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SMPTE standards now void

4K views 38 replies 13 participants last post by  GXMnow 
#1 ·
I was able to visit the Audio Engineers Society conference at the LA Convention Center last weekend.

One of the presentations I attended was in the Sound for Pictures group - a presentation on a new SMPTE report on cinema audio standards.

I've since downloaded the report (it's about 200 pages, but free download from the SMPTE and AES). I'm now reevaluating how my HT systems are calibrated, because its clear that no one is following the existing standards and the X-curve at the studios.

This is a major report. The graphs show how bogus the whole standards compliance is. I was stunned to see that the studio mixing rooms are up to 20dB different at some frequencies!

As I understand, the current SMPTE standards rely on pink noise and real time analysis - which is known to be wrong in big rooms. And the theaters that have been "chasing" the x-curve with massive EQ are now seen to be a big problem for exhibition.

Following on from this report, I removed all the EQ from my main system, and it was immediately apparent that there is more definition and detail without all the EQ. As the THX concept is based on these standards it would seem THX is a dead letter too (it already is at the theater level).

It would seem that this is going to be the definitive word on the subject, with much of the committee producing the report from Dolby and other major audio companies. Even Ian Allen who's work started the modern era in cinema sound has ratified the report.

I urge anyone with an interest in HT to download and read the report - I'd like to discuss it further with those more technically astute, as much of it is over my head, technically speaking.
 
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#2 ·
The SMPTE calibration thing (pink noise @ 85 dBC) is to insure that playback level in the theater is the same as where the content is being created. They never claimed that you would enjoy listening to "calibrated" playback levels! That was demonstrated in one of the 137th workshop sessions - basically theaters have been turning playback levels down in response to listener complaints of excess loudness.

The X-curve derives from the original "Academy" curve, as proposed by Dolby Labs. Eventually was standardized by SMPTE for theater reproduction. Neither were intended for home use.

My experience with a variety of source material is that they are all over the map in terms of spectral balance. Some content sounds fine when reproduced flat, while other content sounds noticeably (excruciatingly) bright and requires some sort of EQ. Unfortunately, there is no one-size-fits-all in terms of EQ settings. What works for one movie or TV show may not work for another. Some require dynamic EQ while others work with static EQ settings, and in extreme cases, I have to use both.
 
#3 ·
The SMPTE calibration thing (pink noise @ 85 dBC) is to insure that playback level in the theater is the same as where the content is being created. They never claimed that you would enjoy listening to "calibrated" playback levels!
+1. Calibration standards only exist to give theater owners a starting point. It doesn't account for the taste, or lack of same, of the director with respect to the audio mix. That especially applies to bass content, where the director may or may not pander to the wishes of soon-to-be-deaf male adolescents. :rolleyes:
 
#4 ·
Data on this front has been out for a couple of years in various reports and work to fix things. See this post I wrote earlier: http://www.avsforum.com/forum/91-au...3482-how-cure-square-room-2.html#post27459930

===============

Audyssey doesn't use the "wrong target curve." :rolleyes:

It uses a "flat" target curve... but it ONLY does so at FULL Reference Level. IOW, when you listen to the content at the exact same volume it was recorded at, it is reproduced at the exact same level, with the exact same FR, it was recorded at. If I was a recording engineer, this is exactly what I would want in a sound reproduction system... EXACT fidelity to levels and FR to the original!
What you describe is a laudable goal, i.e. hearing the “original” sound that the talent/engineers heard when they created that soundtrack. We all want that. Alas this is more of a dream/aspiration than something we can remotely achieve. Audio distribution is “broken” that way. There simply is not enough data in the system to help replicate that experience.

For us to match what was heard, both our system and theirs need to comply with the same exact standard. While such a means exists for video, it does not for audio. Your point therefore that by setting the target response to “flat” (at full SPL) will get us there, is not correct. Doing so in your system does not produce the same frequency response as was heard in the dubbing/mixing theater. Or even closely approximate it. Believe it or not most of the problem is on the production side!

This is a well-known problem in the industry and one that is being addressed. To wit, let’s look at the AES paper, " A New Draught[draft] Proposal for the Calibration of Sound in Cinema Rooms (21/4/12)" by Newell and Holland. In there, they show measurements of 11 Dolby certified Mixing Rooms ("dubbing theaters") and real theaters both of which are calibrated according to X-curve (so called standard):


Notice that these “certified” cost-no-object rooms are not remotely matching each other. The authors of the paper points out the very point on how broken the industry practices are:

"Figure 1 shows a set of response curves from the calibration positions of 20 different rooms, most of which are considered to sound noticeably different from each other."

