Validity of X-curve For Cinema Sound

[Andysu]

Dolby Stereo CP200 in selected THX cinema

 

[Deleted member 49933]

Dolby measure it using RTA / pink. And yes the goal is flat response from the speakers. (I.e. In a lot of cases, once a speaker system is calibrated to be "flat" in a large room, it'll be fairly close to the x-curve, but there are a ton of variables that can throw the correlation out if you're unlucky, obviously)

Hi. I've found this post on Avid community:
https://duc.avid.com/showpost.php?p=2671263&postcount=304

Is that true? The new target now is 82.5 dBA with the X curve?

 

[audio2920]

Well, I've never seen it done that way but it makes some sense I guess. If you're in a room where it makes sense to be on X-curve though, then the C-weighting at 85 should achieve the same level, unless you have FR issues. So I'm not sure it's a material change in spec..?

I guess it's more just a quick and dirty way of discarding upper and lower frequencies if / incase they're out of whack (for whatever reason) and make sure the dialogue band is broadly where it should be.

 

[Andysu]

great names in sound , JBL professional cinema , Dolby Stereo " x curve 85dB ref " , lucasfim ltd THX sound system and pioneer laserdisc

 

[Deleted member 49933]

So, early this year, I rescanned the English DTS-HD MA of Tenet and it's indeed around -11 LUFS.

Now, I'm back in Germany for work and was checking some pre-Dunkirk UHDs of Nolan's on caps-a-holic and realized that the French and German DTS-HD MA tracks have lower bitrates compared to English (~2 Mbps vs 4).

I won't be able to scan those in Audition 'til Christmas time, so could any of you compare them in a listening test or speculate on the reasons for this?

Maybe they put together nearfield and farfield mixes on the same disc?

Thanks.

Eh, I forgot to give an update on this.
The difference between the 2 Mbps and 4 Mbps tracks is the bit depth (16 vs 24).
No difference in LUFS.

 

[ackdigital]

My pleasure and welcome to the forum Anton.

As to your question, it is the classic "old guard." Compliance with X-curve using the horrid 1/3 octave equalizer is part of getting Dolby Certification for movie sound. That being a big deal, folks are reluctant to change anything and lose that certification. And there a lot of old-timers protecting their past with vengeance. They complained bitterly about my article above but had no science to counter any of it so the editor of WSR proceeded with publishing my article as is. They have really slowed down progress here clinging to decades old folklore on what a neutral system should sound like.

Hi Amir,

Great article, but why be harsh to « old-timers »? Granted, science is about numbers, experiments and results, however sound and how each one of us perceives it goes far beyond numbers. As you correctly pointed out it’s the sum of many factors and there is one we cannot mesure, psychoacoustics. Maybe Ioan Allen’s methods were far from perfect, but for some reason there is some truth about the x-curve, one that cannot be proved with measurements and numbers.

I am a re-recording mixer and I mix content « far field » (about 4,5 meters distance from screen). My studio is quite small though, well treated with absolutely no reverberation (not a very good thing). So when I started mixing there I just calibrated properly the sound system (9.1.6 dolby atmos) and thought that applying the x-curve wouldn’t be necessary. When I tested my first mix to various playback systems, from cinema venues to near field 5.1 and stereo setups and even living rooms, I found a lack of high frequencies and low frequencies being a bit shy. So I recalibrated my system with the x-curve and now I have a much better translation to most configurations, without having to remaster for each medium.

I’ve also made several observations: watching (and hearing) a two hour film in the cinema anywhere between dolby level 6 to 7 (a rarity) without x-curve can be extremely fatiguing causing severe headaches. I was able to correlate this years ago at a very big and prestigious IMAX venue in France. They had just updated their sound system and calibrated using presumably the x-curve. Presumably because the personnel there thought the sound was a bit « muffled « , so they did a new calibration, much brighter compared to the previous one. So we checked a 40min film. For the first five minutes it sounded great, hearing all the details from the soundtrack was thrilling. However, about 15-20 min in the film my ears started being in pain thus losing focus on the film and about the end it became no less than a torture. My input to the guys was « please revert to the previous settings ». Imagine that for a two hour feature film…

Can I explain this with numbers? Absolutely not, but this does not cancel the experience nor the validity of that mysterious x-curve effect.

