dB Output of Center vs LR - AVS Forum
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post #1 of 17 Old 02-29-2012, 03:00 PM - Thread Starter
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I was wondering if anyone could direct me to a link with measurements of center speakers vs L&R. I have seen numbers like "70%" of the sound comes from the center", but I have never seen any data. Do they mean 70% of the content? 70% of the decibels? Any insight will be appreciated.

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post #2 of 17 Old 02-29-2012, 03:24 PM
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Originally Posted by Raul GS View Post

I was wondering if anyone could direct me to a link with measurements of center speakers vs L&R. I have seen numbers like "70%" of the sound comes from the center", but I have never seen any data. Do they mean 70% of the content? 70% of the decibels? Any insight will be appreciated.

There is no way to measure the % of sound that comes from the CC. It varies from movie to movie and from MC-music track to MC-music track. It depends on the mixer and the amount of dialogue and other sounds mixed in the CC. In many movies, especially dialogue heavy movies, there is a large

In terms of dB levels, the CC should be calibrated to the same level as the L/R's ad surrounds. Then, the amount of sound that comes out of the center channel speaker will be determined by the mix.

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post #3 of 17 Old 03-01-2012, 11:46 AM - Thread Starter
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Good points, very poorly stated in my part. Let's try again.

Regarding the first: In general, is there a range (% range) that is generally accepted as being true for most films (e.g. in +80% of films 60-80% of the sound comes from the center, and if separate data is available for music, great).

Regarding the second: generally speaking, is there a preponderance by recording engineers in movies and music BR/DVDs to run the center channel hot in relation to the L and R channels (i.e. is there any generalized data that could be expressed in the same manner as the above example).

Thanks

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post #4 of 17 Old 03-01-2012, 12:14 PM
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Originally Posted by Raul GS View Post

Good points, very poorly stated in my part. Let's try again.

Regarding the first: In general, is there a range (% range) that is generally accepted as being true for most films (e.g. in +80% of films 60-80% of the sound comes from the center, and if separate data is available for music, great).

Regarding the second: generally speaking, is there a preponderance by recording engineers in movies and music BR/DVDs to run the center channel hot in relation to the L and R channels (i.e. is there any generalized data that could be expressed in the same manner as the above example).

Thanks

NO idea on your first question. If the second question is "do mixing engineers calibrate the center hot?" the answer is "no" at least for movies. THere's a standard calibration that all mixing stages use - with a -20dBFS band limited pink noise tone, each of the left right and center will be 85 dB from the mixing position.

There are not rules for music production, but I cannot imagine why the mixers would calibrate the center hot - it's a guaranteed way to make your mulitchannel mix sound incorrect wherever you play it other than in the specially tweaked mixing/mastering studio. Most mixers are trying to get a mix that sounds good in various venues, not one that fails once it's taken outside one particular studio's walls.

If your second question is just a rephrasing of the first - "do they put a quantifiable amount more into the center than left and right (assuming equal calibration)" IDK the answer to the question either way it's phrased.
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post #5 of 17 Old 03-01-2012, 02:29 PM - Thread Starter
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No, the second question is what you assumed. I was just trying to make sure I'm not making any assumptions so I was trying to flesh out both options. Some people seem to throughout stats with regards to the differences between C vs L&R, and I was just trying to get any quantifiable data that may be available.

Thanks

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post #6 of 17 Old 03-01-2012, 03:26 PM
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Originally Posted by Raul GS View Post

No, the second question is what you assumed. I was just trying to make sure I'm not making any assumptions so I was trying to flesh out both options. Some people seem to throughout stats with regards to the differences between C vs L&R, and I was just trying to get any quantifiable data that may be available.

Thanks

Here's an experiment you can try with movies. LEave your system set up for a "live" center, then unplug your center. See how much of the movie's (or mivies' if you want to test several) sound is missing. I did this by accident by incorrectly setting up a new center one time. I happened to have Jaws playing. People on the screen were yelling and running, but in my room it sounded like one of those put-you-to sleep wave sound machines. There was literally nothing but waves crashing and maybe an occasional bell in any channel but the center . . . .
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post #7 of 17 Old 03-01-2012, 06:15 PM - Thread Starter
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Interesting I'll have to try it some time. However. I was hoping there may be some actual data available.

Thanks

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post #8 of 17 Old 03-02-2012, 05:58 AM
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Originally Posted by Raul GS View Post

Interesting I'll have to try it some time. However. I was hoping there may be some actual data available.

