Proper studio monitor placement and calibration is critical to get the best experience in your listening environment. Taking the extra time to set up your studio monitors will make mixing easier and ensure that your mixes translate well from speaker to speaker. Like everything in recording and mixing audio, careful preparation will give you a better result. Luckily, perfecting your mixing environment only takes a little know-how, planning, and time.
After you have properly positioned your studio monitors and listening position, it is helpful to set all the levels in your studio so that you are optimising every component. It is essential, taking the time to properly calibrate your speakers can be very valuable in this respect and will also give you a great starting point to troubleshoot or fine-tune your mixing environment.
The main purpose of speaker calibration is to ensure that a specific metered audio level in your DAW or on your mixer equals a predetermined SPL in your studio environment. Depending upon the method and reference levels used during calibration, proper calibration can help reduce unwanted noise, minimise the risk of damage to your studio monitors and to your ears, maximise the reference capabilities of different speaker types, and ensure you hear the audio as accurately as possible.
Historically, Dolby approved professional cinema mix rooms are aligned so that 20dBFS (RMS) pink noise produces 85dB SPL from each individual speaker. This level is right in the middle portion of the Fletcher‑Munson curves, and it produces an acceptable listening level in a large cinema‑like space. It's worth appreciating that this reference level requires speakers capable of delivering 105dB SPL individually to the listening position for a peak‑level digital signal — and few project‑studio monitors can achieve that.
This 85dB SPL Dolby standard has been widely adopted in other professional audio circles too, and there are references to it from numerous audio standards bodies (for example, the SMPTE's RP200 and the ATSC's A/85). Confusingly, though, it was subsequently discovered that the way in which Dolby measured the pink noise was slightly inaccurate, and so the reference level has been tweaked slightly, and the revised standard is now 83dB SPL (as measured on a full-bandwidth SPL meter with C-weighting and slow averaging from a 20dBFS RMS pink noise source).
This 83dB SPL reference level (with 103dB peaks) is perfectly acceptable if you're listening in a big space, like a cinema or a film dubbing theatre, or even a very large and well treated commercial studio control room. Unfortunately, it will be completely overwhelming in a smaller space, because the listener is inevitably sitting much closer to both the speakers and the room boundaries. The very different nature of early reflections makes the level seem, psycho-acoustically, much higher than it would be in a larger room. Consequently, the optimum reference level for smaller rooms needs to be lower, on a scale which is dependent on the enclosed volume of the room in question. You can work out the volume of a room simply by multiplying together its length, width and height
Having a consistent playback level in a sound mixing or mastering room is essential for
ensuring that all the bits and pieces you create. When you get in the habit of keeping your
hands off your room’s master level, you’ll find yourself fixing things that might have
otherwise slipped by.
To set a predictable reference level, you’ll want to use pink noise and a sound pressure
level (SPL) meter to set the output of each speaker. Keep in mind that this is only one
aspect of proper room setup. Choosing room treatments and speaker placement are
vitally important topics that are beyond the scope of this primer.
The following assumes a 5.1 surround room. You can use the same technique for a 2 or
2.1 channel stereo setup.
1. Decide what speaker calibration level you want for your room. This decides how
much headroom your system will have beyond the level of normal spoken
dialogue, by determining the physical amplitude of pink noise at -20dBFS, RMS
where 0 dBFS is assigned to the maximum possible level. The higher the number,
the higher the peak amplitude for which you’re setting the system. Assuming that
you want calm, spoken dialogue to always be at about the same level, a higher
calibration levels means more headroom above the level of dialogue. Common
selections include 85dBc SPL, which is used for large rooms such as movie
theatres, and 75dB SPL, which is used in many smaller rooms set up for television,
home theatre, or games.
2. Determine which controls you will use to set the output of each individual speaker.
If possible, put these controls where you can reach them while reading the meter.
If not, enlist a second person to adjust the controls while you measure the signal.
3. Set up a noise source that will play pink noise through your system at -20dBFS
RMS. In a Pro Tools system, you can use the Noise Generator plug-in set to RMS,
selecting Pink Noise as the type and -20 dbFS as the value. The important thing
is that it is in your system in a place where there aren’t extra pieces of gain stage
in front of the speaker: if it’s going into a mixer section that will drop it by 6dB,
getting a good reading will be complicated.
4. Determine the central listener position in your room. This should be equidistant
from your left and right speakers, and from your centre speaker unless you use a
delay on the centre. If you used ITU specs to set up your surrounds, these should
also be equidistant from this position.
5. Place an SPL meter, on a stand at this central listener position, at head height.
6. Set it to C-weighted, slow. C-weighting means that it applies a curve before
evaluating SPL that rolls off some lows and highs. “Slow” means that it uses a
longer window of time to come up with a reading.
7. Set the range on the SPL meter to the appropriate reference sensitivity
8. Play pink noise through your left speaker. Adjust its output until the meter shows
the number that you’ve chosen as your calibration level.
9. Repeat this with your centre and right speakers, one at a time.
10. Repeat this with your surround speakers. If you have more than one speaker on
either side of the surrounds, set them one at a time to 3dB SPL lower than your
calibration level.
11. Repeat this with your LFE channel, targeting a level that’s about 6dB SPL higher
than your calibration level.
Report ITU-R BS.2159-7
(02/2015)
Multichannel sound technology in home
and broadcasting applications
https://www.britannica.com/science/Fletcher-Munson-curve
http://digitalsoundandmusic.com/chapters/ch4/