Clearly if the production side of one movie doesn’t match that of another mixed in a different room, then us using a single target response will in no way assure us to hear the same sound at any of these spaces.

There is lots more data like this. Here is a survey Genelec did on their installations in such spaces:

A Survey Study Of In-Situ Stereo And Multi-Channel Monitoring Conditions
Aki V. Mäkivirta and Christophe Anet
Genelec OY
Olvitie 5, Iisalmi, Finland




Once more there are large variations from that flat response as shown in the previous study.

The reason the situation is so screwed up on the production side is that it is an old system based on hardware capabilities that date back literally decades (the so called "X-curve" in red above). It also ignores what we have learned about psychoacoustics of frequency response variations in rooms. Trying to copy that target in our room equalization is therefore going back in time and progress we have made in doing better, much better.

So what should we do here? The logical path would be to set the target curve to what we like! Seems simple enough but we refuse to go there because of the argument of deviating from the production side being a "bad" thing. Now that we know we are always deviating and such matching is not possible, then the best thing to do is optimize for sound that we like. After all, isn’t that the ultimate goal? Getting the most enjoyment from the soundtrack?

Now you could go and spend months and years experimenting trying to figure out what you like. Alternatively you can do as I suggested. That is stand on the shoulders of industry giants who have done such tests and created the likely response curve we are going to like. This is one of a number of examples from Sean Olive et al. AES paper:

The more preferred room corrections (RC1-RC3)
produced smoother curves with more extended output
below 60 Hz. The slope of the curve also seems to be an
important indicator of preference: The more preferred
room corrections had more downward sloped curves,
whereas the least preferred room corrections (RC5 and
RC6,) tended to have flatter slopes, probably related to
the manufacturer’s choice of target curve.


So unless you have your own data that says we prefer something else, the overwhelming evidence points to a sloping down curve being the right target, not some attempt at matching a standard which never existed in the first place and is more broken than anything we can do in our homes.

Audyssey has developed at system to compensate for those human hearing sensitivities, known as Dynamic EQ. When you listen at volume levels below the levels the content was recorded at, Audyssey's Dynamic EQ, adds a boost to the low frequencies that imparts Audyssey's version of a "Fletcher Munson" curve:
Dynamic EQ in general is an orthogonal feature to this discussion. Indeed it could do its thing just the same whether you used room equalization or not. So it has no relevance in this discussion as to what the correct target curve should be. As always you want to start with the correct way to configure the system and then adjust from there. Not set it wrong and hope that some other manipulation happens to automatically cure the issues of the first.

==============

Unfortunately people tend to ignore all of this and continue to believe in some mythical "standard" to which they are calibrating their systems. Here is my saying the same thing some 15 months back: http://www.avsforum.com/forum/91-au...ues-how-interpret-graphs-82.html#post23177669. And post the same earlier.
 
#19 ·
So unless you have your own data that says we prefer something else, the overwhelming evidence points to a sloping down curve being the right target, not some attempt at matching a standard which never existed in the first place and is more broken than anything we can do in our homes.
I believe there *IS* data that has subjectively identified "what listeners want to hear". Floyd Toole was doing such work at Harman, and I believe his successor Shawn Olive has expanded on this work - including identifying what listeners want to hear on headphones.

And both are close to flat, and look nothing like the "x-curve".
 
#5 ·
A link would have been nice.
 
#8 ·
There are several aes papers on the subject x-curve and cinema sound, I have briefly looked into some of them.

What seems to be the case about the x-curve is that it was originally an attempt to make a method for easy equalization of theater sound systems so that they achieved a flat direct-sound frequency response from the speakers, using pink noise.
The x-curve was then supposed to reflect the frequency-dependent increase in room-gain due to reverb and reflections.
While at it, they found the sound to be better if a small roll-off in the bass was added as well, due to speaker system limitations.
The x-curve does not follow a linear tilt, such as the one proposed by Bruel&Kjaer (a linear 3dB/decade tilt).
An eas report (from 2011) shows that the x-curve fail to match the frequency response of typical theaters.

Until someone orders a theater speaker system I really do not care what they do in cinemas, but it is very interesting to know what kind of calibration they actually use in the dub-stages/studios.
This response is what the producers hear and use as reference when they make the soundtrack, and if my system is not calibrated similar to this, the sound will not be like it was intended.