Thanks

Would be interesting to see but I don't know who would be motivated to do it. Somewhat obviously the relative contribution of different speakers changes constantly so you'd have to decide how to weight any average and whatever approach you chose folks would disagree with. More importantly to me it does not affect equipment requirements. Although the left speaker may usually carry a third of the spl of the center there are occasions when sound in that speaker is at or near 0dBFS, as loud as it can get, 105 dB at reference level. So I need all the speakers to be able to play those peaks even though 80% or more of the time it is the center carrying most of the load.
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post #9 of 17 Old 03-02-2012, 07:57 AM - Thread Starter
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Yeah, I figured I most likely was not going to be able to get any data, but also thought there would be no harm in trying. Thanks for everyone's input.

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post #10 of 17 Old 03-20-2012, 10:05 AM
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For Casino Royale, I've had just the front two channels running, and then just the center running.

Surprisingly, some scenes had had more music and effects in the FL and FR, and other scenes, like the opening black-and-white one, had more in the center.

Dialog, pistol sound sound effects like chambering a round, gun shots, the smashing of a skull onto a sink, crashing through a wall, etc. all were in the center.

Further testing could involve REW's SPL Meter Logging Mode, where you see a running graph of peak output over time. One could compare the same sequence in each setup, without sub, to see where the peak levels of the gun shot, explosion, etc. occurs. If the center was 3dB over the FL speaker, for instance, you could say that it has twice the level of content for that sequence.

That's nothing definitive, of course, as it's a small sample size, and your own speaker and room acoustics are playing a part. I suppose you could subtract out that channel's known variance from "flat" to only judge the relative sound track material contribution.

Better analysis would be using the same waterfall-making-software people use for the pretty LFE waterfall movie charts of peak output at what time at what frequency. It'd just be a matter of changing the channel from LFE to Center, FL, FR. I've started to play around with this but as I am new to making those waterfalls, it's a painful process, and I have no good data as a result.

Maybe there's an Audio Engineering Society paper on this. I have read, for instance, papers studying the dynamic range of all different genres of music, in the context of whether amplifiers can be used with lower RMS ratings but higher dynamic headroom (conclusion: most music peaks were under 200ms, so for those on a budget, dynamic headroom duration of 200ms can be used, but to handle worst case scenarios of 2 seconds, one should just look to the RMS rating).

Regardless, doing this kind of stuff emphasized for me that for 5.1 channel films, it's silly to have an anemic center speaker. If the center has to be different than the other two speakers, it would ideally be MORE capable!
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post #11 of 17 Old 03-20-2012, 01:53 PM - Thread Starter
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Originally Posted by Eyleron View Post

Maybe there's an Audio Engineering Society paper on this.

That is what I was hoping someone could direct me to. Although the DIY option you provide is interesting, is more work than I wanted to do (thus my hope for a peer review paper).

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Regardless, doing this kind of stuff emphasized for me that for 5.1 channel films, it's silly to have an anemic center speaker. If the center has to be different than the other two speakers, it would ideally be MORE capable!

Therein lies the irony, far too often the CS seems to be the less capable.

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post #12 of 17 Old 03-20-2012, 02:21 PM
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A center speaker should only be less capable in the lowest frequencies -- those frequencies where the directionality of the sound is not obvious to the listener. If it's less capable in other ways, you purchased the wrong center speaker. The best center speaker would be identical to your L&R front speakers, but that's usually impossible due to placement requirements. You do need to make sure its crossover frequency is set high enough in your surround-sound processor that its bass gets properly redirected to a subwoofer, or to the fronts, if they're "full range" speakers. (I put "full range" in quotes because a dedicated subwoofer will be able to produce far better low frequencies than the vast majority of front speaker designs.)

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post #13 of 17 Old 03-20-2012, 02:57 PM
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Originally Posted by Raul GS View Post

In general, is there a range (% range) that is generally accepted as being true for most films (e.g. in +80% of films 60-80% of the sound comes from the center, and if separate data is available for music, great).

Never thought about it in terms of how much content comes from the centre, but instead what content comes from the centre.

In my experience, the most critical elements of the recording are usually mixed to the centre. For movies, that means dialogue, which is the most important piece of audio when it comes to following the story. But even with 2-channel music, lead vocals and instrument solos are typically mixed to the centre (centre of the soundstage, not a discrete centre channel obviously).

With that in mind, I don't see why anyone would want to reproduce those critical elements using a less capable centre speaker (let alone rely on a phantom centre).

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post #14 of 17 Old 03-20-2012, 06:38 PM
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Originally Posted by Eyleron View Post

For Casino Royale, I've had just the front two channels running, and then just the center running.

Surprisingly, some scenes had had more music and effects in the FL and FR, and other scenes, like the opening black-and-white one, had more in the center.

Perhaps these scenes were mixed by different people...or one very mixed-up person....

