# Stereo audio through "surround" speakers?



## cpf (Jan 14, 2011)

So, I'm handling the technical details for a fairly important film festival happening soon, and am encountering some issues with the (surround) sound.

The space has a surround-sound setup with 1 center, L/R front and L/R back channels. Due to the way the system is configured, the only time the back channels are used is when you've got a surround-sound disc in the BD player, which is linked digitally (coax) to a Crestron surround sound processor of some type, which is then wired to the amplifiers. 

Now, this works great when the disc is surround-sound enabled, but after a recent test session it appears the upcoming films being shown are in stereo. The way the system is set up now sound is only sent to the Center and L/R front channels, leaving a definite aural hole "behind" the viewer's head (394 seats).

So, my question is, is this how "surround sound" is supposed to work, with stereo audio only being routed to the front speakers, leaving the back ones unused? If, let's say on the day-of the picky film people decide they want "more sound" even if it isn't "surround sound," is there a way to configure the (Sony BDP-S500) BD player to route the stereo L/R from the DVD to the back "surround" channels, too? 

I'm hoping the test DVD I had was mixed down to stereo just for convenience and the actual films will arrive with all 5.1 channels of sound, but I'd thought I'd post this just in case.


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## museav (Jan 15, 2011)

cpf said:


> Now, this works great when the disc is surround-sound enabled, but after a recent test session it appears the upcoming films being shown are in stereo. The way the system is set up now sound is only sent to the Center and L/R front channels, leaving a definite aural hole "behind" the viewer's head (394 seats).
> 
> So, my question is, is this how "surround sound" is supposed to work, with stereo audio only being routed to the front speakers, leaving the back ones unused? If, let's say on the day-of the picky film people decide they want "more sound" even if it isn't "surround sound," is there a way to configure the (Sony BDP-S500) BD player to route the stereo L/R from the DVD to the back "surround" channels, too?


Stereo is by definition two channels, so if they produced the audio in stereo then it would probably best be reproduced through just the main left and right channels. It could also be that it is in 5.1 surround but there may intentionally be nothing in the surround channels. Typically the concept for cinemas is to create a playback environment that matches the production and mastering environment so that the audience hears what the production team wanted them to hear. So for a film festival it seems to make sense to try to reproduce what the production team wanted to be heard.

One thing you may want to check is that the Blu-Ray player does have settings for downmixing Dolby Digital and DTS signals, so you may want to verify that Dolby Digital and DTS are not being downmixed to Linear PCM.

Many surround sound processors do offer operating modes that allow for different signal routing such as modes that mix the audio and send it to all outputs. I've had clients who wanted to use that, at least until they heard it. It is nice if you're having a party and want the people wandering around to hear the same thing from every speaker but that is about the only good use for it. There may also be a mode that synthesizes surround or 5.1 information from a two channel signal. If so that may be an option, although it may also be varying from the original intent.

A bit off subject, but the Sony BDP-S500 is a consumer product and the warranty specifically excludes commercial use, so it's a rather interesting choice for use in a 349 seat venue.


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## iccelou91 (Jan 15, 2011)

We'll see if anyone disagrees with me but: if it isn't in surround you probably shouldn't be messing with it. I say this for a few reasons:

1. Remixing the sound is modifying someone else's work without their permission. If it is given to you in stereo it's probably meant to be in stereo.

2. If you just send the same signal to all the speakers you're going to end up with delay problems and probably phase cancellation.

3. If people want "more sound" you can give it to them in stereo. Turn up your amplifiers or (if necessary) add more FOH speakers.

It doesn't seem to me that everything needs to be in 5.1... 2.1 isn't really that awful.


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## cpf (Jan 15, 2011)

Thanks for the input. These are outdoor adventure films, and the local rep noted that the sound was loud enough, but in the back 1/2 of the seating the sound is quite clearly coming from the screen area (as opposed to surrounding the listener) and that, given the genre, a surround "experience" would make more sense. I checked the DVD and confirmed everything was in stereo or mono (most likely due to the production challenges with helmet cams and waterproof cases), but I wasn't sure how this was supposed to be handled.

Yes, it's unfortunate that the player I have to use is very consumer, the organization got sold a bill of goods by a sketchy installer that left town minutes after they got their last payment, etc, etc. Short story is it's nearing a disaster, but it's what's we have.

I think I'll try manually patching the rear LR channels to match the forward ones, just to see how it sounds for all the areas around the seating area.


