Film-Tech Forum ARCHIVE: EQ curve

This is topic EQ curve in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=003327

Posted by Antonio Marcheselli (Member # 373) on 04-22-2002, 01:53 PM:

Hi everyone,

I need to know the correct curve to equalize stage channels. I need to know where the freq. response start to drop and how much.

Thanks!

Antonio

Posted by Manny Knowles (Member # 1171) on 04-22-2002, 02:08 PM:

Hmm...I was taught to go for as flat a response as possible (but without "over-EQ-ing").

------------------
And, hey! Let's be careful out there.

~Manny.

Posted by Antonio Marcheselli (Member # 373) on 04-22-2002, 02:17 PM:

I knew that there is a specific curve to follow and that the "flat" response was referred to that curve.

Antonio

Posted by Brad Miller (Member # 2) on 04-22-2002, 02:50 PM:

20hz to 2Khz flat, then down 3db per octave up to 20Khz.

Posted by David Stambaugh (Member # 1102) on 04-22-2002, 02:55 PM:

Stupid newbie question: Why the rolloff at upper frequencies? I would think that since the speakers are behind a perforated screen, which will affect the response, you would maybe want a boost instead of rolloff to compensate for high frequency loss. ?? Is what you're referring to called the "B Curve" or something like that? If a theater is following THX guidelines, is the desired response curve the same (I could probably look that last one up myself)? Sorry, enquiring minds want to know.

[well, I knew it was the "some letter" curve]

Posted by Gordon McLeod (Member # 33) on 04-22-2002, 04:34 PM:

Back a long time ago Bell Labs discovered in a large room the electrical acoustic curve to playback of music compared to the live event in the same room had a roll off to it
In a large room it worked out over the years to being flat to 2K and then rolling off 3 db per ocatve. In smaller rooms less roll off and in gigantic rooms more roll off. This is also related to the reverberation time and we will not go there here
Despite what some claim the X curve as it is now referred to is an ISO standard

Posted by John Pytlak (Member # 331) on 04-22-2002, 04:37 PM:

The pertinent standard is SMPTE 214M-1999:
http://www.smpte.org/smpte_store/standards/index.cfm?scope=1&stdtype=smpte&CurrentPage=8

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by David Stambaugh (Member # 1102) on 04-22-2002, 04:58 PM:

Interesting. "SMPTE 214M-1999: for Motion-Picture Film (35-mm) - Photographic Audio Reproduction Characteristics. This standard specifies the electrical frequency response characteristics for photographic audio reproduction in motion-picture control rooms and indoor theaters."

Does that refer only to optical soundtracks? Does digital follow the same specs? Mag? Just wondering, since the spec specifically identifies optical playback. Unless they mean "photographic" in the more broad sense of the word, like movie sound in general.

Posted by John Pytlak (Member # 331) on 04-22-2002, 05:18 PM:

There are separate SMPTE Standards for magnetic sound.

e.g., SMPTE 208M, SMPTE 217, etc.

Posted by Antonio Marcheselli (Member # 373) on 04-22-2002, 05:30 PM:

Brad

20 to 2000????

I always saw flat to 12.000

Today is the day of news...

Bye
A

Posted by Gordon McLeod (Member # 33) on 04-22-2002, 06:19 PM:

John that standard I believe is the A chain standard for optical and there is a mag one as well as it specifies up to the main fader the room accoustic response is after that
the x curve is ISO2969

Posted by David Stambaugh (Member # 1102) on 04-22-2002, 06:37 PM:

Did some searching, found some info on ISO 2969. It's based on psycho-acoustic testing of human hearing in near and far soundfield situations. Applies only to large venues such as movie theaters. It rolls of the high frequencies as Brad and Gordon said. (Not that they need me to confirm what they said

)

THX seems to take issue with the ISO 2969 curve, but it isn't clear from what I read whether they're talking about THX re-eq'ing in a commercial theater, or in a home theater.

Posted by Antonio Marcheselli (Member # 373) on 04-22-2002, 06:38 PM:

Brad,

Ignore my previous message.
Ok, flat to 2k.
But about the 20hz... I saw on CP500 that frequencies should start to drop at 50Hz.

Who is right?

Bye
Antonio

Posted by Gordon McLeod (Member # 33) on 04-22-2002, 07:42 PM:

THX supports the ISO curve for comercial theatres

Posted by David Stambaugh (Member # 1102) on 04-22-2002, 07:51 PM:

Based on the difference in sound at the theaters here, seems like one of them has to be deviating from the X curve. Cinemark's screens all sound like the high frequencies are rolled off. They are not crisp and they lack detail. Regal on the other hand sounds very crisp and has more detail. These 2 locations are very different. Wonder which one is more correct. The Regal theater was originally THX-certified but that was dropped a few years ago.

Posted by Steve Kraus (Member # 476) on 04-22-2002, 09:54 PM:

Going back to the prior comment about speakers being behind the screen, naturally all the measurements are taken as the room is normally constituted so any loss from the screen is already taken into account in the EQ. If you removed the screen you'd have to re-EQ as there would be too much high end.

Posted by David Stambaugh (Member # 1102) on 04-23-2002, 12:05 PM:

I wasn't expressing myself very well and I also made the error of assuming that the room would be EQ'd for flat response. I was thinking of the equalizer settings, not the actual resulting room EQ.