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Originally Posted by Eyleron View Post

Regardless, doing this kind of stuff emphasized for me that for 5.1 channel films, it's silly to have an anemic center speaker. If the center has to be different than the other two speakers, it would ideally be MORE capable!

Exactly, at least if home theater is valued as much as 2-channel music, and even if it isn't, then maybe a phantom center would work better for some systems--basically, either use an adequate center speaker or take it out.

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Never thought about it in terms of how much content comes from the centre, but instead what content comes from the centre.

In my experience, the most critical elements of the recording are usually mixed to the centre. For movies, that means dialogue, which is the most important piece of audio when it comes to following the story. But even with 2-channel music, lead vocals and instrument solos are typically mixed to the centre (centre of the soundstage, not a discrete centre channel obviously).

There are movies, though, that image dialogue between two of the front channels, and there are even some mixes that place dialogue in all three front channels at once. It's weird, but I've seen (and heard) it. There was even one title (I might be able to recall which if I thought about it hard enough) I've seen that has ONLY dialogue in the center channel, no effects and no music (even the center-imaged effects and vocals of songs are only in the left & right channels)--unusual to be sure. In addition, some movie soundtracks place the score firmly in the front stage, while others place much of it in the surrounds. Over time, the variety of mixing styles appears to have diversified, which probably means that mixers are experimenting more, no longer being bound by tradition to the limitations of the Dolby Stereo matrix. That's why I try to make sure that ALL of my speakers are up to snuff, even the surrounds--they don't all have to be identical, but they should all be pretty good, and should image well with one another (you know it's right when the individual speakers seem to "disappear" into a cohesive surround soundstage when playing a well-mixed soundtrack).

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Originally Posted by sdurani View Post

With that in mind, I don't see why anyone would want to reproduce those critical elements using a less capable centre speaker (let alone rely on a phantom centre).

Phantom centers have always worked fine for me when I've used them in the past.
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post #15 of 17 Old 03-20-2012, 07:11 PM
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Originally Posted by Robert Cook View Post

There are movies, though, that image dialogue between two of the front channels, and there are even some mixes that place dialogue in all three front channels at once. It's weird, but I've seen (and heard) it.

There are soundtracks with steered dialogue, but it isn't common.
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There was even one title (I might be able to recall which if I thought about it hard enough) I've seen that has ONLY dialogue in the center channel, no effects and no music (even the center-imaged effects and vocals of songs are only in the left & right channels)--unusual to be sure.

Unusual to have ONLY dialogue in the centre speaker, but not unusual to have song vocals in the L/R channels, since songs in movie soundtracks are typically sourced from 2-channel recordings.
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Over time, the variety of mixing styles appears to have diversified, which probably means that mixers are experimenting more, no longer being bound by tradition to the limitations of the Dolby Stereo matrix.

There are rare exceptions, but my point was that as a rule, the most critical elements of a recording (movie or music, stereo or multi-channel) are mixed to the centre: either the discrete centre channel of a 5.1 soundtrack, the matrixed centre channel of a Dolby Surround mix, or the phantom centre channel of stereo music mix (the latter two can be extracted to a centre speaker).
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That's why I try to make sure that ALL of my speakers are up to snuff, even the surrounds--they don't all have to be identical, but they should all be pretty good, and should image well with one another.

Agreed. I don't think anyone is advocating a centre speaker that is more capable than the L/R speakers, but rather moving away from the all to common use of less capable centre speakers. Doesn't have to be identical, though I ended up that way (was the cheaper and lazier solution).
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Phantom centers have always worked fine for me when I've used them in the past.

Sure, but the question is whether you can do better. Remember, "stereo" was originally intended to be 3 channels.

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post #16 of 17 Old 03-20-2012, 08:33 PM
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Originally Posted by sdurani View Post

There are soundtracks with steered dialogue, but it isn't common.

It's still uncommon, that's true, but I own several DVD/BD titles (mainstream, mixed by known mixers such as Gary Rydstrom) that noticeably have steered dialogue, almost certainly by the preference of the individual director, I would think. I literally stuck my head between the speakers to verify what I was hearing, so I'm reasonably certain. My point here was to stress the importance of timbre-matching and having good imaging all across the front.

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Unusual to have ONLY dialogue in the centre speaker, but not unusual to have song vocals in the L/R channels, since songs in movie soundtracks are typically sourced from 2-channel recordings.

That's true, too, although it seems--at least in my personal experience--that many songs are remixed to include the center channel, which kind of surprises me, actually.