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## WooferHound (Jan 15, 2011)

cpf said:


> a Crestron surround sound processor of some type, which is then wired to the amplifiers.


 
You need to find out more about the Crestron Audio processor. It should have different modes to make it work like you want it to. There are some Home Theater people on this forum that can help you out a lot with theater sound.
Home Theater Forum and Systems - HomeTheaterShack.com


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## avare (Jan 15, 2011)

There are at least two issues involved. One is the artisitc changing of the sound aspect of the film. If it is a serious film festival, this is a big no-no.

Second is the sound stage appears (sonically of course) to envelop the listener at the front half of the venue, something is very wrong cinematically. 2.1 and 3.1 systems PROPERLY SETUP have the left/right speakers behind the screen, or as close as practically possible if perf scren is not used.

If you still choose to persue it, if you can not get specs on the controller, then patch in betwen the line outputs of the processor and amplifiers.

Let us know how things turn out and good luck!

Andre


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## iccelou91 (Jan 15, 2011)

> Thanks for the input. These are outdoor adventure films, and the local rep noted that the sound was loud enough, but in the back 1/2 of the seating the sound is quite clearly coming from the screen area (as opposed to surrounding the listener) and that, given the genre, a surround "experience" would make more sense. I checked the DVD and confirmed everything was in stereo or mono (most likely due to the production challenges with helmet cams and waterproof cases), but I wasn't sure how this was supposed to be handled.


If the filmmakers intended for it to be mixed in 5.1, they would have mixed it in 5.1. Your job is not to mix sound for the film, it is to (to the best of your ability) recreate the original mastering of the film.


> I think I'll try manually patching the rear LR channels to match the forward ones, just to see how it sounds for all the areas around the seating area.


It will sound... bad. Running the same signal out of front-facing and rear-facing speakers creates problems because the time it takes for the signal to reach a member of the audience will be different unless they are sitting equidistant from all speakers, but that won't be everyone. These delays can also create comb filtering. If the signal is degrading too much by the time it hits the rear of house, the solution is putting. in another layer of front channels, not using rear channels.

EDIT: Not comb filtering. Just phase cancellation.


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## mstaylor (Jan 15, 2011)

Is it possible just to put in a small delay to reinforce the front experience that way it stays stereo but doesn't lose impact in the rear. 
Not being a sound expert like some here, I don't really understand how you be having that much of a dropout in a sub 400 seat house.


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## Anonymous067 (Jan 15, 2011)

iccelou91 said:


> 1. Remixing the sound is modifying someone else's work without their permission. If it is given to you in stereo it's probably meant to be in stereo.



Hmm. Interesting, I haven't heard this before. What about changing the volume? If I play a movie at a different volume on my TV, is that modifying their work too? It's not like you can just "create" a surround channel (to clarify, I mean by physically moving channels from the LR to the surround...). If its in the LR, it's always going to be there...unless you call up the original engineer and have him change it...(sarcasm).


iccelou91 said:


> 2. If you just send the same signal to all the speakers you're going to end up with delay problems and probably phase cancellation.


 
Easily correctable with correct deployment, engineering, and the proper processing.
However, it probably is a bad idea, because surround channels usually hold...well...surround sounds. Not the main voices of the people you're watching in front of you. It would be weird to watch a movie in front of you with the voices behind you...


iccelou91 said:


> 3. If people want "more sound" you can give it to them in stereo. Turn up your amplifiers or (if necessary) add more FOH speakers.


 
Be careful where you add those FOH speakers. That could just as easily add delay and phase issues. Unless you know how to deploy line arrays correctly...or have the $ to hire the pros to do it, don't just go around adding speakers on sticks everywhere...


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## WooferHound (Jan 16, 2011)

cpf said:


> These are outdoor adventure films, and the local rep noted that the sound was loud enough


 
If the Local Rep likes it, then why are you trying to fix it ?


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## iccelou91 (Jan 16, 2011)

Anonymous067 said:


> Hmm. Interesting, I haven't heard this before. What about changing the volume? If I play a movie at a different volume on my TV, is that modifying their work too? It's not like you can just "create" a surround channel (to clarify, I mean by physically moving channels from the LR to the surround...). If its in the LR, it's always going to be there...unless you call up the original engineer and have him change it...(sarcasm).
> 
> 
> 
> ...



I thought about not even answering this because it is painfully condescending, but I'll try to keep it civil:

1. Obviously adjusting volume and matching L/R to your system are fine. If you're talking about remixing the audio of a film from stereo into surround it's entirely different. This would be a much more substantial change, and IMO it would be unacceptable and possibly illegal. No one has actually suggested that, but at the time I thought they might.

