calibration in relation to level

[meathman]

I know there are multiple posts on the forum about this issue, but I have yet to find one that clarifies these basic questions about calibration and monitoring/ delivery levels.

So in film, the standard is to calibrate to -20. Im assuming this means 0VU =
-20dB....With this said, if I get a spec that says the average dialogue level should be at
-27, does this mean that on my meters I would try and hit -7 (since im calibrated to -20 already) what if I was calibrated to -18? Does this mean that -27 would infact be -9?

Also, when there is a TV spec that says levels cannot exceed -10dB, will -10 really be -10 or will it be proportionate to my calibration level? What happens if I deliver the mix at -10 while calibrated to -20 and they play it back on a system calibrated to -18? Anything?

Finally- If Im working on a system that is cal to -18 and do a mix that keeps pretty hot (gets up to zero on peaks) when it is played back on a dub stage or system calibrated to -20, will it be clipping 2dB over?

Thanks in advance

[jacobfarron]

f I get a spec that says the average dialogue level should be at
-27, does this mean that on my meters I would try and hit -7

No. Check you spec - it's probably referring to dialnorm value measured LeqA (or maybe BS.1770 at this point)

levels cannot exceed -10dB, will -10 really be -10 or will it be proportionate to my calibration level?

It is really -10dbFS. Everyone should be calibrated to the same reference level.

What happens if I deliver the mix at -10 while calibrated to -20 and they play it back on a system calibrated to -18? Anything?

First of all, what do you mean deliver the mix at -10. -10 what? As an average or peaking? What meter ballistics? I'll assume you mean the peaks are at -10dBFS.

The answer is, it depends on how your system is calibrated and how you are delivering the mix, and how the people you are delivering your mix are calibrated. Only your outputs and inputs can be calibrated - these can potentially be connected to decks to layback to, hardware meters, and/or monitors. Further down the chain, the monitors can (and should) be calibrated so that your reference level reflects approx 79dbSPL (TV) or 83 to 85dbSPL (film).

What exactly in your system is calibrated to -20dB? Are the outputs on your Digi interface still factory calibrated for -18dbFS? Most studios re-calibrate so -20dbFS equals +4dBu which equals 0VU which equals 1.23 volts.

Here's the fun part - if those outputs are going to hardware meters or to a deck to layback to - then you can be referencing the wrong levels, or sending the wrong level to tape (which would be easy to fix - send tone from your PT rig and line it up at the desired level on the deck). If those outputs are only going to the monitor chain, then you can still deliver the correct levels, you'll just be hearing them inacuratly. If everything you do is inside the box, then it's not much of an issue. The plugin meters always reflect the same value.

If Im working on a system that is cal to -18 and do a mix that keeps pretty hot (gets up to zero on peaks) when it is played back on a dub stage or system calibrated to -20, will it be clipping 2dB over?

Others are more qualified to speak about this than I. As I understand, continuously peaking at 0 for theatrical presentations is not only inappropriate, but can cause damage.

Anyone feel free to elaborate or correct any errors I may have made.

[philper]

Originally Posted by meathman

I know there are multiple posts on the forum about this issue, but I have yet to find one that clarifies these basic questions about calibration and monitoring/ delivery levels.

So in film, the standard is to calibrate to -20. Im assuming this means 0VU =
-20dB....With this said, if I get a spec that says the average dialogue level should be at
-27, does this mean that on my meters I would try and hit -7 (since im calibrated to -20 already) what if I was calibrated to -18? Does this mean that -27 would infact be -9?

Also, when there is a TV spec that says levels cannot exceed -10dB, will -10 really be -10 or will it be proportionate to my calibration level? What happens if I deliver the mix at -10 while calibrated to -20 and they play it back on a system calibrated to -18? Anything?

Finally- If Im working on a system that is cal to -18 and do a mix that keeps pretty hot (gets up to zero on peaks) when it is played back on a dub stage or system calibrated to -20, will it be clipping 2dB over?