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There are rare exceptions, but my point was that as a rule, the most critical elements of a recording (movie or music, stereo or multi-channel) are mixed to the centre: either the discrete centre channel of a 5.1 soundtrack, the matrixed centre channel of a Dolby Surround mix, or the phantom centre channel of stereo music mix (the latter two can be extracted to a centre speaker).

I agree, and didn't mean to contradict anything you said (we're on the same side here). I guess my point was that just about anything goes these days, and ideally one's system could handle anything that soundtracks can throw at them, even if it's non-traditional from a certain point of view. To take another example, I've even encountered (during testing) soundtracks that put so much mid-bass into the surround channels that some things around the room were rattling even with the subwoofer turned off and bass management still running --this was when I decided that having capable surrounds was a good idea, even if they would only occasionally be needed, and it paid off when I started to encounter soundtracks that, as mentioned previously, place much (if not most) of the musical score in the surround channels. Admittedly, I had initially misjudged how the surround channels would eventually be used (at least sometimes), despite knowing that they were full-range channels in the then-new discrete digital formats.

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Agreed. I don't think anyone is advocating a centre speaker that is more capable than the L/R speakers, but rather moving away from the all to common use of less capable centre speakers.

It has been good to see reality gradually replace more hidebound views over the years in this respect. When I started out in home theater, around 17 years ago, the vast majority of people seemed to believe that only dialogue ever came out of the center speaker (like in the rare example I gave), and that the left & right front speakers (or the "mains") handled the bulk of the work, but that was never generally true, especially with Pro Logic (so obvious and easy to detect, yet so hard to accept!). Convincing them of this was almost as difficult as convincing them that their tower speakers should be set to "Small," although people seem to have largely gotten over the latter by now.

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Doesn't have to be identical, though I ended up that way (was the cheaper and lazier solution).

I did, too, and as soon as I installed my identical surrounds (first time I had a fully-matched set), I thought they weren't working at times! Nothing was ever wrong with the soundtracks, I just wasn't aware of the speakers, per se, anymore. I had figured that imaging would indeed be closer to seamless, but I didn't expect to hear that huge of a difference due to the fact that the surround speakers were all the way across the room from the fronts, on either side of me. I kept rechecking the levels for a while, even though everything sounded great.

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Sure, but the question is whether you can do better. Remember, "stereo" was originally intended to be 3 channels.

That's right, especially for off-axis viewers--a bigger issue for commercial movie theaters than most home theaters, but still an issue. It's just that some folks have such awful accommodation for their center speakers (e.g. boxed inside a shelf or with a huge height differential from the other front speakers) that they're probably better off compromising with a phantom center. Whatever the theory may be, in practice I find that having front speakers at significantly different heights bothers me more than putting up with a phantom center. That's why my current system has all of the front speakers at the same height, even though this means that they're all slightly above the TV screen--that's the best overall compromise for me, at least.
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post #17 of 17 Old 03-21-2012, 12:34 PM
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Quote:
Originally Posted by Robert Cook View Post

mixed by known mixers such as Gary Rydstrom

Yeah, that's where I've noticed steered dialogue mostly, on Pixar titles; some old movies too (e.g., Bad Day at Black Rock).
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That's right, especially for off-axis viewers--a bigger issue for commercial movie theaters than most home theaters, but still an issue.

Actually, I was thinking of the early 1930s, when Bell Labs was inventing "stereo" (from the Greek 'sterios', meaning solid/3D). They concluded that the minimum needed to create a realistic wavefront was 3 channels/speakers up front (and that doesn't even include realistic reproduction of ambience).

All of Bell Labs' research had to do with music reproduction at home, not movies in commercial theatres. BTW, the first movie to use 3 speakers across the front was Disney's 'Fantasia', which is almost completely music with a handful of lines of dialogue.

While centre speakers are typically seen as advantageous for off-axis viewers, there are also advantages for the listener in the sweet spot. The human voice is not a dual-mono, phantom-imaged, comb-filtering source. Since we don't hear it that way in real life, why should we deliberately reproduce it that way at home?
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It's just that some folks have such awful accommodation for their center speakers (e.g. boxed inside a shelf or with a huge height differential from the other front speakers) that they're probably better off compromising with a phantom center.

Agreed, that's about the only time I ever suggest a phantom centre, when the difference in height is the bigger compromise.
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Whatever the theory may be, in practice I find that having front speakers at significantly different heights bothers me more than putting up with a phantom center. That's why my current system has all of the front speakers at the same height, even though this means that they're all slightly above the TV screen--that's the best overall compromise for me, at least.

That's how I ended up as well, with all 3 front speakers at the same height. Would've loved to have placed them at ear height (around 36"), but compromised by placing them above TV height (about 40" off the floor). I did orient them upside down, to get the tweeters as close to ear height as possible.

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