PCM or Bitstream via HMDI To TV? - Canadian TV, Computing and Home Theatre Forums
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post #1 of 8 (permalink) Old 2010-06-22, 03:36 AM Thread Starter
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PCM or Bitstream via HMDI To TV?

This question has been puzzling me for a while, I know that if you set your player to bitstream it is meant for raw digital audio to an A/V receiver via coax or optical, but what happens when it is straight from your player's HDMI output to your HDTV's HDMI input, will the player's bitstream audio output have any effect on the HDTV's internal audio or is there even an audio processor in the HDTV ?

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post #2 of 8 (permalink) Old 2010-06-22, 09:55 AM
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I would suspect this totally depends on your TV and what audio it had the capability to reproduce.
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post #3 of 8 (permalink) Old 2010-06-22, 10:33 AM
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There are probably several things that could happen depending on the makes/models of BD player and TV.

- The TV accepts lossless audio, downconverting it to stereo for its two speakers.
- The TV and BD player "communicate" via HDMI and the BD player sends the appropriate signal to the TV - be it lossless, DDx.y, PCM, etc. (This may even happen in the background and be independent of any settings that you make in the BD player's user audio menu selection)
- The TV doesn't accept certain signals and the BD player needs to be set to PCM for example.
- And so on.

Just as an FYI, this brings up the other subject that many HDTVs will not "passthrough" a DD5.1 signal to its (optical) output for use by an AVR, while some TVs will. See the bolding in the following FAQ:

FAQ - What's Available in DD5.1

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post #4 of 8 (permalink) Old 2010-06-22, 09:29 PM
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I read this thread and the trhead linked from it.

I tried this out. My newish ( 2009 model) Toshiba TV outputs to the digital out when it has a digital audio input from HDMI and interestingly when it only has analog audio while connected via Component.
So for this exercise I disconnected all the Component cables and just had an HDMI cable connected. The tv has a switch in its audio settings to select PCM or Dolby Digital output. I got audio output fine but my AVR did not turn on the Blue "Dolby" light and the display said PCM 48 regardless of the state of the settings of the TV. When I connect the AVR to the (Rogers) stb via coax, I get the light and the display says Dolby 2/0 or Dolby 3/2 depending on the program on the TV.

So three possibilities.
1) My AVR is vintage 2002 and my not like the signal from the TV... but it works fine with optical from my ( also 2002) DVD player. Is there a handshake on Dolby over an optical connection?
2) My TV setting switch doesn't work OR contrary to the manual one has to power cycle the TV when that setting is changed.
3 The Rogers STB doesn't send 5.1 to the TV. I did change the STB settings for digital audio out and tried the possibilities. No difference.

One thing I did not do and one of the FAQs suggests it may have to be done and that is to go through the STB setup with HDMI connected ( I normally use Component and last did the setup with Component connected.
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post #5 of 8 (permalink) Old 2011-03-12, 09:10 PM
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Eperiment with audio

Since all the forums I have read regarding this topic have not been able to truly answer the question i did the following experiment.

First my equipment:

1. 40" LCD-LED Sharp Aquous 700UN, labeled Dolby Digital, and digital output.
2. Bluyray Sharp HPU16
3 DVD/Home theater combo (1080p Upscale) dolby digital II.

Note: No matter what surround signal the receiver gets it always turns on the surround light and displays "Prologic II Movie

The experiment:

Since there is a lot of uncertainty whether the TV can pass the 5.1 (bitstream) signal to the receiver I decide to do the following:

1. Plugged the BR to directly to the Reviver through digital output, and play the BD with dolby 5.1

Result: Great sound effect.

2. Unplugged the the digital cable and passed the sound through the RCA cables using the aux in the receiver. Obviously 2.0 Channels.

Result: Still able to get surround effect, but it sounds to low, so some effects can barely being heard. However, i was able to tell the difference because I just had listened the same scene on digital output.

3. Knowing the difference, I passed the BR audio signal along with video through HDMI to the TV, and then from the TV to the receiver.

Result: If there is difference between test 1 and 3 I cannot distinguish it, so either my ears and brain don care, or the sound is 95-100% the same.

4. I changed from BR to TV (which I know for sure decodes dolby digital), and watched HBO that transmits with 5.1, sending the sound through the digital cable.