Thanks in advance

Are you sure that that -27 figure isn't actually a "dialnorm" (long term average) setting? -20 often is calibrated to 0VU, and when a broadcaster says -10 os the limit they mean -10 dbfs, where "0" is not "0 VU" but digital "0", ie clipping. The stickies at the top of this forum (Georgia et al) explain this better than I can.

Philip Perkins

[meathman]

Thanks for the info.

Dialnorm value measured LeqA (or maybe BS.1770 at this point): Can you please explain this? By Dialnorm what do you mean? The RMS value of the Dia?

I have calibrated my 192 to -20 dB. I noticed in other similar posts people say they often shoot for DIA at an average of -20dB. This is where I am confused. is -20 dB in fact 0VU since thats what I am calibrated at, or does it actually mean -20db DOWN FROM 0VU (and if so would that be -40 dB in relation to the calibration - do people talk about it that way ever?)

jacobfarron as you said if I do a mix while calibrated to a different level than the recipient (for ex if I was at -18db and they were at -20db) IN THE BOX, as you said the levels will be correct, only i will be hearing them inaccurately. So then in that case why should editors and sound designers who are not mixers and who stay in the box bother calibrating their interfaces to -20? Would it matter at all, would it make a difference? Would I have to worry about my levels at -18 clipping their system at -20 (since they would have less headroom?)

Thanks again

[danijel]

Originally Posted by meathman

Dialnorm value measured LeqA (or maybe BS.1770 at this point): Can you please explain this? By Dialnorm what do you mean? The RMS value of the Dia?

You can find those things in Geo's Sound Post corner if you search.
Dialnorm is also very well explained here: http://www.linearacoustic.com/pdf/NAB-05-18.pdf

Originally Posted by meathman

I noticed in other similar posts people say they often shoot for DIA at an average of -20dB.

That was Georgia's levels as seen on PPM meter, and she's talking -20dBFS. Some info about PPM : BBC Radio Resources // Programme Delivery // Glossary

[meathman]

thanks for the info - very helpful.

So what im getting from this is that 0 dB does not change -20db is always -20db BELOW 0 regardless of what you are calibrated to (-18db, -20db, etc)

Right?

[jacobfarron]

So what im getting from this is that 0 dB does not change -20db is always -20db BELOW 0 regardless of what you are calibrated to (-18db, -20db, etc)

Right?

Yes, -20dBFS is always 20dB below 0dBFS - however do not confuse 0VU with 0dBFS.

So then in that case why should editors and sound designers who are not mixers and who stay in the box bother calibrating their interfaces to -20? Would it matter at all, would it make a difference?

Although I think it's incredibly important to be on the same reference level and understand the technical specs- It does not matter in the situation you outlined. Just like you actually don't have to use house blackburst for sync when everything you're doing is in the box and file based. However, I would venture to say that most studios, mine included, don't want to limit a PT system so that it can't be used in as many configurations as possible.

Would I have to worry about my levels at -18 clipping their system at -20 (since they would have less headroom?)

In the box, you both have the same amount of headroom - you're just starting at different spots on the scale. The problem will only come into play depending on what medium you record the mix to, and if you correctly specify and set the levels. If you layback analog to a deck or multitrack and do not correctly line up your tones then it's possible to clip. If you layback AES it's a one to one digital transfer so no, it won't clip.

IE 1) You are calibrated for 0VU to equal -20dBFS and your mix goes all the way up to -1dBFS. You have tone at -20 in PT. Now, you lay this off analog to a deck - only you line your tone up to -18dB on the deck. Now the peaks on the deck will clip by 2dB.

IE 2) You are calibrated for 0VU to equal -18dBFS and your mix goes to -1dBFS. You have tone at -18. You lay this off analog to a deck and set the tone to line up on the deck at -20. Now your peaks on the deck are at -3dB.

Both of these examples are a bit ridiculous. Simply line up the correct reference level and everything will be fine. Again, if it's AES - there will be no difference in level.
You should try to pick up a few books and do more research as you get time.

[mikevarela]

What alot of these guys are getting at, is that you need to configure your system first, then find spec, then mix accordingly.