It is obvious that there are huge variations in sound from soundtracks, both in dynamic contrast, frequency balance, some are distorted due to heavy clipping, some are filtered so that all the low bass is lost.
Some differences are artistic, and welcome, we like the variation, and different movie genres benefit from different sound.
But some of the differences may sound like it could be caused by differences in monitoring speaker systems.

I have not read the 200+ pages report, I will look into it, and report back if I feel I can contribute in any way, or just for the discussion.
 
#9 ·
Just to clarify what I am trying to say here;

...
An eas report (from 2011) shows that the x-curve fail to match the frequency response of typical theaters.
...
Here the term "frequency response of typical theaters" means the changes from flat caused by room acoustics.

.. but it is very interesting to know what kind of calibration they actually use in the dub-stages/studios.
This response is what the producers hear and use as reference when they make the soundtrack, and if my system is not calibrated similar to this, the sound will not be like it was intended.
...
Badly written.
I do not mean that the calibration reference response should match, it is the whole chain that must match, and that includes de-emphasis of the x-curve that one must assume is done on all content intended for home theater use.

A theater must follow the same standards used at the dub stages, x-curve - playback will then be the same as production.
Home theater must be calibrated flat - playback will the be the same as production for content corrected for x-curve.
 
#10 ·
Having looked at the report, I find the situation to be better than expected.

All venues follow the x-curve calibration, and deviation is far less than that shown for studios in the Genelec report.
If content intended for home is corrected for x-curve to flat, this should play as intended on a home theater system calibrated to flat response.

General performance of the systems investigated are easily exceeded in a properly designed home theater.
Especially the low frequency reproduction is lacking, there is little control of room acoustics at low frequencies, and subwoofer systems are not properly set up.

If there is any interest in further discussion, I would like to see what others think, and the report rises some very interesting questions about sound reproduction and calibration.
 
#18 ·
Having looked at the report, I find the situation to be better than expected.

All venues follow the x-curve calibration, and deviation is far less than that shown for studios in the Genelec report.
You're kidding, right? You've got dubbing rooms with a 10dB swing in midrange (voice) frequency bands, and greater than that at 8kHz. I would have expected Hollywood to be "better than the Genelec report", because this is the HEART of film production in the world. Likewise for the theaters - this is LA, not Omaha. This is a disastrous report for the SMPTE and the film business, and for Dolby as well. Dolby has been the so-called "enforcer" of the standards, and clearly they didn't do it. If you read the report thoroughly, it's clear why no one is meeting the standard - they're EQ'ing using pink noise and real time analysis (RTA). The music business used RTA for recording studios for about 2 years, and then discarded it. Hollywood kept using it. And it's a bogus measurement in a small mix room, and even more absurd in a large room.


If content intended for home is corrected for x-curve to flat, this should play as intended on a home theater system calibrated to flat response.
Wrong.

If there is any interest in further discussion, I would like to see what others think, and the report rises some very interesting questions about sound reproduction and calibration.
It's a great report.
 

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#11 ·
Afaik, mostly from reading filmmixer's posts, until recently no corrections from the x curve were made for home media. Iow older discs contain exactly the theatrical mix. Since remastering has become common, there are zero rules for the remastering process so whether the x curve is explicitly decompensated is an unknown that can vary from disc to disc depending on the remastering engineer, and maybe for the same engineer across time. No rules equals perfect uncertainty.
 
#12 ·
Would be interesting to have some input on this from someone in the industry.

What I found was that some older DVDs do not have de-emphasis, i.e. they will sound too bright, while all later films on BD is corrected.

Also, it would be interesting to know the exact correction curve, as it may not be an exact inverse of the x-curve used for calibration.

It is also curious to note that while audiophiles loose their sleep over deviations that are questionable as audible at all, we can not say for sure whether the movie is actually 10dB hot in the treble..
 
#13 ·
The above commentary suggests that there is an assumption that the only content being viewed (and listeneed to) at home is from movie soundtracks mixed in a large theater setting to the x-curve.

Not in my home! I playback content derived from old movies that were mixed originally to one of the Academy curves, content derived from old TV shows that were mixed to who knows what standard, content derived from what you might refer to as "cable TV channels" which certainly are not being mixed in a large theater setting to the x-curve, content from YouTube, and Bluray content from the x-curve movie theater setting.

Imposing a blanket playback response characteristic (like a modified x-curve) doesn't work, because there is such a wide variability between the different sources. If you want optimum listening pleasure and results, you need to learn how to use and apply EQ when it is warranted. Otherwise, you have to tolerate the quirks and deficiencies in the disparate source material.
 
