Do 115 dB peaks on the LFE channel represent what you hear in a movie theater? - Page 4 - AVS Forum
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post #91 of 131 Old 08-23-2009, 03:45 PM
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Quote:
Originally Posted by sivadselim View Post

Could y'all all just go watch a movie or something like that, maybe?

What... you're not enjoyin' the love-fest?

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post #92 of 131 Old 08-25-2009, 06:52 AM
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Quote:
Originally Posted by J_Palmer_Cass View Post

Only use three main channels plus the LFE channel for this 120 dB SPL PEAK output calculation.


Link to Dolby on LFE


"The LFE channel carries additional bass information to supplement the bass
information in the main channels. The signal in the LFE channel is calibrated
during soundtrack production to be able to contribute 10 dB higher SPL than the
same bass signal from any one of the screen (front) channels. Even if all three
screen channels are active, enough bass could be delivered by the LFE channel
alone to bring the theatre’s subwoofer into acoustic balance with the screen
channels. This allows filmmakers to unburden the main channels by diverting the
strongest bass to the separate LFE channel, as needed. Under the most demanding
program conditions, where the bass is fully loading the left, center, and right
channels, the LFE channel could increase the bass intensity by up to 6 dB
."



The total redirected bass and LFE from Pulse must add more than 6 dB to the LFE level. High level bass in all channels according to JBL's waterfalls. That means 5 channels of high level bass being added to the LFE channel.

I don't own the movie not do I want to, but playing this thing at reference level requires a powerful subwoofer (SPL and extension)!


Pulse Waterfalls - R, L, C, LS, RS, LFE
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post #93 of 131 Old 08-25-2009, 09:32 AM
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Quote:
Originally Posted by Ed Mullen View Post

The conversion from dB to Pascals is required in order to sum SPL, as m-fine correctly points out. The conversion is (10^(dB/20))*0.00002. 94 dB is 1.00 Pascal, for a quick way to check this.

dB Pascals
115.00 11.246827
105.00 3.556559
105.00 3.556559
105.00 3.556559
105.00 3.556559
105.00 3.556559

Summed Value dB = 123.24

If there was a simultaneous 0 dBFS peak in all 5 speaker channels and in the LFE channel, and if they were all routed through the same transducer (i.e., the subwoofer) in order to avoid phase cancellation issues, they will sum to 123.24 dB.

In order to actually prove this, a friend of mine encoded a Dolby Digital DVD with 30 Hz test tones at -20 dBFS (no dial norm adjustment). One tone for a single speaker channel, and then one tone with all 5 speaker channels and the LFE channel. The SPL increase going from a single channel to all 5 speaker channels + the LFE channel was exactly 18 dB. So there is no funny business going on inside the decoder - it really is a straight-up additive/summation of all the sound pressures.

As bosso states, the chances of this actually occuring on a DVD are almost completely nil and I agree completely. But that doesn't change the math or the outcome of our experiment.

Additionally, the dialnorm of the DVD will affect playback levels. A -31 DN for a consumer decoder means no adjustment of playback level. Most DD DVDs are -27 DN, so the playback level is reduced by 4 dB.

So if the following scenario applied:

-the system was calibrated to Dolby Reference Level at master volume 0.0
-the system was calibrated with a -31 DN value for the source
-there was a simultaneous 0 dBFS peak in all speaker channels and the LFE channel
-the source DVD also had a DN of -31

Then the playback SPL at master volume 0.0 would be ~123 dB. If the source DVD had a -27 DN (which is common), then the playback level would be ~119 dB.

BTW on my calibrated system at master volume 0.0, the -20 dBFS "all channels" tone plays at 103+ dB, so that puts me square at ~123 dB if we had encoded the tones at 0 dBFS.



Great post Ed. In theory 123.24 db can be expected from your sub channel when calibrated and running at reference. I figure rare 118-119db peaks are more likely in reality. Of course a lot of people prefer to run their sub channel 3-6db hot placing even further demands on it, counteracted by the fact that not many people watch their movies that loud.

I came up with the front 3 channels adding about 5.785db theoretically and all 5 channels including surrounds adding about 8.24db to the sub output for a maximum of 123.24db from the sub channel at calibrated reference level, in theory. Close enough to what you came up with for me.
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post #94 of 131 Old 08-25-2009, 10:11 AM
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Quote:
Originally Posted by Ricci View Post

Great post Ed. In theory 123.24 db can be expected from your sub channel when calibrated and running at reference. I figure rare 118-119db peaks are more likely in reality. Of course a lot of people prefer to run their sub channel 3-6db hot placing even further demands on it, counteracted by the fact that not many people watch their movies that loud.

