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Dolby Digital Question

post #1 of 3
12/15/08 at 5:22am
Thread Starter 
I am new to this forum so I'm not sure if this question is posted in the right thread, but here goes.

I am not that smart with home audio and tv equipment and I have recently been working on getting better with understanding how it all works. Last year I bought an Onkyo SR875 receiver and then an LCD 42' toshiba flat screen HDTV. I have 5.1 surround system with all klipsch speakers.

My question is about my audio signal. I have everything (DVD player, DVR) connected to my receiver via HDMI and then running to my TV via HDMI. I remember when I first hooked up my system that my audio signal from my DVD was dolby digital. Now I cannot get the dolby digital signal from my DVD. Last night I was watching football and was able to pickup the DD signal, but about 30 minutes later it cut out. I tried playing a movie (LOTR) and could not get dolby digital. I tried changing out the HDMI ports that the cables were plugged into thinking it might be a loose connection, but that didn't help.

After reading my receiver manual I displayed the audio output from my DVD player and it reads PCM. I tried to set the Audio Selection to "AUTO", but the receiver would only let me set HDMI or ANALOG.

Tonight I am going to try and reset my receiver and start over, but am I doing something wrong to get the DD signal?
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post #2 of 3
12/15/08 at 6:56am

Re: Dolby Digital Question

PCM is still digital, but it's the digital format used on regular 2.0 channel CDs. You can also get 5.1/7.1 PCM (MPCM) from HD-DVD/Blu-ray. There may be some SD-DVD players that decode DD/DTS internally to MPCM, but I'm not sure.

What exactly is displayed on the 875 front panel when you're checking this? The 875, like my 805, should have small icons that light up to indicate DD, DTS, PCM, etc. Which of the little speaker lights were on...this indicates the number of input channels the 875 is receiving? The main LED text will indicate your selected source and the listening mode (DPL IIx, THX Cinema, Pure, etc.) being applied.

You need to make sure your DVD is set to bitstream audio and you select the desired soundtrack on the disc...most titles will default to DD on SD-DVD. Likewise, your DVR needs to be set for Dolby Digital (DD). Both types of devices will usually allow you to select a downmix to PCM option, whether intentionally or not. ;-)

Make sure you've got "HDMI Audio Out = Off" in the 875. HDMI Audio Out tells the 875 to pass the audio signal on to the display without processing it. If it's ON, the 875 will be forced to downmix to 2.0 channel PCM as it's likely your TV cannot handle a 5.1 channel mix. I believe, although I've never checked, that the input speakers should still light up to indicated 5.1 received when this happens...althought it's possible the 2.0 PCM instruction from the TV might flow all the way back through to the source.

It's helpful when coming to forums for troubleshooting if you include the model numbers of all equipment invovled. Some of us are willing to download owner's manual as part of trying to help.

Lastly, at least with my cable provider, sometimes the DD signal will drop down to PCM during a broadcast. Same happens with the HD feed of a signal dropping to SD...there's really no way to tell if the fault lies at the broadcast source or your local cable head. Also, a number of my local network affiliates are only sending out 2.0 DD at the moment...DD itself is no guarantee of 5.1, it can be up to 5.1, but could be 1.0.

-Brent
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post #3 of 3
12/15/08 at 9:53am
Thread Starter 

Re: Dolby Digital Question

Thanks brent I will try these out tonight.

I remember checking the dvd audio source and it was set 5.1 DD. So I can eliminate that.

When I was watching TV the front display read Dolby digital. When the "cut out" the display only ready stereo. I tried changing the listening mode but DD wouldn't come back. When I selected "Display" on the receiver it shows DD 2.0. So given that cable can very in it's audio source then only way to really test is with the DVD.
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