#15 ·
...
If you want optimum listening pleasure and results, you need to learn how to use and apply EQ when it is warranted. Otherwise, you have to tolerate the quirks and deficiencies in the disparate source material.

That is one way to do it - individual eq for everything, applied as you find suitable.
Not very common, I think, most calibrate their system to something closer to flat, and leaves it like that, for all content.

But for movies made in dub-stages calibrated to the x-curve, it is possible to predict the response used for monitoring, because the report shows that the dub stages are calibrated according to the x-curve.

This material is then intended for theaters, which are also calibrated according to the same.

The question is then, if the soundtrack distributed for home is corrected in some way, and what correction curve is used.
An exact inverse of the x-curve would not necessarily be correct.

If it is not corrected (Encoded for x-curve playback), the actual response will sound too dull in the upper midrange and too bright in the upper treble, if the playback system is calibrated for flat on-axis in a small room.
 
#37 · (Edited)
#27 ·
If Filmmixer reads this thread, perhaps you could come up with some information on the issue of de-emphasis.
I remember recently checking out the list of work you have been involved in, it is quite extensive.
If you (Filmmixer) don't know, it may be fair to assume that there are no established practice for this?

Not wanting to jump in to conclusions here, but from reading the report, and from what others in this thread says, it is clear that both the theaters and the dub-stages where they make the soundtracks are far from state-of-the-art performance in sound reproduction.

I find it surprising that some issues apparently could be solved quite easily.
The screens most commonly in use have an attenuation in the range 6 to 10 dB at high frequencies, causing the hf drivers to overload in an attempt to overcome this.
The screen used in dub-stage F is of a different kind, with far better acoustic transparency, and it is mentioned in the report that the sound quality was noticeably better, and since the speakers were the same as in a different dub-stage, they suspect that the screen is to be blamed.
A screen that is not sufficiently transparent will cause attentuation and reflections, which will have a negative impact in sound quality.
This could be fixed right away, they could swap out the screen and recalibrate, and gain 6-10dB headroom and better clarity due to less reflections.
 
#28 ·
The question is then, if the soundtrack distributed for home is corrected in some way, and what correction curve is used.
An exact inverse of the x-curve would not necessarily be correct.

If it is not corrected (Encoded for x-curve playback), the actual response will sound too dull in the upper midrange and too bright in the upper treble, if the playback system is calibrated for flat on-axis in a small room.
The purpose of x-curve is to make reproduced sound appear flat at high frequencies in a B-chain theater environment. The curve (3 dB/octave rolloff above 2 kHz) was derived by adjusting the frequency response of behind-the-screen speakers in a full sized movie theater environment to match the sound of near field KEF loudspeakers, positioned directly behind the mixing console. The nearfield reference loudspeakers were not rolled off (i.e. were flat).

In a home listening or playback environment, which is usually non-reverberant, you don't use any x-curve rolloff at all. You just play the soundtrack back flat. According to x-curve theory and legend, what they hear in the theater with the x-curve compensation is supposed to jive with what you would hear at home with your near field speakers playing back flat. Whether or not that actually works in practice, certainly can be debated.

As I noted in my original commentary above, I have several Bluray discs of feature film content in my collection made within the last decade or so, and when I play the soundtracks back flat through my (ruler flat) KH monitor speakers, the sound quality is just peachy. No sizzing or dripping, and no EQ is needed to enjoy the performance. So, it can be done. I'm assuming that these soundtracks were mixed in a typical x-curve theater environment.

What you DON'T want to do is apply the x-curve where it doesn't belong, because all you are doing is rolling off the top end. If you have bad sounding soundtrack audio, the only way I've found to fix the problem is to apply the appropriate type of EQ correction, which typically doesn't look at all like an x-curve. In other words, applying x-curve to your home playback system in the hopes that it's going to automatically correct or compensate for bad sounding audio is FALSE.

SMPTE monitor calibration and frequency response alignment belongs in a movie theater B-chain environment - not in the home.
 
#29 ·
This is nothing new:

Read Chapter 3:

http://www.hps4000.com/pages/special/missing.pdf

a quote:

"The situation became so bad the theatre purchased a second set of equalization modules
for everyone else to use. The equalizers I set, the so-called house cards, are sealed and
should be left alone. For ten years now, technicians have had their own equalizer modules
with which they may do what they will. As soon as they leave, it is understood that the
house cards will be reinstalled. If ever proof is required that the measurements these well
meaning technicians are making are inaccurate and unrepeatable, consider this: In ten
years, no technician has ever set the second set of equalizers the same way twice. For ten
years, no technician has been able to achieve a sound quality as good as, let alone better
than, that which is available by simply using the house cards as is."