I came up with the front 3 channels adding about 5.785db theoretically and all 5 channels including surrounds adding about 8.24db to the sub output for a maximum of 123.24db from the sub channel at calibrated reference level, in theory. Close enough to what you came up with for me.

Right - I've never seen a DD DVD without at least -27 DN, so we're probably looking at a maximum of ~119 dB in practice at MV 0.0. Again assuming a 0 dBFS peak in all five channels and in the LFE channel, which is very rare, but certainly possible as the Pulse link shows.

We don't know if the Pulse bass peaks actually were encoded at 0 dBFS, as the spectral color charts are all relative. I suppose someone would need to actually engage the mixing engineers for the actual encoding levels for that scene. Maybe they are all at -7 dBFS for all we know.

Correct - three speaker channels at 0 dBFS would add 5.79 dB to the LFE channel.

dB / Pascals
115.00 11.246827
105.00 3.556559
105.00 3.556559
105.00 3.556559

dB Summed Value = 120.79

Maybe my point about phase cancellation was previously overlooked by some, but bosso is cooking with oil now. I can see where he was getting 3 dB gain from two sources, but that does indeed assume random phase. When frequency, phase, and amplitude are all identical, two sources will indeed sum +6 dB.

The upshot is five full-range speaker channels and the LFE channel going to the subwoofer will only equal the SPL of all redirected bass and the LFE channel going to just the subwoofer when the frequency in question is deep enough to avoid a modal response in the room and associated peaks/nulls and phase cancellation.

At frequencies above the pressure/modal transition frequency of the room, we could indeed expect less than perfect/theoretical summing from five discrete speaker channels, as they would not be considered perfectly in phase and there would undoubtedly be some cancellation at work.

The only way to assure perfect summing is to use one transducer for all six channels. With that said, if we push the source frequency deep enough, and get the room well into the pressure mode, the physical distance between the five sources starts to become less significant from a phase standpoint, and the summing should start to approach theoeretical, but would probably never reach it due to lossy boundaries.

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post #95 of 131 Old 08-25-2009, 10:36 AM
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Quote:
Originally Posted by Ed Mullen View Post


Right - I've never seen a DD DVD without at least -27 DN, so we're probably looking at a maximum of ~119 dB in practice at MV 0.0. Again assuming a 0 dBFS peak in all five channels and in the LFE channel, which is very rare, but certainly possible as the Pulse link shows.



Off the top of my head, I know that the following movies use a DN value of -31.

Air Force 1

All the Lethal Weapon movies

The Dark Knight

All the old James Bond movies that were remastered in DD and DTS

Casino Royale



In addition, a lot of THX units base their "Reference Level" calibration to the typical DVD encoded with a DN value of -27. A DD unit uses a calibrated playback volume that is calibrated for the lowest DD DN value of -31.

In other words, a THX unit is calibrated to playback any DD movie 4 dB louder than a DD unit.



Quote:
Originally Posted by Ed Mullen View Post


We don't know if the Pulse bass peaks actually were encoded at 0 dBFS, as the spectral color charts are all relative. I suppose someone would need to actually engage the mixing engineers for the actual encoding levels for that scene. Maybe they are all at -7 dBFS for all we know.


Very true. MKTheater gets some very high SPL levels (AKA over 120 dB) on that particular DVD, so it must be recorded close to that level.

I read somewhere that the only signal that can be recorded at -1 dB FS and can be converted back to analog without overload of the D to A converter is a square wave. A single sine wave require a -4 dB FS level due to the 3 dB crest factor of a sine wave. So, a single sine wave recorded at -4 dB FS will result in an approximate -1 dB FS analog signal coming out of the D to A converter.

I hope I got that right!
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post #96 of 131 Old 08-25-2009, 11:06 AM
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Thanks - didn't realize there were actually a handful of DD releases out there with -31 DN. DTS doesn't use it at all, of course - so the default "equivalent value" would be -31 DN for all DTS tracks, which is why they usually play 4 dB louder than their DD counterparts at the same MV setting.

In-room SPL peaks reported by users must be viewed with a grain of salt - the assumptions must be:

- the in-room FR is perfectly flat to ULFs
- the subwoofer channel calibration level is level/even (not running hot)
- the system is calibrated to exactly Dolby Reference Level at MV 0.0 using a -31 DN source
- the source material itself is -31 DN
- the device recording the SPL peaks is actually accurate (and the RS meter doesn't qualify in my book)

That's a lot of assumptions and qualifiers. All we really know is MKTheater's DIY creations are capable of prodigious SPL without distortion or compression.