I had questions with this a while ago, so maybe this will help (thanks Danijel and Georgia)

You need to calibrate your room so that you mix at a consistent calibrated level at all times. This means that you need to find your appropriate level (85dbspl film / 82dbspl film smaller mix room / 79dbspl tv mix). you find this by going to radio shack and buying an SPL meter, the analog one! then you sit in the sweet spot with the meter mic facing forward, slightly upward and shoot a pink noise audio file out one speaker at a time (download this from bluesky's website) calibrate each speaker first so that they all fire the same reading, then calibrate your volume knob on your monitor controller so that your spl meter reads one of the preferred values above. when your meter reaches one of the values above, mark your monitor controller volume knob at that spot. In fact you might as well calibrate for all three of those specs.

you can and probably also should have your room eq'ed for the sweet spot. you can do this by reading into RTA mics and eq's. In essence you eq the feed from monitor controller to speaker and calibrate your room so that you receive an even tone at the sweet spot, minus room modes and other issues that normally plague rooms. Genelec makes such a device, as does Ik media.

Once your room is calibrated.

Then make sure that your meters (software or hardware) are calibrated. most engineers work at a spec of -20dbfs = 0vu, which means that we calibrate by viewing a vu meter 0 as -20dbfs below digital full scale, in essence leaving 20dbs of headroom.

now, when someone asks you to limit at -10 they mean no signal over that level dbfs, so you stick a limiter at that mark.

if someone says to mix average -27, they mean -7 VU or -27 dbfs. Because you now have a calibrated room, you mix by ear. when you set your monitor controller to that mark, you mix by ear and taste. obviously dialog is king, so that becomes a little hotter, though most of us mix DIA around -27 to -20 or -7 to 0. listen to the latest CAS speech at the top of the forum, it'll help with some of the explanations, especially dialnorm.

specs always takes precedence, so if you mix for broadcast and they say limit at -10, do it. but under that -10 is all up to you. this is where we get into discussions of loudness wars and preferred mixing etiquette. if you slam everything up against -10, then it'll be loud, but annoying.

Dialnorm refers to the average level of dialog mixed in a program and is measured usually by leq-a or more recently the ITU standard, again listen to the CAS speech.

the art of mixing come only after you achieve a calibrated system, then you're free to make artistic decisions. without a calibrated room, your either guessing or mixing to meters, both of which are bad decisions.

hope this helps,

I'm sure some of you might want to chime in too

[starcrash13]

Originally Posted by meathman

thanks for the info - very helpful.

So what im getting from this is that 0 dB does not change -20db is always -20db BELOW 0 regardless of what you are calibrated to (-18db, -20db, etc)

Right?

dB is always relative to something else. To give absolute figures, use the suffix FS (full scale) which means that a number of dB in relation to full scale digital zero (all 1's, no zeros).

For example, -20dB is not very useful on its own, but -20dbFS means 20dB below digital zero.

Sometimes people will leave off the suffix to save time and it's assumed that others know what they mean from the context of the situation.

[dr.sound]

Read This;
NEW UPDATED Room Calibration for Film and TV Post - Digi User Conference

It is "Room Calibration for Film and TV". Read it!
Use the links in the "Room Calibration" Thread !

[kk@jamsync.com]

Originally Posted by meathman

thanks for the info - very helpful.

So what im getting from this is that 0 dB does not change -20db is always -20db BELOW 0 regardless of what you are calibrated to (-18db, -20db, etc)

Right?

0 dB FS does not mean very much unless it is matched to a specific dB SPL. Only if you are cal'd all the way through: -20 dB FS = 0 VU = +4 dBu = 85 dB SPL (for example) do the individual levels make any real listening sense that will translate to other playback environments.

For example, if you were to change the middle section to say, broadcast terms...
0 VU = +8 dBu, then although you could still cal to 85 dB SPL, the intermediate electrical measurements would be different.

You have to look at each term of the equation and ask, "why am I setting this level this way?" Is it an electrical level derived from a sine wave or from pink noise? Is the noise bandwidth limited or not?