Most of his papers have a decided slant to his products, but I found a lot of good information in there. Another good paper is "The mythical X-Curve" also found on his site.

JSS
 
#32 ·
There is certainly a lot of mis information and just plain bad guessing when it comes to the X-Curve for cinema.

Virtually every room used to dub films are very carefully setup to be very close to the true SMPTE X-Curve.

The process used to achieve it does vary, but in most cases, the systems for the screen channels are Bi, Tri, or even Quad amped with sophisticated speaker management systems to correct the individual drivers first, and time align them to get the best possible response with the least amount of Eq to achieve the result. Using continuous pink noise as the test signal is still the most common practice. Many other systems have been tried and there is some merit to transfer function and sweep setups, but the jury is still out on if the results are as consistent. The response measurement for pink noise is done with a spectrum analyzer and multiple microphones. Most systems still time multiplexed the mic's into the analyzer and a long average is used. 4 or more mic's does a very good job of cancelling out peaks and dips caused by room reflections. The system will fall apart if the room reverb is unusual or excessive. There is no easy electronic fix for bad acoustics. Thankfully, most dubbing rooms have very good to excellent acoustics and this measurement system works very well with consistent results. Newer analyzer software and hardware is allowing up to 8 mic's to be analyzed simultaneously and averaged in real time. Not only does this give a much faster true average reading, the results seem to be more accurate because the time of the readings are in sync.

On a dub stage, the tuning setup is a little different than for a large theatre. First off, there is actually a series of X-Curves that vary the high end roll off based on the room volume to reduce the effect on the perceived sound when the mix is later brought into the larger room. Also, in a large theatre, the mic's are spread over a fairly large area to try and average as much of the prime listening area as possible. Before any Eq is applied, all of the mic's are checked to be sure the response is consistent and that no one mic is in an especially poor seat. Checking the mic's in the off axis areas can also show if speakers need to be aimed better. It is very common to use the fall off of the speakers dispersion pattern to help even out the room coverage from the near and far seats. The closer you get to the speaker, the further you go off axis. This can greatly reduce the level difference from the front to back in a large theatre. On a bud stage, the speakers are pretty well aimed directly at the mix console position. The analyzer mic's are usually placed across the console operator positions. The sound out of that area is not as important as what the director and mixer are hearing. The SMPTE spec calls for +/- 3 db from the X-Curve, but we usually achieve much better. In a well equipped and acoustically correct large room, the average is usually even better than +/- 2 db and some can get under +/- 1 db without excessive Eq. On a dub stage, the average of the 4-6 mic's across the console will first be dialed into better than +/- 2 db, usually 1 db, but then we also look at each mic independantly to make sure no one person at the mix console has an error of more than 2 db anywhere. Having the average stray off perfect is better than the director having a 4 db dip in the dialog range.

The high end roll off has been a target of a lot of debate. Many are arguing that it kills the possibility of ever getting true high fidelity as it limits the headroom of the high frequency range with so much roll off. This simply is not the case in the real world. Let's assume a room was tuned to perfectly flat out to 16 Khz and calibrated to 85 db at -20 dbfs. A sine wave at 16 Khz could then hit 105 db at track clipping. This is just utterly not needed. In a smaller room, the response should hold the 3 db per octave roll above 2 Khz. In this case, the level at 16 Khz will hit PCM 0 DBFS clip at 96 db. That is still a sound I never want to hear. Then there is the reality of even being able to punch that much sound into a large room. Very few speakers could handle it for any length of time. There was a track on a feature I will not name, that had a sound effect that did hit close to 0 DBFS at 15 Khz for about 1 second. There were blown HF drivers all over the country. And this was with the roll off of the X-Curve. Without the X-Curve, that signal would have been Eq'd out 10 db louder still. How did that signal make it out?? Probably 2 things happened. Maybe the dub stage was not Eq'd to hold X-Curve all the way to 15 Khz, and maybe the sound engineer's hearing was a little deficient at that frequency. Maybe the director was asking for this short HF burst to have extreme impact. In any case, the system on the dub stage was able to handle it without failing. so it did not send up a red flag of disaster. And there is also a good chance, the system ran into a limiter, probably in the power amp for the tweeter. This could have cause the sound to just seem too low, making the mix engineer turn it up even hotter. The Myth that the X-Curve is killing too much high end is just not based in the real world.