As an aside, there are stirrings inside CEA on a recommended calibration level for HT systems which will approximate what we experience (from an SPL standpoint) in commerical movie theaters. And (as one might suspect) it's a bunch under Dolby Reference Level.

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post #97 of 131 Old 08-25-2009, 11:32 AM
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I wonder if Kain has absorbed all this! I know this thread has taught me a few things I did not know or had not thought about. Thanks Ed, Bosso, Cass and others for a lively yet informative discussion.
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post #98 of 131 Old 08-25-2009, 02:01 PM
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Quote:
Originally Posted by Ed Mullen View Post

Thanks - didn't realize there were actually a handful of DD releases out there with -31 DN. DTS doesn't use it at all, of course - so the default "equivalent value" would be -31 DN for all DTS tracks, which is why they usually play 4 dB louder than their DD counterparts at the same MV setting.

No doubt. WOTW and other DTS tracks are notably way hotter overall than other movies with DD tracks. Pulse is quiet by comparison. The bass is crazy relative to the overall track volume, but if you compare it with M&C or WOTW's DTS track at the same volume setting it's night and day.
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post #99 of 131 Old 08-25-2009, 02:09 PM
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Quote:
Originally Posted by Ricci View Post

No doubt. WOTW and other DTS tracks are notably way hotter overall than other movies with DD tracks. Pulse is quiet by comparison. The bass is crazy relative to the overall track volume, but if you compare it with M&C or WOTW's DTS track at the same volume setting it's night and day.

I think the difference between DD/DTS on M&C is around 8 dB. 4 dB because DTS doesn't use DN and the DD version is presumably -27DN. And then 4 dB due to a what I suspect is likely a global difference in the overall encoding level between the two sound tracks. Either that or M&C DD has a -23DN.

Anyway, measure the bass peaks on the cannon battle for the DD/DTS tracks at the same MV setting and my recollection is that they are around 8 dB apart.

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post #100 of 131 Old 08-25-2009, 03:48 PM
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Quote:
Originally Posted by Ed Mullen View Post


As an aside, there are stirrings inside CEA on a recommended calibration level for HT systems which will approximate what we experience (from an SPL standpoint) in commerical movie theaters. And (as one might suspect) it's a bunch under Dolby Reference Level.



Just like this discussion, that will just be an academic exercise. I never playback at full calibrated reference level.

Reason # 1 is it is just too loud.

Reason # 2 is my system can not playback that loud with the current batch of loud action movies being used as a source.

Reason # 3 is which "reference level"? DTS or DD?

My nominal master volume setting is about 6 - 8 dB below calibrated reference level for DVD playback.
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post #101 of 131 Old 08-25-2009, 03:58 PM
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Quote:
Originally Posted by Ed Mullen View Post

I think the difference between DD/DTS on M&C is around 8 dB. 4 dB because DTS doesn't use DN and the DD version is presumably -27DN. And then 4 dB due to a what I suspect is likely a global difference in the overall encoding level between the two sound tracks. Either that or M&C DD has a -23DN.

Anyway, measure the bass peaks on the cannon battle for the DD/DTS tracks at the same MV setting and my recollection is that they are around 8 dB apart.




The Master & Commander DVD DD version uses a DN value of -27. In my system, the DTS version plays back 4 dB louder.

You may be thinking of the War of the Worlds DVD. The WOTW DD version uses a DN value of -23. In my system, the DTS version plays back 8 dB louder.

The only reason that I know the DD DN values of these movies is because my receiver has a Dialnorm value readout on my on receiver's master display.
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post #102 of 131 Old 08-25-2009, 04:03 PM
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Quote:
Originally Posted by J_Palmer_Cass View Post

The only reason that I know the DD DN values of these movies is because my receiver has a Dialnorm value readout on my on receiver's master display.

ok, i was just about to ask what the hell "DN" was

http://en.wikipedia.org/wiki/Dialnorm

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post #103 of 131 Old 08-25-2009, 04:50 PM
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Quote:
Originally Posted by Ed Mullen View Post

As an aside, there are stirrings inside CEA on a recommended calibration level for HT systems which will approximate what we experience (from an SPL standpoint) in commerical movie theaters. And (as one might suspect) it's a bunch under Dolby Reference Level.

Quote:
Originally Posted by J_Palmer_Cass View Post

Just like this discussion, that will just be an academic exercise. I never playback at full calibrated reference level.

Reason # 1 is it is just too loud.

Reason # 2 is my system can not playback that loud with the current batch of loud action movies being used as a source.

