As promised, this is a quick little guide for people participating in the Sound Design Challenge on how to calibrate the listening level of your monitors (speakers). Meet your friend, the Sound Level Meter!
This device measures the overall loudness of acoustic waves in the space it occupies. It is somewhat directional, and that silver looking nub at the top of the image is the microphone for the device. These come in a variety of makes, sizes, and cost levels. The particular meter I have was bought at Radio Shack a number of years ago for about $30. The price has gone up in the last few years apparently, but the same device can be found here. If the new $50 price tag seems a little steep to you, don’t worry. There are a variety of these devices available on the market, and one of them is bound to fit into your budget. Just take a look at these listings on Amazon; from $25 up to $600.
You’ll need two things to calibrate your monitors, a pink noise file and one of our fancy SPL meters. These meters come with a number of different “weighting” systems built into them. The industry standard is to use a “C-weighted” curve (refer to your meter’s manual to learn how to select weighting), “slow” setting. If your meter does not have that, it’s ok to use “A-weighted” instead; it’s better than nothing. Pink noise, as you may or may not know, is a signal that has equal power across octaves. [ed. Special thanks to Dustin Berta for pointing out my earlier stupidity on this.] In particular, you want a -20dB (full scale) pink noise file. You can get these a number of ways. The quickest way may be through your DAW (such as Pro Tools’ Signal Generator plug-in), but you can also download a useful set of test/calibration files from Blue Sky (this page is great if you really want to get into the nitty gritty of calibration) or purchase a reference CD when they’re occasionally available from AES (I bought one at the Nashville conference last year for $10). What we want to be able to do when calibrating, is measure one channel/speaker at a time. So, route that pink noise to just one of your speakers and you’re ready to start.
First, we need to hold the meter in such a way that minimizes the effect our body has on the measurement. To do this, lay the meter flat on your palm perpendicular to your hand, and hold you arm straight out in front of you. From your listening position, point the meter at the active speaker. This means the speaker is going to be to your side. You should look fairly similar to this image:
Now, I was holding the camera about level with my head; notice that meter is at about the same height. From this position, I can easily see the display readout, but my body will have less effect on the measurement.
At this point I need to mention that there are two primary standards that we deal with for listening level when mixing for film and video. For television, we want the speaker’s output of that -20dB-fs pink noise file to read 78dB-SPL on our meter. For film, the standard is 85dB-SPL. To actually calibrate the monitors to one of these levels follow these steps:
- Load your -20db-fs pink noise file into your DAW.
- The volume on the track for this file (in the DAW) should be at 0/unity. Do not adjust the volume on the track up or down.
- Route the output to one speaker only.
- Hold the meter as previously described, and determine the speaker’s current playback level.
- Adjust the gain/trim for that speaker up or down towards your spec (78dB-SPL for TV, 85dB-SPL for film). If you have “active” speakers make this adjustment on the speaker itself. If you have “passive” speakers make this adjustment at your power amp. [Somesystems may have a function that allows you to make these adjustments for each individual speaker without searching for its trim control, such as the Avid Icon/X-Mon system for Pro Tools that I have at work]
- Repeat steps 4 and 5 until the speaker’s output stays at your preferred playback level.
- Repeat steps 3 through 6 for the remaining speakers in your system [note: if you have a sub woofer, you'll want to get the band limited pink noise file offered on the Blue Sky site.]
That’s all there is to it. Unless you’re in a massive room, it’s not in your best interest to use a film spec playback level (85dB-SPL); and I would suggest you use the television spec instead (78dB-SPL). [Chart with room size and appropriate calibration levels below.] It is strongly encouraged that you calibrate your monitor levels before participating in the Sound Design Challenge. Even if you’re not participating, I’d still recommend it; at least you will be certain that your speakers are all producing the same levels. That means your spatial ideas (stereo, 5.1, etc.) will be more likely to play back correctly on other systems. You should also regularly check you calibrations to make sure nothing has changed. It’s just one of the many steps we need to take to maintain the quality of our mixes.
Update: There’s also some great info in this posting over on the Avid Audio Forum (formerly DUC).
Addendum:What level should you calibrate to for different size rooms!?
This info section comes from a secondary post I wrote nearly two months after writing this initial tutorial. It can be found here. I’m adding this info because it may [should] be useful to some [all] of you. ;)
Essentially, the smaller your room is, the lower your listening level should be. It’s just a simple fact of the way we hear that higher levels in smaller rooms are going to give unnatural (well…maybe supernatural) emphasis to different frequencies. Listening at appropriate levels will help maintain the integrity of your mixes as they move from one system to another, in rooms of varying sizes. It’s the main reason I suggested using 78dB-SPL in the previous tutorial. Unless you’re in a mixing stage that is the size of a movie theatre (and has similar acoustics), 85dB-SPL is too loud for you to be mixing at.
In the interest of keeping this simple I’m going to stick with their basic guidelines for small rooms. They have an expanded spec for really small rooms, but it’s going to be beyond most of our abilities to replicate it. Their suggested listening levels for rooms used in final mixing are:
- Greater than 20,000 cubic feet (566 cubic meters) - 85dB-SPL
- 10,000 to 19,000 cubic feet (283 to 565 cubic meters) - 82dB-SPL
- 5,000 to 9,999 cubic feet (142 to 282 cubic meters) - 80dB-SPL
- 1,500 to 4,999 cubic feet (42 to 141 cubic meters) - 78dB-SPL
- Less than 1,499 cubic feet (41 or less cubic meters) - 76dB-SPL
If you’re not sure how to determine the cubic dimensions of your room, measure the central axis of it’s length, width and height and multiply all of those figures together (length x width X height), and that will give you the cubic feet of your room. I say measure the central axis, because if you’re room is an odd shape, it will at least get you in the ball park. If that ball park is right on the line between two ranges, I’d suggest you round down to the lower level.
So, if my room was 11ft x 13ft x14 ft (these numbers chosen at random), that would yield a cubic dimension of 2002 ft. I’d then want to calibrate my room to 78dB-SPL.
As always, if you’re smarter than I am (which isn’t very hard, I assure you), and you’ve spotted something in my text here that is inaccurate or doesn’t make sense, please let know. I’ll be happy to make changes and credit you for them.