Monitor Calibration

Robert Katz Leave a Comment

From: Lars Hoel

…to you for an excellent presentation at the NYC AES. So now I’m a convert, determined to calibrate my Meyer HD-2w monitors to the 83 dB standard you propose. But first I notice on your web site that you’ve written this:

Monitor gains below given as a guide; your tastes may vary. As mentioned above, the Dolby Theatre standard of 85 dB SPL is very “loud” with most material when used in the home. This 85 dB is calibrated with a -18 dBFS RMS pink noise signal PER LOUDSPEAKER.

So…is this standard too “loud” for near/midfield monitoring? And what is the calibration procedure, exactly?

Hi, Lars. Thanks! (Lars is referring to my Presentation: “How to Make Better Recordings in the 21st Century by Examining the Mistakes of the 20th”, soon to be a video distributed by the AES).

Here’s everything you wanted to know and probably more 🙂

I’m going to include your letter and this answer in my FAQ at our website, at least until I rewrite the material at the website to reflect the now official SMPTE measurement of 83 dB SPL, C weighted, on a per speaker basis, with RMS measured Pink noise at -20 dBFS. You can obtain a test CD CERTIFIED to have -20 dBFS pink noise from TMH labs, or you can roll your own, if you have an RMS meter. Remember: Must be RMS measured. You can obtain a copy of SMPTE RP 200, which goes into the procedure in intimate detail, from the SMPTE.

The only thing controversial about RP 200 is making the surrounds at -3 dB each. This is the standard for the home theatre, but the ITU and other organizations have standardized on surround calibration identical to the front for music programming, television, etc. All this means is that decoders will have to properly deal with metadata when switching between music and home theatre, just another complication we’ll lave to live with. Of course, if you’re mixing stereo, then postpone this part of the agony. Also note that SMPTE uses -18 dBFS producing 85 dB SPL, which is the same monitor gain (a non-problem problem).

Next, play this pink noise on a per-speaker basis, and measure the SPL at the listening position. Check the SPL for each speaker, but don’t worry as long as they’re within 1/2 dB. Don’t try to make it equal on a per speaker basis because the exact position of your microphone is too critical to be that repeatable. Mark this position of your monitor control as 0 dB (the reference).

Now, play the non-correlated pink noise test signal out of both (front) channels simultaneously, and confirm the level goes up about 3 dB to 86. That’s an indication your speakers are in polarity with eachother. Then play the correlated pink noise test signal and put your ears between the speakers and confirm you have a nice, tight center image. The level with the correlated pink noise will be anywhere from 87 to 89 dB, depending on how correlated your loudspeakers are to eachother, room reflections, and so on. This is pretty hot for ear fatigue, so you’re welcome to turn it down and check the center image at a lower volume if you wish. If the pink noise is not centered, then slightly tweak the gain of one of the speaker/amplfiers until it is centered. It’s also good to ride the pot up and down and confirm the noise stays centered within the normal travel of the control.

Next, turn down the monitor gain 1 dB at a time (Instead of using the pink noise, you might prefer to find the rest of the points with the speakers off and with a simple sine wave oscillator and decibel meter on one of the cables to the amplifier). Mark the position of the pot at each 1 dB position until you get to -12 dB, at which point even Red Hot Chili Peppers won’t be too loud. Especially mark the -6 and -8 positions (put ’em in red). If you shoot for -6 for the vast majority of your pop and jazz productions, you will be making material that probably has an excellent crest factor, and whose loudness will in the ballpark with the vast majority of pop music ever recorded. -8 will be a good position to try for more limited range material that you will be sending direct to broadcast. It will cause you to tend to use more compression, but won’t be so bad.

YES—The 0 dB gain IS HOT. It will only be suitable for wide dynamic-range material, symphonic material, my Paquito recording, and some material that was recorded with little or no compression or limiting. But we have to have a reference somewhere, and the 83 dB reference, your mark at 0 dB on the control is the best one we have.

Bob

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