Model 737 Soundtrack Loudness Meter - Leq(m)
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Chapter 1Introduction
Leq(m) is a term used by Dolby Laboratories to describe the level of annoyance in mov-
ie soundtracks. The Leq(m) value is a weighted true average of the audio power level
sent to the camera in optical or digital soundtracks, or the same weighted true average of
the audio power level passing through a cinema processor before equalization. The Dol-
by Model 737 Soundtrack Loudness Meter – Leq(m) provides a convenient method
of measuring soundtrack annoyance.
The phrase true average signifies that the meter measures the power at regular intervals,
adds these quantities together and then divides the result by the length of the measure-
ment time. Since the measurement time is a critical factor in arriving at an accurate re-
sult, the measurement should start and stop at known points. These points can range
from the First Frame of Action (FFOA) and Last Frame of Action (LFOA) of a spot,
such as a ten-second clip, to the beginning and end of an entire movie. The degree of
repeatability of Model 737 measurements is dependent on the length of the measure-
ment. For example, a ten-second spot requires about two frame accuracy whereas a
two-minute-thirty-second trailer needs only two-second accuracy for correct measure-
ment. For an entire feature, the measurement can be started and stopped at a convenient
time, within two minutes of the opening and closing credits, to get repeatable results.
Measurements made within 1% of the stated time frame will compare accurately.
The Model 737 consists of six input channels with setup trims followed by five weight-
ing filters , a true av eraging power meter that can be remotely started and stopped, and a
trip circuit that indicates a preset maximum level has been exceeded. The unit is intended
for use on soundstages, optical recording facilities, and film QA installations to audition
the final two- and six-channel mixes that will be recorded on the film. It can also be
used in theatres to check levels during exhibition.
Note: See Appendix A – Background for a complete discussion of the factors that led
to the creation of the Model 737 Soundtrack Loudness Meter – Leq(m).
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