Contour Digital Output Options - Which is Best?

Hi HamsterDR,

I apologize for the delayed response. I wasn't able to find the answers with the information available to me at this time.  I've forwarded your question to our Product Team for review. I'll let you know once I get a reply back. 

Thanks for trying to get the information.  While everything seems to be working with the AC-3 setting now, the Onkyo receiver switches to Dolby Digital when it is connected to the Cox Contour box.  The receiver has _lots_ of different audio settings that can be selected - and I think I would prefer to have the receiver do the audio processing and not the Contour box.  Hence my curiosity about this setting.

David

I think I have the answer since I used to work in the home theater biz a while back.

The PCM output is better quality; but only outputs in stereo.  The AC-3 or Dolby Digital setting will send the full surround bitstream to your Onkyo receiver.

So, if you have a 5.1 speaker setup with a center and rear speakers in your room, I would strongly recommend the AC-3 setting.  You will then get the discrete 5.1 channels from whatever channel you are watching.  Use the PCM setting if you are only running left/right stereo speakers and nothing else.

Someone else (on the Onkyo forum) said essentially the same thing.  I actually have a 7.1 system (THX) system, but don't expect to make any use of that for the TV signals.  Most of the better TV audio is Dolby 5.1 (e.g., HBO Game of Thrones), so that is what I use for TV.  I would still like to know if the PCM signal is compressed.  It seems to be designed to be used for direct connection to TVs which are going to be two speaker systems, so a compressed 2-channel PCM signal would make sense there.

David

I have my 8742HDC connected to a Pioneer SC-1522 AVR via HDMI.  Did a test, switched the DVR from AC-3 to PCM and back again while watching the input on Pioneer's Android app.  I didn't see any change, I had DD - 6.1 ch - 48.0kHz in regardless of setting.  I wasn't sure if the setting applies only to S/PDIF or both that and HDMI.  The description on digital audio settings screen says: "Connect your receiver to the SPDIF-enabled receiver port for accurate sound .....".  So I connected an optical cable from the DVR to AVR.  Using the optical S/PDIF connection, I got PCM - 2.0 ch - 48kHz from the PCM setting and DD - 6.1 ch - 48kHz from the AC-3 setting.

This says the digital audio setting doesn't effect HDMI audio but does have an effect if you are using S/PDIF.  HTH.

Thanks very much for the work to test this. So, the bottom line is that if you are using HDMI to connect the setting makes no difference! It would be very nice to have the Cox support folks confirm this - but it makes a lot of sense, and is what I think I have been seeing when I ask the Onkyo to show me the audio input format. Unfortunately, I am still having issues with the Onkyo HDMI through function stopping working. It seems to be related to changes to the Cox Contour box. Earlier this week, the Contour software update froze and Cox support had me power off the Contour and restart it. That fixed the Contour problem, but the Onkyo stopped outputting any audio.  I unpluged the Onkyo and then plugged it in again, and it says "restarting HDMI" - and then everything works again.  I am going to have to pursue this more with them.  They do say to turn off the source, receiver and TV when HDMI changes are made - but I have tried that and it doesn't help.  (Everything has software now.)

Thanks again for the research!

David

I apologize for the delayed response. I got with one of our Video Engineers about your situation. 

It is true that LPCM is superior to PCM. It is also likely that both PCM and LPCM will be superior to AC-3 because of the trade-offs made by Cable companies and Programmers (the source of the TV content). The trade-off is due to the fact that AC-3 is a compression technology that is lossy. This means that you can trade-off quality for bitrate. As you decrease the audio’s bitrate to save on B/W, then the quality of the audio is reduced. So it turns out that the AC-3 audio is what determines the quality of the audio that you hear. The trade-offs have usually been made by the Programmer when sending a TV channel (service) to Cox via satellite or by some other path (like over-the-air). The Programmer has already made bit rate vs quality decisions when encoding the audio via AC-3. At this point you cannot improve the audio’s quality by any amount of AC-3 decoding and by any amount of “processing”. 