Any good dub stage is calibrated accurately, and the talent creating the soundtrack is laying down the sound while listening to it on this X-Curve, compensated a bit for room size. The tolerance for the X-Curve does allow more roll off at both the high and low frequency limits, but if the speakers are capable, the roll off does not need to be Eq'd to drop off faster. The normal practice is to just stop boosting when the drivers start to roll off. Pushing drivers past their designed frequency limits is always a bad idea. All of the better systems we work with usually have either a few bands of parametric Eq for each driver, driver correction FIR filter, or Dolby LAKE filter bank correction. These can all apply very smooth correction to flatten each driver. The overall graphic Eq that is used before the crossovers on most systems are limited to no more than +/- 6 db of Eq in each 1/3 octave band. If there is a large swing between bands or if more than 4 db is needed, we usually look to see what is wrong. Eq is used to shape the response, not whole sail change it.

I have tuned many small rooms, some quite a bit smaller than any dub stage, and i still use the small room X-Curve. The result is almost always very pleasing on a wide variety of program material. CD's, SACD, DVD and Blu Ray, and even broadcast TV. If a room is especially small and acoustically dead, we will use a little less roll off. In one room I tuned recently I used only a 2 db per octave roll off that started at 3.15K instead of the normal 2K. The room was actually too dead and needed some life dialed in, but it still actually fell within +/- 3-4 db of true X-Curve and sounded great. Pro Logic II music mode added enough natural sounding reverb to make up for the totally lifeless room.

A good sound engineer does need to adjust for the conditions. We have not found an analyzer system yet that can correct for odd rooms. Systems that use ticks or fast sweeps and ignore the room reverb can have excellent results, but the effect of the room will still effect what the listener hears and the results just do not seem as consistent yet.

Any feature film with a reasonable budget is being mixed in a room that is properly tuned to the X-Curve with fairly tight tolerances and is usually brought to a few larger theatres to make sure it translates well. The bigger studios actually have dub stages that are close in size to the average 300 seat theatre to get a better feel for the final result. I know at least one case where the mixer even sat up on a ladder to simulate being in high stadium seating where the back wall surround would be much closer.

When "near field" home video mixes are made, I am sorry, all bets are off. When testing the final setup in a room I tuned recently, we ran several cinema DCP packages and the client was incredubly happy with the results, but when we switched to the consumer source and played a few Blu Ray disks, the sound was all over the map. There was well over a 15 db difference in the dialog levels between the disks. It was clearly obvious that the theatrical mix was not used on at least 2 of them. The frequency response was a little different, but that was not the big problem here. This person wanted to be able to listen at "reference level" which worked perfectly for the cinema DCP's, but there was no constant refernce we could set for the Blu Ray disks. Turning on the dynamic range control in the Denon Pre Pro actually made it a little worse as the Dolby True HD disks and the DTS MA disks behaved very differently to the level normalization. In both cases, they did reduce the difference in the level from the loud and soft passages, but one raised the quiet sections more and the other lowered the loud sections more. Even with DRC on, we had to play 2 of the disks a full 10 db different in level on the Denon pre pro to have the dialog levels match.

In the end, SMPTE has been looking into any better way to tune rooms for more consistency etc. and they did discuss tuning flat vs X-Curve and other curves. In the real world, X-Curve is working very well. Tuning using FIR or filter banks, with sweeps or even music with a transfer function analyzer can all work, and is being used, but they all are still targeting the X-Curve.
 
#33 ·
There is...
Thank you for this informative post.

Which corresponds very well with my understanding of the conclusions given in the report; calibration according to x-curve is in use.

Some have criticized the level of accuracy of those calibrations investigated in the report, stating that there are significant deviations.
As I tried to explain earlier, when you measure in a room there will always be some dips and peaks, and all of those simply will not disappear, and even if you manage to eq perfectly flat, you just have to move the mic a few inches, and there you are back at where you started.
Some of the larger deviations in lower range of the frequency response are caused by speaker-room interactions, and those can be fixed, but that requires spending some money and the skills to know how to do it.

Whether the x-curve is "wrong" I feel is perhaps not that important, seeing as it is documented and it is then possible to replicate.
And most important - all films are monitored in a similar way, so that when I set up my system so that one movie sounds good, it is likely that other movies will also sound good.

Your comments on near-field are interesting.
I have seen different approaches for calibration of those monitoring systems, they do not seem to follow any specified standard, and you comments confirms this.

