Pro Logic processing to the Dolby bitstream from DVDs which only have a Dolby 2 channel soundtrack, you want to set it to do exactly the same thing for your off air broadcasts.
David Aiken
Follow Ups:
Hi,
Thanks for the response. You're post made me realize what the problem is - it's my SONY TV!! The off-air signal is routed directly to the TV from my attic antenna, and even though I'm going optical to the Onkyo A/V receiver the TV only passes 2-channel stereo, but it must be Dolby Digital stereo. Presently I am using an analog connection as well and that is what I use with the Pro Logic II to generate the 5.1 output. Works really well, and I am just going to stick with that. Geez, you would think that SONY would recognize the need to at least pass through a 5.1 digital signal but they don't. The manual sez 2-channel only.
BTW, the Onkyo doesn't have any quirks, AFAIK. I bought a DENON A/V for my son, and while it performs nicely (it's a cheaper model, 75wpc I think) it is VERY difficult to set-up and use. Really confusing. Oh well.
Thanks again, Joe
Are you sure the problem is the Sony TV? Here in Australia most hi-def off air broadcasts are only stereo anyway. I've yet to come across a 5.1 broadcast signal and I don't know how my set-top box would handle that. One day I may find out but all my local off air broadcasts seem to be stereo only.
If the TV is passing the signal in bitstream, I would have thought it would simply be passing the signal it receives, not converting it to stereo. If it's converting a surround signal to stereo and passing a stereo bitstream, then it's decoding the original bitstream, downmixing to stereo, then re-encoding into a Dolby bitstream and I don't think any TVs do that. If the TV is passing the signal in PCM, then it could be downmixing but then the receiver should show the signal as PCM, not Dolby, since the Dolby decoding has already been done and it's no longer in that format.
If the TV gives you the option of bitstream or PCM digital out, choose bitstream and let the Onkyo do the decoding. That's your best bet of preserving surround channels if the broadcast has a multichannel surround soundtrack. If the broadcast is stereo, that's all you're going to get whether you ooutput in bitstream or PCM digital format, or in analog either for that matter.
David Aiken
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