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5.1 Surround downmix


christt

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Hello All,

Question about 5.1 surround sound.

I would like to know if I were to purchase a 5.1 system and only used a 3.1 system ( Left, Center, Right, Sub )  would the downmix sound bad? or would it work at all?  and anything else I should know before attempting this.

Thanks in advance.

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Personally, I think 3.1 is what makes sense for most people and their home viewing space. Marketing disagrees. 

 

Honestly, I think full surround sound even in a movie theater is kind of gimmicky depending on how it's used. 

 

Hate hearing discrete sound effects behind me somewhere. Always takes me out of the movie. But used to extend ambience, music or reverb I think is fine. 

 

 

 

 

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Poorly placed rears will sound worse than a good 3.1 setup.  In the down mix, a simplistic explanation of what will happen is that 5.1 surround / back material will use phasing to simulate surround out of the LR.  I think that most movies will not suffer from such a setup.  Basically you should buy the best speakers that you can.  There's nothing wrong with good old fashioned 2.0 setups.  The addition of a center channel is "power steering" that makes up for the poor placement of LR speakers, poor placement of listeners, or poor room acoustics, but doesn't add anything fidelity-wise if those factors are not an issue to begin with.

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Lt/Rt (Left total / Right total) stereo indicates two channels of program that exist as an encoded matrix of four to six discrete source channels. When decoded with Dolby® Pro-Logic, the two-channel matrix will play back as LCRS (left, center, right, surround). When decoded with Dolby® Pro-Logic II, the two-channel matrix will play back as LCRLsRsLFE (left, center, right, left surround, right surround, LFE). Lt/Rt, program material, whether encoded with 4, 5 or 6 source channels, should be compatible to decode with Pro-Logic or Pro-Logic II. Lt/Rt tracks are also designed to sound natural in a two channel monitoring environment (that is, as L/R stereo).

Additionally, any two channel stereo program that was originally intended to be played as Left/Right only, but that plays back appropriately decoded through Pro-Logic/Pro-Logic II, can be designated as Lt/Rt.

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On 1/19/2017 at 4:24 PM, VAS said:

Lt/Rt tracks are also designed to sound natural 

HA!

That completely depends on HOW the LtRt was created. I will only say this much now on this thread to avoid creating any more confusion, and more importantly a sudden void in the middle of all that is going on here. 

 

On 1/19/2017 at 4:42 AM, mikewest said:

Totally agree Derek surround info can sometimes be quite alienating.

But Tom surely L and R speakers are music and fx and the centre speaker is dialogue

as per the need for cinema patrons to hear dialogue from a centre source??

mike

the Center -- in an LR space is a GHOST center. created from equal amplitude, zero phase signals going to both L and R speakers. 

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3 hours ago, soundtrane said:

HA!

That completely depends on HOW the LtRt was created. I will only say this much now on this thread to avoid creating any more confusion, and more importantly a sudden void in the middle of all that is going on here.

All the "money" in post production is how the Lt/Rt downmix is done. Without any issues for DVD and broadcast screening / transmition.

:)

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But are not the L R channels intended for music and fx and significant dialogue put in Centre?

I guess this was learned when cinema and then DVD and TV needed to utilise Dolby surround.

It's a pity that Lester Koenig at Contemporary Records did not realise potential of a stereo center

image for his fantastic jazz recordings of 1958 so  his results are hole in the middle material.

mike

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We generally mix TV (esp docs) with music and FX in LR and surrounds, with dialog in the C--this is our daily-MO default.  However, theatrical feature films very often "diverge" dialog across the LCR somewhat, partly to not leave audience members sitting at the sides of a theatre feeling like the dialog is coming from far away (across the room in fact), but also because some directors want there to be a more spatial feeling to the dialog, ie a character that is on the left side of the screen has their voice coming  both from the C and from the L channels.  In animation this effect is even more pronounced.

Re: LtRt: although some networks still ask for it, some now specifically forbid it in place of LoRo (straight stereo): esp. USA PBS.  In general I find that hardly anyone is broad- or cablecasting LtRts anymore: they do Lo Ro or 5.1 and stereo listeners are hearing a downmix of the 5.1 done in their own equipment.  It used to be that we liked LtRt for festival use (could play fine as mono, stereo or decoded back to 5.1) but almost all the festivals I've sent mixes to in the last couple of years have gone to electronic delivery of DCPs, and they are getting mostly 5.1, or at least LCR.

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LtRt can cause weird sound in stereo playback (if not decoded) due to the sum of Ls and Rs being added to L and R with 180 deg phase inversion.

If you have the exact same signal in Ls as in L (but not Rs) this signal will not be played back in stereo mode without decoding first.

 

One more thing to consider in most home theater systems is that the subwoofer not only act as a real .1 (LFE channel) but also as a bass extension of your surround monitors. In a theater these monitors are fullrange, whereas at home, due to the small size of the monitors, the low frequencies are  routed to the subwoofer via bass management.

This means that the subwoofer is playing every bass content + additional LFE, which can overload the woofer driver at loud volume (creating harmonics).

Have you ever wondered why your HT sub is suddenly very loud in action scenes and you want to turn it down a bit? That's why ;)

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