I also suspect some of the irreversible destruction of soundtracks happens in this nearfield re-mix situation.
Too many soundtracks come out with distorted and actually clipped audio, with very noticeable distortion from limiters, and heavy compression.
Unlike differences in tonal balance, which is easy and completely reversible to fix, those distortion and dynamic losses can never be undone.

I would rather have the theatrical mix, then at least I know what I have.
And I also have the full dynamic range as originally intended, the dialog is not overly loud, so that it sounds good when played at reference.
 
#38 ·
I work in both the professional world and the consumer world. My experience is very similar to GMXnow's.

I find that some of the most expensive and best sounding speakers in a small room environment with good acoustics will match a variant of SMTPE 222M at the prime listening position with zero EQ using quality microphones and electronics. I find this level of agreement comforting with regard to using the X-Curve as a starting point. I find systems that do not roll off the high frequencies to some extent will sound very irritating at high sound levels with most music and movie sources.

I agree and disagree with Brian McCarty's views in the Home Theater Geeks interview. I believe he is too negative in his views when it comes to the various X-Curve options and equalization. Just because theaters are not very good at hitting the curve does not mean it has no value. Saying RTA's are bad science is far too negative. I use FFT's and RTA's and I find both are useful. I agree with him that equalization is used far too aggressively in many cases and can easily degrade the sound quality, but the sound will not always be better with it off. I do A/B comparisons with clients regularly with the EQ off and on and they prefer on when it is done properly. I also agree that EQ will not solve a bad room. Room acoustics are a different problem than timbre. I find EQ is best used to correct for crossover problems in speakers and low frequency problems with rooms, speaker placement and subwoofers. I agree that quality loudspeakers are not likely to need any equalization. I agree that woven screens should be the standard for reference sound in a commercial theater or dubbing situation. Skywalker Ranch is using them currently.

The fact that what Brian heard in his headphones is not matching the theater is not only the result of the mixing process and poor setup. There are numerous reasons this could be true. I believe anyone expecting commercial theaters to have high fidelity is misguided. The speakers used in those applications are more tuned to high sound levels to fill large venues than high precision sound. High fidelity sound reproduction is much more likely to be obtained in a small venue where speaker technologies like ribbons and air motion transformers can be used which have more precision than compression drivers found in commercial applications.

I setup a small screening room last year for Focus Features in NYC. They were surprised that it sounded better than Dolby in California. I have not been in Dolby's mix theater, but I expect part of the reason is the equipment we used was more for precision than high SPL coupled with a good setup. I also used very little EQ because the gear was very close to SMPTE 222M with little EQ applied. The products used included two 15" Rythmik subwoofers, JBL self powered monitor speakers, Atlantic Surround speakers, Bluesky BMC MKIII preamp, Rane for sub EQ and Motu 828 MKII D/A for the workstation.

What I find interesting is that they are not analyzing the room response in different zones of the room. They were primarily interested in the reference position. A theater is actually for an audience and not a small set of listeners. I find it is even more challenging to meet the needs of many in a theater versus a few. I also find some room shapes are much better for a group of listeners than a few. It is interesting to me this is not being investigated thoroughly. Scott and Brian discussed this a little in the interview, but the report does not address it. They should be looking a room shape, speaker placement and speaker dispersion characteristics and have recommendations in those areas as well for reference sound reproduction.
 
#39 ·
I do agree to some extent with the findings in the SMPTE report on the state of cinema sound. The current standards that we use are certainly not perfect. The way the standard is written leaves a lot of room for interpretation and even using the same tools, the way corrections are applied will effect the results. There is certainly a level of art in the science of setting up a sound system. In the more than 30 years I have been tuning sound systems, the tools and the process have evolved greatly.

Tuning with steady state pink noise with more than 4 mics averaged around the room will give very good and consistent results in rooms that have decent acoustics and speakers. If the room has unusual reverb or if the speakers have poor time domain response, then the results will fall away from ideal. In some cases, using a first arrival analyzer can help get around the problems, but it is not fixing the real issue of the poor speaker or acoustic issues. When (if) SMPTE does find a better way of tuning, we will certainly move to it. My tuning kit has gone from an analog real time analyzer with averaging filters, fed from a 3 mic multiplexer up to our current kit of using up to 8 mics all being fed in real time into a PC based analyzer which then averages the mics mathematically over the positions and over time. The system can also operate in impulse response mode and transfer function mode. We will commonly use the impulse mode to time align the crossovers for the multi-way screen speakers to get the best time domain response across the multiple drivers, and when that is done properly, the frequency response of the speaker system, before any Eq is applied, can be greatly improved.