 

[ackdigital]

@amirm (and others), does that mean a lot of movie content is recorded/produced with a de-emphasis on high frequency content to more accurately fit the X-curve? Seeing as it was concluded pretty much all theatres don't show natural high frequency roll off as severe as what the X-Curve demands, then does that mean that movie content is made with a de-emphasis of the high frequency content in order to make it easier to EQ in the theatres to match the X-Curve? (When I say de-emphasis of high frequency content I guess I mean artificial reduction of high frequency recording levels during recording/production, so that it fits the X-curve more easily in theatres).

I'm asking this because I've noticed since EQ'ing my speakers to various House Curves or variations of them, that Movie content seems to be High Frequency Poor, as in the high frequencies seem under represented in contrast to the bass - which has resulted in me using either a near "Flat Curve" or "Half Harman Curve" (half the bass, half the treble loss) for movies, whereas for music content I know I like the Full on Harman Curve the best (increased bass/reduced treble). Makes me conclude that the high frequency portion of movies is de-emphasised to more accurately fit the unnatural X-Curve?

EDIT: or a problem associated with my thinking here...movie theatres would calibrate their theatres using I guess frequency sweeps to fit the X-Curve, and if that was the case then you'd want the playback source (movie) to be recorded linearly across the frequencies then, because you wouldn't want to EQ twice so to speak? So that would go against my theory that movies are recorded/produced with lower high frequency recording/production levels. Hmmm, anyone from the industry shed any light on this? I've just noticed that movies seem treble light when played back at home in comparison to music, hence my choice of different house curve for movies vs music.

EDIT #2: and another thought, my movie experience at home is from over the air broadcasting on terrestrial TV here in the UK, and also Amazon Prime streaming...is it possible that these broadcasters also provide some kind of colouring to their audio in terms of bass/treble boost/reduction....and also would the movie soundtrack given to these broadcasters from the movie companies even be the same format in terms of frequency response as the soundtrack that is released to cinemas/movie theatres? So a number of variables that might invalidate my comparisons & conclusions I was making earlier in the post. Anyone in the industry shed some light on all of this?

Hi!

I’ll try try to answer some of your questions…

1. A printmaster leaving the dubbing stage for a theatrical release is quite rich in high frequencies because of the x-curve, if you listen it on a nearfield system. So when played back in the theater it’ll sound as expected.

2. A theatrical print usually sounds different from a bluray/dvd/tv/streaming release. It is remixed/remastered nearfield and this changes the EQ curve and compression for compatibility with consumer playback systems and listening environments. The dynamic range is also much more contained.

3. Broadcasters and streamers give specific guidelines concerning the deliverables that must be respected and as far as I know they do not apply any further processing (except the broadcasters as they use compressors/limiters on the output).

For a « consumer » playback system properly calibrated, the x-curve is irrelevant.

 

[Robbo99999]

Hi!

I’ll try try to answer some of your questions…

1. A printmaster leaving the dubbing stage for a theatrical release is quite rich in high frequencies because of the x-curve, if you listen it on a nearfield system. So when played back in the theater it’ll sound as expected.

2. A theatrical print usually sounds different from a bluray/dvd/tv/streaming release. It is remixed/remastered nearfield and this changes the EQ curve and compression for compatibility with consumer playback systems and listening environments. The dynamic range is also much more contained.

3. Broadcasters and streamers give specific guidelines concerning the deliverables that must be respected and as far as I know they do not apply any further processing (except the broadcasters as they use compressors/limiters on the output).

For a « consumer » playback system properly calibrated, the x-curve is irrelevant.

Thanks for the reply, but that was indeed a post of mine from 2020, but that's fine. I no longer use Room EQ across the whole frequency range, and instead I just use an Anechoic EQ to make my speakers Anechoically Flat using Amir's measurements of the JBL 308p Mkii, and then I use Room EQ up to about 300Hz, so my speakers are essentially just Anechoic Flat speakers in a living room, but I did put in the Harman hump in the bass as part of the Room EQ, and generally my speakers want to follow the downwards tilt of the Harman Curve anyway (on their own) probably since Harman was based around Anechoic Flat speakers in a room. Yes, so that setup is fine for music & movies now for me.

 

[Rockerilla77]

Huge thread here! There's a lot to learn. Do you know where to get this reference given in the original post?

[17] Subwoofer / Low Frequency Optimization, Majidimehr, Widescreen Review Magazine, May/June 2012, http://www.madronadigital.com/Library/BassOptimization.html

The link doesn't work