There are many, many questions to be answered when you are setting up a system that needs to translate to other playback environments.

[kk@jamsync.com]

Originally Posted by starcrash13

dB is always relative to something else. To give absolute figures, use the suffix FS (full scale) which means that a number of dB in relation to full scale digital zero (all 1's, no zeros).

For example, -20dB is not very useful on its own, but -20dbFS means 20dB below digital zero.

Sometimes people will leave off the suffix to save time and it's assumed that others know what they mean from the context of the situation.

And it's important to note that dB FS increments do not equate to dBu or dBv or dB VU!

[georgia]

Just to go back to one of your questions. If you do not calibrate your room correctly, your mix, when played back in another properly calibrated room or theatre will play at a different level that what you would expect. For instance if you didn't calibrate your room and mixed a project with the monitor level at a comfortable setting and your mix was recorded at high levels to the print device ( tape, files, optical, whatever ) your mix would be insanely loud in a theatre. If you had the monitor level turned up too high and you mixed the same project, you would probably end up with a print that was too quiet and the output in the theatre would be very low. So, as the gang here explained quite well, you need to understand what you are trying to do, and calibrate accordingly. Marty ( Dr. Sound ) suggests you read the calibration thread. I agree. If you still do not understand what, why and how to calibrate and you are going to do a project for broadcast or theatre, then hire a professional to calibrate your room. At the very least, TEST your mix in a calibrated room when you are done to verify levels and balance.


cheers
geo

[meathman]

thanks so much guys for all this helpful information. I now understand the importance of having a calibrated room and plan on going through the necessary steps to make mine to spec.

[rhumphries]

Originally Posted by kk@jamsync.com

And it's important to note that dB FS increments do not equate to dBu or dBv or dB VU!

Sorry to nit pick here, and I may have simply misunderstood you.

Are you saying that by changing the level in dB FS by X dB that it does not equal a change of X dB in the other scales? That is not how I've understood it to work, and and a quick search for a dB conversion calculator confirms my belief. i.e if -20dB FS= 0dB VU= +4dBu, then -21dB FS = -1dB VU =+3dBu. Right? Or did I completely missunderstand your point?

-Richard

[kk@jamsync.com]

Originally Posted by rhumphries

Sorry to nit pick here, and I may have simply misunderstood you.

Are you saying that by changing the level in dB FS by X dB that it does not equal a change of X dB in the other scales? That is not how I've understood it to work, and and a quick search for a dB conversion calculator confirms my belief. i.e if -20dB FS= 0dB VU= +4dBu, then -21dB FS = -1dB VU =+3dBu. Right? Or did I completely missunderstand your point?

-Richard

Depends on whether or not you are using sine or square wave or pink noise for the audio program and whether or not you are measuring peak or RMS. It becomes especially important when you are integrating commercial playback devices into a cal'd playback system. dBv increments are not dBu. I should have said "do not necessarily equate due to difference in measurement techniques."

There must be somewhere on Google my various postings on RMS vs Peak meters, but as a start I suggest the wikipedia article below (posted by someone else)...

dBFS - Wikipedia, the free encyclopedia

[meathman]

quick question about specifically calibrating a digidesign 192...

where do I hook up the voltmeter to read the voltage...Can i just plug it into the female holes on the db-25 connection on the back, or will i need a db-25 to xlrm snake and measure from the 2 and 3rd pins of the xlr for each channel..

Thanks

[jacobfarron]

If you can / want to count the holes on the DB25 it's possible... but it would be a real PITA. I use a snake, open up one of the connectors, and and put alligator clips on pin 2 and 3. Works well for me.

[kk@jamsync.com]

Originally Posted by meathman

quick question about specifically calibrating a digidesign 192...

where do I hook up the voltmeter to read the voltage...Can i just plug it into the female holes on the db-25 connection on the back, or will i need a db-25 to xlrm snake and measure from the 2 and 3rd pins of the xlr for each channel..

Thanks

I do it at the patchbay with a tt-to-alligator clip setup. That way I don't have to freeze myself in the machine room.