No matter what measurement is used to come up with the tuning in the room, we currently will always follow up by looking at the pink noise in real time to make sure it still gives up what we expect. If the room is well behaved, the results are amazingly close. If the room has long reverb times that are frequency dependent, the results can end up pretty bad. And electrical corrections alone can not fix it. This is where the experience of theperson doing the tune has to step in and decide what will give the best result to the largest percentage of the audience. If they do fine a way to definitively measure and correct for this, that would be amazing and I would be happy to update my tuning kit to whatever is needed, but withthe technology we have available to us now, we do have to compromise. I do not see the current standard as wrong or even flawed. The flaw is that the method used to reach the standard is not defined tight enough and when the room is not ideal, the way engineers work around the problems is not consistent which leads to the variations in these less than ideal rooms.

We are certainly noticing that speakers that are naturally better in the time domain will result in much clearer sound. If a speaker does not sound good without Eq, Eq rarely will fix it. Most Dolby cinema processors have 1/3 octave graphic Eq sections that only give +/- 6 db on each band. I have had many theatre techs complain that they wish it had +/- 12 db like the Eq on his car stereo so he can get get the dips all the way out. WOW!! if you need more than +6 db to fix a dip there is something seriously wrong. When I dial in a good crossover, on a good speaker, in a decent room, I rarely ever end up needed even +/- 3 db of final Eq. Moving the mics around the room and looking at single positions, I like to see the worst seat (in the reasonable listening area) still falling within +/- 3 db across the spectrum.

There have been experiments with tuning a speaker either outdoors or in an anechoic, with the screen material in front of it, and then putting it in the theatre and seeing the results. The larger the room, the more the HF rolls off, and in small rooms, the LF can build up, the rest of the changes are usually quite minor unless the target room has too much or bad reverb characteristics. Chasing the ripples caused by minor room modes with a lot of Eq is certainly going to hurt the sound, and that is done all too often with the current practice. This is why some engineers end up with better sounding results than other engineers. It is not the standard itself that is badly flawed, it is how it is implemented. I have certainly updated and improved how I handle challenging rooms over the years.

I certainly look forward to any progress that will make the results better and more consistent. I do not see a document that can replace a person with experience doing the tune though. Even if we end up using different test signals and analyzers, to give a better indication of what is heard and a more accurate way of determining if, where, and what type of correction is needed, it still comes down to using the tools correctly and applying appropriate correction where needed. There will always be some rooms that just sound better than others due to the space as well as the equipment used. We do our best to make them all sound as close to the ideal environment and perfect speakers as we can. We are getting better at it, while still using the current standard as a reference. But we certainly work well past what is spelled out in the standards now when it comes to time aligning crossovers and aiming speakers. Line arrays and ribbon speakers are a new challenge. Even when the analyzers say they are tuned the same, there is a different sound to them. Speakers have a fair amount of distortion and I believe the spectrum of the distortion is most of the difference I am hearing. Larger horn based line arrays bridge the gap between conventional horns and the ribbon lines. The perfed vs woven screen issue is a huge one, but there are limit on how large of a screen can be woven as they cant have seems like a vinyl screen. Smaller rooms and 4K projectors have brought the "micro perf" screen that have much smaller holes but more of them. They seem to have much more HF roll off to them compared to the regular perfs, but in short rooms, you can see the perfs, and the pixels on the 4K projectors can create a moire effect when some perfs are in the center of a pixel vs on the edge of a pixel. On 2K projectors, there were usually a few perfs inside each pixel, so the effect was far less noticeable.

We had to go out and re-tune a room 3 times in a month as they were testing different screen, and the sound changed so much, the screen change made the room unusable until we re-tuned the system. The room has excellent acoustics and Meyer Acherons behind the screen, so the time domain was excellent for sure. Just minor tweaks to the HF parametric filters put them back in spec and brought the wonderful clear sound back.

We need well defined response and level standards, but we also need consistent ways to get there. It would take a huge document to try and detail how we apply the current standard. Much of it is learned through experience. I am happy to see this is being looked at closer, but calling the current spec totally useless is just plain wrong. The problem is not the target of the spec, it is the route of getting there that needs the work. Time domain is not even address in the spec, and for the most part, we can only adjust this between the multiple drivers of a Bi,Tri, or Quad amp'd system. It is up to the speaker designers to make drivers that behave well. Meyer has done an excellent job there.
 
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