Reason # 3 is which "reference level"? DTS or DD?

My nominal master volume setting is about 6 - 8 dB below calibrated reference level for DVD playback.

I think that was the point, no? What you normally experience in the theater is "a bunch under Dolby Reference Level".

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post #104 of 131 Old 08-25-2009, 06:04 PM
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Quote:
Originally Posted by otk View Post

ok, i was just about to ask what the hell "DN" was

http://en.wikipedia.org/wiki/Dialnorm

I found this the other day...

http://www.hometheaterhifi.com/volum...on-6-2000.html

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post #105 of 131 Old 08-25-2009, 06:58 PM
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Hey guys. The theaters I have been too recently did have some loud bass and at reference levels(THX theaters). I consider them the good ones. It's all subjective. I just watched shooter at reference levels and it was very good, not too loud at all(loud but not harsh). I had a range of people from 17 year old girls and 63 year old men and none of them said it was too loud. They are family and would tell me the truth as I always ask just to be curtious.

If you think I am nuts get this. I have always thought my reference level was -10 MV and I ran the subs hot at 10db's. My clipping lights would come on at times(very breifly) and thought I did not have enough power for my subs. Then I realized that I was hitting 135 db's or more. Since then I turn the subs down 10 db's to flat and MV down 5 db's. That gives me 120-123 db's max peak. It still sound awesome at those elevated levels and not harsh. Those extreme peaks are bass only and the highs did peak at 110 db's but now 105 db's.
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post #106 of 131 Old 08-25-2009, 07:24 PM
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Does Dolby TrueHD use DialNorm at all?

Lombardi said it:
Perfection is not attainable, but if we chase perfection we can catch excellence."

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post #107 of 131 Old 08-26-2009, 06:41 AM
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Quote:
Originally Posted by craig john View Post

Does Dolby TrueHD use DialNorm at all?


Good question. After a little research, it appears that Dialnorm is used. DRC is also available.


http://www.dolby.com/uploadedFiles/z...0925_Final.pdf



"20. What is metadata?

Metadata is control information that
accompanies the audio data in a Dolby
TrueHD stream, allowing a content producer
to define a consistent playback experience
for consumers, whether they are listening on
a two-channel stereo system, a 5.1-channel
system, or a high-end, discrete 7.1-channel
home theater system.


21. Does Dolby TrueHD feature any metadata
applications? What are they? How will they
benefit the consumer?

Dolby TrueHD is designed to offer
comprehensive metadata functionality similar
to that found in Dolby Digital and Dolby Digital
Plus. This includes downmixes that are defined
by the content producer, dynamic range
compression for late-night listening, and
dialogue normalization to ensure consistent
playback loudness between different content.
For future content featuring discrete 7.1-channel
playback, Dolby TrueHD also supports multiple
7.1 configurations, enabling the full creative
possibilities of next-generation sound design
to be delivered to the consumer environment."
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post #108 of 131 Old 08-26-2009, 06:47 AM
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Quote:
Originally Posted by sivadselim View Post

I think that was the point, no? What you normally experience in the theater is "a bunch under Dolby Reference Level".


This is an interesting issue. I am not so sure that movie theaters measure lower SPL levels than the calibrated Dolby (or THX or DTS or SDDS) Reference Level.

From what I have heard, large rooms like a mixing stage or a movie theater do not sound as loud as a small room given the same playback volume level.

The reasons given are:

1. Reverberation differences between a large and small room.

2. Bass management is not used except in home systems.
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post #109 of 131 Old 08-26-2009, 06:52 AM
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Quote:
Originally Posted by MKtheater View Post

Hey guys. The theaters I have been too recently did have some loud bass and at reference levels(THX theaters). I consider them the good ones. It's all subjective. I just watched shooter at reference levels and it was very good, not too loud at all(loud but not harsh). I had a range of people from 17 year old girls and 63 year old men and none of them said it was too loud. They are family and would tell me the truth as I always ask just to be curtious.

If you think I am nuts get this. I have always thought my reference level was -10 MV and I ran the subs hot at 10db's. My clipping lights would come on at times(very breifly) and thought I did not have enough power for my subs. Then I realized that I was hitting 135 db's or more. Since then I turn the subs down 10 db's to flat and MV down 5 db's. That gives me 120-123 db's max peak. It still sound awesome at those elevated levels and not harsh. Those extreme peaks are bass only and the highs did peak at 110 db's but now 105 db's.


135 dB?

Yikes! Thank goodness you recalibrated.


Shooter at reference level?