So the quality that you hear is locked in by the AC-3 encode/decode process. In your home it does not matter if you decode the AC-3 audio in the STB or in the Receiver. You will experience the same level of audio quality. And it will not matter if you use the HDMI I/F vs the Optical Audio Out I/F. These  two paths both offer a superior method of transmitting the audio from the STB to the Receiver vs the AC-3. When AC-3 is used, you cannot improve the audio quality once it is decoded; so it does not matter whether the decoded audio is transmitted via PCM or LPCM the rest of the way.

StephanieA said:

So the quality that you hear is locked in by the AC-3 encode/decode process. In your home it does not matter if you decode the AC-3 audio in the STB or in the Receiver. You will experience the same level of audio quality. And it will not matter if you use the HDMI I/F vs the Optical Audio Out I/F. These  two paths both offer a superior method of transmitting the audio from the STB to the Receiver vs the AC-3. When AC-3 is used, you cannot improve the audio quality once it is decoded; so it does not matter whether the decoded audio is transmitted via PCM or LPCM the rest of the way.

I'm not sure I understand your point, Stephanie.  Of course, no processing will substantially improve the quality over the original source.  But ... the setting does matter if you are using Optical Audio Out.  If you select the PCM option over S/PDIF the DVR (at least my 8742HDC) only outputs 2.0.  The DD (AC-3) option outputs 5.1 or 6.1.  The setting doesn't seam to matter when using HDMI for audio, both settings output 5.1 or 6.1.

Therefor, the sound quality may be limited by the source encoding, but the Contour settings do matter if you are using the Optical interface.  It does matter how the decoded audio is transmitted if the decoding/transmission process down-converts from multichannel to two channel stereo.

As has been noted, when using HDMI to connect the Contour box to a receiver and then on to the TV, these settings make no difference.  But as Stepanie has noted, the original audio quality that Cox gets does make a difference.  I have noted these differences.  I get Dolby Digital signals from the Contour, but the DD seems to be much higher quality when I view HBO programs.  In fact, I have listened to HBO movies and specials in which the DD (5.1) signal sounds much better than the THX processing I use on the Onkyo for most BlueRay movies coming directly from my Sony BR player.  Most regular TV audio is barely stereo (which is why I leave the receiver off most of the time when watching TV).  Most people probably don't care about audio quality, but a few of us do.  (HBO Go also seems to deliver better audio.)

David

AllenP said:

StephanieA said:

So the quality that you hear is locked in by the AC-3 encode/decode process. In your home it does not matter if you decode the AC-3 audio in the STB or in the Receiver. You will experience the same level of audio quality. And it will not matter if you use the HDMI I/F vs the Optical Audio Out I/F. These  two paths both offer a superior method of transmitting the audio from the STB to the Receiver vs the AC-3. When AC-3 is used, you cannot improve the audio quality once it is decoded; so it does not matter whether the decoded audio is transmitted via PCM or LPCM the rest of the way.

I'm not sure I understand your point, Stephanie.  Of course, no processing will substantially improve the quality over the original source.  But ... the setting does matter if you are using Optical Audio Out.  If you select the PCM option over S/PDIF the DVR (at least my 8742HDC) only outputs 2.0.  The DD (AC-3) option outputs 5.1 or 6.1.  The setting doesn't seam to matter when using HDMI for audio, both settings output 5.1 or 6.1.

Therefor, the sound quality may be limited by the source encoding, but the Contour settings do matter if you are using the Optical interface.  It does matter how the decoded audio is transmitted if the decoding/transmission process down-converts from multichannel to two channel stereo.

There might have been a mis-understanding with my post. I was focusing more on how the audio is delivered and not the specific settings for different connections.

The settings will make a difference because PCM over the S/PDIF, whether it be connected via coax or TOSLINK, is limited to 2 channels when carrying uncompressed audio.  HDMI does not have this limitation.