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Calibration of Audio Playback Levels

Calibration of Audio Playback Levels for Film, TV, Video explained in basic terms

Console knobsIn order to create post production mixes that translate well to consumer systems, calibration of  your system’s  playback  level is important. It is also important to do this if you are creating music that will be passed on to other editors for use in film, TV or video. I intend to give a brief guideline here for calibrating your listening environment in a small to medium sized room, such as an edit suite. The tuning of a room is beyond the scope of this article.

For film work (usually done in larger rooms), a pink noise at reference level should be used to produce a sound pressure level of 85dBC for each of the front channels. Taking readings for left, right and center speakers. For surround speakers, a lower reading of 82dBC is used. Generally -20dBFS is used as the “0” VU reference level point ( in the USA for example), though in some countries ( Europe, New Zealand, Australia for example) -18dBFS is used as the reference, and if you are working in those countries you should use that level in your calibration procedure.

For television and video work, which is often done in smaller rooms, a lower reference level is used. This is most often done at 79dBC for each of the speakers in a smaller edit suite room. In mid sized rooms such as pre-mix rooms this level is often set a bit higher, for example 82dBC.

The procedure for calibrating the playback level is as follows:

You will need a sound pressure level (SPL) meter to take readings from the mix position in the room. Set the meter to a  “C” weighting curve, and a slow response time. You should hold the meter in the same position at the place where you normally sit when mixing, when you are taking the reading from each speaker. It’s a good idea to hold the meter at arms length and at chest level to prevent measuring sound that may be reflected from your body.

In your DAW, insert a pink noise source on a mono track, with the level set at -20bDFS. This will allow you 20 dB of headroom in your mix before clipping occurs. In effect -20 dB is where the average level of your mix will sit. Set your noise generator to RMS rather than peak, so that you obtain an average rather than a peak reading. Set your channel fader at unity gain. First pan the signal to the left speaker. Set the pink noise running, and turn your speaker up or down until you get a meter reading of 79dB at the mix position. Do this for the right speaker, and each of the other speakers (if more than two are used). This should then be your normal “working” level.

It is then a good idea to mark the pot or fader with a marker pen or tape, so that you know exactly where they should be set to always obtain a 79dB reading.

Glossary of Terms used

 

What does dBFS mean?

The term dBFS relates to audio levels. Decibels relative to full scale is often abbreviated as dBFS. This is a logarithmic scale used to measure amplitude in digital systems, which have a defined maximum level before peaking occurs.
The maximum possible digital level is 0 dBFS. Clipping will occur at this point.

What does dBC mean?

The term we are interested in here is dBC or dB(C). Sound Pressure level meters generally have 2 “weighting” response choices.These are dbA and dBC. These relate to the frequency response characteristics of the microphone. An A-weighted setting filters out the low frequencies and emphasises the upper mid frequencies, while a C-weighting curve is a much a flatter one. For the purpose of this calibration, the C-weighted setting is the one used.

Not to be confused with the term dBc which is a telecommunications term and relates to decibels relative to the carrier.

What is Pink Noise?

A pink noise signal contains all the audio frequencies (20 Hz to 20 kHz) distributed equally by the octave within the hearing range of humans. These range from the lowest tones to the highest tones we can hear, and are combined at the same time, and with the same density. Each octave has the same energy , and this means that the power of each higher octave decreases at the rate of 3dB per octave.
The use of limited bandwidth pink noise (500Hz-2kHz) may be a better choice than full range pink noise when using only nearfield monitoring or monitoring that is not full-range.

What is Unity Gain?

Where both the input and output voltage and impedance of a device are at  the same level. This is called  unity gain, and is most commonly marked as “0” on your console or DAW fader.

What is SPL?

 
SPL. A logarithmic measurement of the effective sound pressure of a sound that is relative to a specified reference value. Usually 20micro-pascals at 1kHz is the “zero” reference.The abbreviation SPL stands for sound pressure level. SPL is usually measured at 1 watt and 1 meter in front of a speaker.
 

By Tony Koretz

© copyright 2011. Revised June 2012