Dumb (probably) question about dolby sound

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robjg63

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#56870 27-Jan-2010 10:04

Hi - I have finally splashed out and got a home theatre to go with the big screen.

A Denon AVR-590 for the record.

I hooked it up with optical audio from the TV and watched the Bruce Willis movie (Die Hard?)on tv3 on monday night - I had the TV set up to select the dolby stream if available, and the movie was marked as 5.1 surround.

Sure enough the rear speakers occasionally burst into life with gunshots etc and the sub woofer went crazy on the explosions. So it seemed good to me. The amp displayed Dolby - all was good.

Watched something on tv4 last night (How I met your mother) which is not Dolby (only tv3 use this right?) and the rear speakers were working with music etc.

Flicked back to TV3 and watched House - the dolby stream was selected and not a peep out of the rear speakers for the whole program. The program is not advertised as 5.1 surround or anything. Flicked it to the 'other' audio stream and the back speakers were noticeably busy on that.

So my (dumb) questions are:

There is dolby and the 'other' stream - sorry - I didnt note the right acronym and only tv3 have the 2 different streams.

1) TV3 are the only ones that have a 'dolby' stream available?

2) Can the 'other' stream support 5.1 surround or is this just the Dolby stream as I suspect?

3) If you have the dolby stream selected and they have a program with just presumably stereo audio I might expect the back speakers to be doing nothing?

4) Switching to the 'other' stream means that the front and rear left speakers will be putting out the same audio (likewise the right side speakers)?

Any advice happily accepted...

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gcorgnet

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#293300 27-Jan-2010 10:12

I am no expert but it seems to me that when watching Die Hard, your HT was getting 5.1 and was outputing it correctly.
Then you switched to C4 and the HTwas getting 2 channels only but still used surround speaker for the music (it would be like 'artificial' 5.1 if you like)
There might be a setting on your HT to specify whether the HT should try and output surround sound, even if it doesn't receive any signal for these speakers.
What I think happened with House is that the HT was receiving 5.1 sound from TV3 (therefore the HT was not trying to artificially output anything on the surround speakers) but there was simply no sound to be played on the speakers (It's not like House is really action-packed and full of gunshots and explosions...)

Again, I am no expert so maybe someone else can confirm/correct this.
In the meantime, I hope this helps.

Guillaume

Jaxson

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#293311 27-Jan-2010 10:42

If the source is 2 channel (TV 4 for instance, or playing a CD) then you can chose to let the amplifier play this as 2 channel (front left and right speakers only) or it can simulate a surround sound effect from the 2 channel source and play some sounds out all the speakers.

If the source is 5.1 sound then your amplifier will play through all speakers.

The one proviso/trap is that TV3 on terrestrial freeview has a 5.1 sound track, but when the source program is only two channel it will only play out the left and right speaker, EVEN THOUGH your amplifier will be showing a dolby symbal or 5.1 or something like that.

Hope that clears that up for you.

Oblivian

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#293313 27-Jan-2010 10:43

Yep thats Pretty much the jist of it.

5.1 TV Eps: Don't expect too much action in the back speakers.
5.1 Movies: Often lots of surround stuff, traffic passing by etc etc

Dolby Stereo Stream: Depends on your AMP, if you have it in AFD/(auto format decode) it may only turn to stereo, you might have to adjust it to be Pro Logic I/II to get a bit of rear phasing

AAC (everyone not TV3) is more or less a Pro Logic stream, so often a bit at the rear.

Have a fiddle and see if you can put a normal program on 3 into pro-logic mode, it should get over written when there is a true 5.1

/edit Aww beaten!

robjg63

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#293320 27-Jan-2010 11:00

Sweet - thanks for your replies.
Sounds like I need to find a setup option (maybe if it exists) that says if the program isnt surround 5.1 Dolby, then fudge it to stereo.

I'd swear that Home theatre is more mind boggling than anything else I have bought for ages. So many acronyms/varying standards and ways of doing things etc. and thats not counting the cables!

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sbiddle

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#293329 27-Jan-2010 11:15

robjg63: Sweet - thanks for your replies.
Sounds like I need to find a setup option (maybe if it exists) that says if the program isnt surround 5.1 Dolby, then fudge it to stereo.

I'm not sure what you mean by this. TV3 transmit in AC3 5.1 fulltime. If the show is 5.1 you'll get sound out of all speakers. If it's stereo you'll get audio from the Front L and Front R speakers but the stereo feed is contained within a 5.1 wrapper.

If you were getting sound from all speakers on C4 you had some form of audio processing set on your amp. All channels except TV3 are only broadcast in 2ch stereo so you should only have sound from the Front L and Front R speakers.

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#293362 27-Jan-2010 11:44

your amp should display the signal sent to it from the tv. you should be able to tell if you are getting 5.1 or 2.0 sound (which obviously gets processed into a 'fake' 5.1 by your clever amp)

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robjg63

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#293364 27-Jan-2010 11:47

sbiddle:
robjg63: Sweet - thanks for your replies.
Sounds like I need to find a setup option (maybe if it exists) that says if the program isnt surround 5.1 Dolby, then fudge it to stereo.

I'm not sure what you mean by this. TV3 transmit in AC3 5.1 fulltime. If the show is 5.1 you'll get sound out of all speakers. If it's stereo you'll get audio from the Front L and Front R speakers but the stereo feed is contained within a 5.1 wrapper.

If you were getting sound from all speakers on C4 you had some form of audio processing set on your amp. All channels except TV3 are only broadcast in 2ch stereo so you should only have sound from the Front L and Front R speakers.

OK - that makes sense. So AC3 5.1 is the Dolby stream?

AAC = stereo

Perhaps my musings didnt quite make sense......

So - as House was just stereo there was no rear speaker tracks - that makes sense and was what I thought was probably the case. Everything else (the other channels) are stereo only and my amp should have probably left the rear speakers off.

So I'm probably looking for an option that says if there is no audio stream for the back speakers (ie 2 channel audio being received) - whether that be via AAC or dolby, then put the sound for the left channel to the front and back left speakers and ditto for the right side. Otherwise - if its coming in in 5.1 surround just let it do its stuff.

Bound to be an option for that - just a matter of finding what they called it ;-)

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sbiddle

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#293379 27-Jan-2010 12:09

Some amps can let you mess with a AC3 feed and, many won't. You are hearing it as it's supposed to be heard.

If you want to run it through the processor and do something like a matrix you may find you'll need to switch your STB to the AAC feed which will give you 2ch stereo.

richms

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#293696 27-Jan-2010 23:03

the AAC feeds are also vastly inferior to the AC3 feed qualitywise.

Richard rich.ms

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#296661 6-Feb-2010 19:53

An aside I thought I read on one of these forums somebody from TVNZ saying their two channel AAC feeds are actually encoded in Dolby PrologicII so that if you apply the DPL processing to them, you will actually get rear channel information.

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#296670 6-Feb-2010 21:27

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robjg63

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#296678 6-Feb-2010 22:55

This thread :http://www.geekzone.co.nz/foru...

Nothing is impossible for the man who doesn't have to do it himself - A. H. Weiler