2. Here's what I was thinking: There is no way to correct for a delay for speakers facing in opposite directions because the signals will run over each other, adding a delay would only change the place where the signals meet, but because they would still be travelling in opposite directions they could still interfere with each other.

3. I was not suggesting that throwing speakers at the system randomly would solve anything. I have no idea why you inferred that, but I find it insulting. Anyway, if the problem is an uneven distribution of sound through the house, I think we can agree that the FOH is less than ideal.

Please try not to tell me I am wrong when you have simply misunderstood my post. It is not necessary to be so condescending.

EDIT: museav confirmed my thoughts on phase cancellation were indeed correct.


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## museav (Jan 16, 2011)

Anonymous067 said:


> Hmm. Interesting, I haven't heard this before. What about changing the volume? If I play a movie at a different volume on my TV, is that modifying their work too? It's not like you can just "create" a surround channel (to clarify, I mean by physically moving channels from the LR to the surround...). If its in the LR, it's always going to be there...unless you call up the original engineer and have him change it...(sarcasm).


Cinema audio, and video, is very different than live performance in that it is about accurate reproduction and not creation. In the cinema world there are standards for just about everything from ambient light levels and image brightness to audio level. Now I'm not saying that every cinema complies with every standard but the goal of many of them is to have every audience receive the same intended result. One aspect of this is that the frequency response of human hearing varies with level, so vary the level from that intended and what is heard will be different from what was intended. 


Anonymous067 said:


> Easily correctable with correct deployment, engineering, and the proper processing.
> However, it probably is a bad idea, because surround channels usually hold...well...surround sounds. Not the main voices of the people you're watching in front of you. It would be weird to watch a movie in front of you with the voices behind you...


The resulting interference issues from multiple speakers in different locations reproducing the same signal cannot be corrected. You may be able to be optimize it for a listener but as the relative phase and levels of the multiple sources will vary throughout the listener area, any change to improve one location can make another worse. All you could do is try to find the best compromise, but there is no way to actually correct for it for all listeners.


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## iccelou91 (Jan 16, 2011)

museav said:


> The resulting interference issues from multiple speakers in different locations reproducing the same signal cannot be corrected. You may be able to be optimize it for a listener but as the relative phase and levels of the multiple sources will vary throughout the listener area, any change to improve one location can make another worse. All you could do is try to find the best compromise, but there is no way to actually correct for it for all listeners.


 
Oh good, I'm not crazy.


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## museav (Jan 17, 2011)

iccelou91 said:


> 2. Here's what I was thinking: There is no way to correct for a delay for speakers facing in opposite directions because the signals will run over each other, adding a delay would only change the place where the signals meet, but because they would still be travelling in opposite directions they could still interfere with each other.


Getting way off topic here, but while interference of multiple sources could be an issue, that interference is a result of the relative phase and level between the signals that then affects the resulting frequency response. Since the relative phase and level of the signals would be dependent upon the physical relationship of the receiving point to the sources, they would vary throughout the listener area. You could pick a listener location and optimize for it via delay, etc. only to potentially increase the problems at other listener locations.

If the variations in relative time arrival of the signals, which is what causes the differences in phase, were to become long enough they might cease being interference issues and become localization and intelligibility issues.


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## cpf (Dec 23, 2011)

Just got the rider for the 2012 edition of this event, and thought I'd follow up this. We went with normal stereo, and no one complained in-person or online, so it must have been good. Strangely enough they're still specifying 5.1 on the rider, but maybe this time the films will actually be using it.


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## mstaylor (Dec 26, 2011)

I have found that many times riders get written but the road guys have no idea what's in it, especially in recurring shows. I did a theatre productions a few weeks ago and the points were different in the rider than what they needed. It didn't create a big problem, but the rigger said it called for a point to be a couple of feet up from where I put it. He said Iput it where his intruss 1/4 ton was.


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## avkid (Dec 26, 2011)

mstaylor said:


> I have found that many times riders get written but the road guys have no idea what's in it, especially in recurring shows.


 If we get a correct rider, it's almost a miracle.


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## Robert (Dec 26, 2011)

I've had to handle two types of riders. One that is factual and accurate and the other that is some wish list created by who knows asking for the things that hey thought might make the act look or sound better. The real joke is, most of the time if you let the local provider know what your doing and how much money you can spend, you get better gear. In my opinion.


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