Perhaps a Yikes is in order, but maybe not!
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post #110 of 131 Old 08-26-2009, 07:07 AM
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Quote:
Originally Posted by bossobass View Post


Contrary to popular belief, the levels encoded are watched extremely closely by the top people in the field.

Tom Holman:


Quote:

I have done hundreds of DVD feature remastering with a THX rep watching my meters!!! I can tell you their limit is max peaks at -6dBFS, momentary peaks during explosions etc not to exceed -4.



Sorry for the long reply. Just throwing out some trivia from my vaults.

Bosso



I played around with this a bit, and a single sine wave will just start to clip at the -3 dB FS level. The THX -4 dB FS level limit for momentary peaks will give you full non-clipped reference level analog output voltage out of the D to A converter.

Normal MAX peaks of - 6 dB FS seems to be an excellent idea, but that is only 2 dB down from maximum analog output levels nased on what I have measured.
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post #111 of 131 Old 08-26-2009, 08:49 AM
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Quote:
Originally Posted by J_Palmer_Cass View Post

This is an interesting issue. I am not so sure that movie theaters measure lower SPL levels than the calibrated Dolby (or THX or DTS or SDDS) Reference Level.

From what I have heard, large rooms like a mixing stage or a movie theater do not sound as loud as a small room given the same playback volume level.

The reasons given are:

1. Reverberation differences between a large and small room.

2. Bass management is not used except in home systems.


I just watched Inglorius Basterds at a local theater and it was pretty durn loud (didn't sound that great though). I don't know how loud it was but peaks and dialog seemed louder than I normally watch movies at home which is -15 to -10 depending on the movie. It could've been close to REF, but that'd be a guess.

How do they set the volume levels for a large theater? Do they go for the center of the venue, or is there a predetermined seat position that they use? Maybe it's an average over many seats? Hopefully.
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post #112 of 131 Old 08-26-2009, 08:59 AM
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I've read that sometimes it's by the amount of people in the theater.
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post #113 of 131 Old 08-26-2009, 12:44 PM
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They still have movie theaters?
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post #114 of 131 Old 08-26-2009, 01:36 PM
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Quote:
Originally Posted by J_Palmer_Cass View Post

This is an interesting issue. I am not so sure that movie theaters measure lower SPL levels than the calibrated Dolby (or THX or DTS or SDDS) Reference Level.

From what I have heard, large rooms like a mixing stage or a movie theater do not sound as loud as a small room given the same playback volume level.

The reasons given are:

1. Reverberation differences between a large and small room.

2. Bass management is not used except in home systems.

I think there is probably some "aural illusion" going on as well. In my little den, well below reference, my system seems ferocious compared to anything I have heard in any of the local theaters (except for maybe the fake(?) IMAX that I am really impressed with). But I would have to see the actual measurements before I would come to any conclusion. That objective comparison is FAR from a DBT.

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
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post #115 of 131 Old 08-26-2009, 03:06 PM
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Originally Posted by m-fine416 View Post

They still have movie theaters?

Sure. It's just hard to find a good, wise-cracking robot to go with you.

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post #116 of 131 Old 08-28-2009, 06:58 PM
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Originally Posted by J_Palmer_Cass View Post

This is an interesting issue. I am not so sure that movie theaters measure lower SPL levels than the calibrated Dolby (or THX or DTS or SDDS) Reference Level.

From what I have heard, large rooms like a mixing stage or a movie theater do not sound as loud as a small room given the same playback volume level.

The reasons given are:

1. Reverberation differences between a large and small room.

2. Bass management is not used except in home systems.

I thought "reference level" was referring to what you would hear in a movie theatre calibrated to that reference, and so it should be the same volume in your home theatre. Mind you, I don't recall any movie theatre that I've been to that sounded as loud in the theatre as what I get at home at calibrated reference level so I'm not sure. People have said that the larger venue gives the "illusion" that it's not as loud.

I dunno, all I know is that reference level is for impressing your pals with demos but not for watching whole movies.

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post #117 of 131 Old 08-29-2009, 08:20 AM
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I watch all my movies at reference levels.
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post #118 of 131 Old 08-29-2009, 08:34 AM
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Originally Posted by MKtheater View Post

I watch all my movies at reference levels.

I watch all my movies at +10 over reference level.
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post #119 of 131 Old 08-29-2009, 08:58 AM
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Originally Posted by plusminus3db View Post

I watch all my movies at +10 over reference level.

I tried to watch all my movies at +100 db over ref, but the tweeters fell out of the speakers and the amps caught on fire. Now I stick to +20.
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post #120 of 131 Old 08-29-2009, 09:20 AM
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