calibrating a small room with 002R

[viaspiaggia]

i've set up plenty of rooms to proper -20dbFS = 0vu = 85db, and have mixed features in those rooms that i took to dub stages and they translated fine. now i'm trying to do a very fast indy film mix at my home studio (002R on a 1.6g g5 with mackie 624s). i will do 75% of the mix in this small room on this small system, and then move to a room i set up and trust to finalize the mix. so i'd like to calibrate my little room as best i can.

problem is, the 002R is permanently set at -14db. i can deal with my meters reading 6 db off if i have to (which they do), but i'm not sure how this affects my 85 calibration procedure -- if i let the -20dbfs pink noise play with no gain adjustments and adjust my monitor level to 79db it feels about right in the room - would that make sense? i use the meters for a reference but i end up trusting my ears based on knowing the room is at 85db most of the time.

i finally got my brain around the whole calibration procedure, but re-figuring it all for a source that's fixed at -14db is more than my feeble brain can handle! any help appreciated!

-adam-

[viaspiaggia]

anyone?

thanks!

-adam-

[Eric L]

Hey Adam,

I'm not sure I (or anyone else judging from the lack of replies) understand your problem. What do you mean when you say the 002 is permanently set at -14db? Relative to what? How did you measure that? What meters are you talking about? Pro Tools meters or external meters? Are you using a console or feeding some other kind of monitoring device?

I also use a 002 rack at home and use the 1/4" line outputs to feed my Blue Sky volume control. I do not use the studio outputs that are controlled by the volume knob on the front of the 002r. Using the -20dbfs band limited pink noise found on Blue Sky's website, I calibrated my room with a radio shack spl meter to 85 dB and 79dB. (Two different marks on the volume knob)

I have read your post 3 times and I can't get my head around your problem. Use the files I mentioned, make sure the track they are playing on has the volume graph set to 0dB, assign the track output to the correct 002r output and measure with your spl meter. Adjust the "volume" of the speaker you are measuring until you get the reference level you want (79dB or 85dB). Mark this level somehow. If you are using a digital console, save a preset for this new default set up.

More sophisticated monitoring devices (Martin Multimax is one example) will have a volume control with an LED that shows the reference level change as you turn it up or down. Check out dr. Sound's sticky post at the top of this forum for a refresher.

I hope this was some help.

[viaspiaggia]

hey eric. thanks for the reply, and sorry if my post is confusing. let me see if i can clarify - there are lots of posts on the DUC these days about using 002 systems for editorial for features so i think this is worth discussing.

fyi i am using the monitor outputs of the 002r which follow the front panel volume knob, i have dorrough 40c loudness meters, and i too am using the blue sky test files.

the FIRST step of calibrating a room is calibrating the outputs of your interface so that a -20dbfs sine wave reads 0vu or 1.23volts. problem is, all the outputs on the 002R are permanently set so that -14dbfs = 0vu (1.23v). so, a -20 sine wave does not read 0vu on my dorrough meters, and there is nothing i can do about it. (well i could recalibrate my dorroughs to -14 but that doesn't really help) so i can't perform this crucial first step, and i'm wondering how that affects the whole rest of the calibration procedure.

based on what my ears are used to hearing in other rooms i've set up, i'm playing that -20dbfs tone straight out my 002R and adjusting the volume level to read -79db on an spl meter, and using -6 on the dorrough as 0. i take this mix to a calibrated room in a week so we'll see what happens when i get there.

any critiques or comments or suggestions are welcome!

-adam-

[Eric L]

Hi Adam,

Thank You for clarifying. I do understand what you are saying and it prompted me to make some measurements of my own. Using -20dBfs 1k tone from Blue sky, I made some voltage measurements on the outputs of my 002r. Surprisingly, I have slightly different results than you, but this won't matter, as I will explain in a moment. But in the interest of science, here are my results. Measurements were made with Waves PAZ meter plugin and my craftsman digital voltage meter, sending signal out line output 7 and then 8 for comparison. (1-6 are currently hooked up to my speakers)

-20dBfs=0.700V
-15.7dBfs=1.23V

When I used the monitor outs controlled by the volume knob I could not get 1.23V at full volume.

-16.9dBfs=1.09V is the loudest/highest it would go.

This is why I do not use these outputs.

So now more to the point of your post and a solution. I will assume from your original post, that you do not use the analog outs for any transfers, but just deliver the Pro Tools session to the dub stage. Thus staying digital for delivery. Since we are using the analog outs for monitoring only, we can adjust the level at the INPUTS of the monitoring controller, instead of the outputs of the 002r. All we care about is that -20dBFS in Pro Tools is referenced to 79 or 85dB SPL. The electrical level of the signal is irrelevant. In your case you also would like your dorrough 40c loudness meter to be correctly calibrated. So you need to adjust the gain to the meter somehow. I have used a small mackie for this in the past. Adjust the gain so that -20dBFS in Pro Tools=0VU on your dorrough 40c loudness meter. Now measure SPL. Forget electrical measurement of the outputs. This is obviously a limitation of the 002r hardware which was never designed for this type of calibration or professional use. That doesn't mean we can't find a work around.

I hope this was some help. I am not an electrician nor a studio maintenance engineer. I specifically use the title "editor or mixer" not engineer for this reason. There are many more qualified people than me to comment on the electrical specs of the 002r hardware. Good luck.

[espron]

Hi.

I've had to deal with the exact same situation,ie use the 002 in a calibrated rom. This also applies if you are using the 96 I/O wich is also permanently set to 0VU(+4dBu)=-14dBfs

What I did was use the ADAT out of the 002 into a Apogee DA16, which CAN be calibrated. I know this may not be the most economical solution, but at least it was pretty simple, and did work very well!

Espen

[viaspiaggia]

both of these seem like great solutions, obviously for widely varying costs! looks like i've got some upgrades to do next time i have some down time.

thanks for helping me think this through...

-adam-

[David Sandwisch]

I am thinking of buying an OO2R and was wondering why it matters how the meters read on the OO2R or a 96 I/O? Shouldn't -20dbfs in ProTools just equal 79db or 85db, which ever you are using. Wouldn't you just look at the meters in ProTools on the screen since they then would be calibrated to -20dbfs = 79db or 85db? I guess I am asking why don't you just ignore the meters on the I/O? Sure in a perfect world every meter should read exactly the same but is that really necessary in the real world. I have read Dr. Sound's post on room calibration and it is a little hard for me to wrap my head around it but I think I understand the basic principles. Am I missing something here?