Result: I could not tell the difference, it sound same as test 3

5. I unplugged the digital cable from the TV, and sent the audio through RC cables using aux in the receiver.

Result: Same as test 2, Still able to get sorround effect, but it sounds to low, so some effects can barely being heard.

So, after all the testing I left my system plugged the following way:

From BR to TV using HDMI, then from TV to receiver using digital cable.

does the TV can handle 5.1?? I don't really know. All I know is I cannot tell the difference between sending 5.1 direct form BR to receiver, and sending signal first to TV using HDMI and then to the receiver using digital cable.

So leaving my system that way, i can watch the TV with 5.1 signal and watch my BR movies without plugging the digital cable from one device to the other.

I'm not saying that all the other arguments are not correct, I just did the experiments, and here I give you the results. You be the judges of what is going on, and if anybody know why I can tell the difference (if there is any) let me know, it would be nice to know. (arodas@gmail.com)

By the way excuse my English, it is not my first language.

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post #6 of 8 (permalink) Old 2011-03-13, 12:14 AM
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Here's the FAQ on the topic per post 3 of this thread. Read the bolded part.

FAQ - What's Available in DD5.1

Some TVs can pass DD5.1 and some cannot as mentioned in the FAQ. If the HTiB (Home Theatre in a Box) states DPLII (Dolby Pro Logic) instead of something like Dolby Digital, then, even though you may not hear a difference, you're not getting DD5.1 to the HTiB.

If your HTiB says Pro Logic, then it's receiving a two channel signal and not a DD5.1 signal. There is probably something incorrect in the settings of the sending device if you're using a digital cable. Although Pro Logic provides surround sound, it is not totally equivalent to DD5.1. The difference you heard in point 2 may simply have been the analogue audio cables - digital audio cables are superior, but you are still only getting two channels to the HTiB if it's invoking DPL instead of stating something like "Dolby Digital".

See the following post, useful for those new to the forum - FAQs, Search Tips, Optimization, etc.

HDTV Frequently Asked Questions: Please read this before posting in the forum

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post #7 of 8 (permalink) Old 2011-03-15, 11:38 PM
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It turns out you were right I had the wrong settings in the BDP, so I fixed to bitstream for the digital output, and now when detecting dd5.1 the surround light turns on when the PL2 is off.

Now, I did the test again, set back the BDP to PCM 2ch and listened 10 min of prince of persia, then I set it back to bitstream and listened to the same 10 min; and I could not tell the difference regarding the surround effect, though, in PL2 the volume had to be on 32 specially for the SW, while in dd5.1 23 was more than enough.

However, even though I could not tell the difference, there is difference indeed; it is just that for me to be able to notice it I had to perform the test over again, but this time, I tried very very very hard to pay close attention and listen carefully specially at the surround speakers… and bingo! I finally was able to notice something different besides the volume level needed for the PL2 to sound like dd5.1.

When listening very close I finally noticed that in dd5.1 the separation is better (very clear difference between sounds, no background noise) for instance in a scene where horses are running, on dd5.1 only the wind of the desert can be heard from the rear speakers and the horses noise comes from the other speakers. On PL2 the wind comes from the surround speakers but listening carefully I was able to hear the horses noise as well on the background, very low but the sound is there, which means that the sounds are not totally separated, just the volume level are reduced in some of them to enhance the sound that is supposed to sound in the surround speakers.
Now if you ask me, I think that PL2 does a pretty good job "faking" the dd5.1, because, at least to my ears, I can tell the difference only if I'm focus hard to listen to the background sounds, and pay really close attention to the sounds separations, otherwise when focused on the movie I cannot notice it at all.
The only thing I have to do using PL2 is turn the volume higher, though, no too high because it seems that there is a point where the more volume you increase the more the background sounds are noticeable and then the fake dd5.1 is pretty evident an noticeable.

I don’t need to use PL2 because my receiver supports dd5.1, though, I would not mind to use PL2 if I need to. I don’t even will use it for the TV, because I'm getting a digital input splitter so I can have dd5.1 using both TV and BDP.
I guess if someone is too picky and is always looking for flaws, definitely will find them. But for some of us that are not that picky and can leave with some flaws in thinks, won’t be able to notice it. But that is just my opinion.
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post #8 of 8 (permalink) Old 2011-03-16, 12:02 AM
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While it is true that DPLII does a pretty good job of simulating the surround sound of actual DD5.1, that's no reason not to have the system optimized.

Additionally, you'll now know when the original programme is DD5.1 and not DD2.0.

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