Model 737 Soundtrack Loudness Meter - Leq(m) Background
A-4
None of the existing criteria for loudness can be directly applied to a soundtrack.
Fundamental loudness is defined by the relationship between frequency and level. A
regular VU or PPM meter does not account for the ear’s varying sensitivity with respect to
frequency. Sound level meters account for some freq uency/leve l factors and are typ ically
switchable to different weightings. A-weighting, for example, attempts to account for
the ear’s decreased sensitivity to low frequencies.
The length of the sound is another important factor in determining the perceived loudness
of a sound. It is well known that people attending a loud three-hour rock concert may
suffer from some temporary hearing loss after the concert. A five-minute exposure to
the concert, however, does not create the same effect. It can be construed that the longer
a loud sound lasts, the greater the apparent loudness or annoyance. Loud sounds of short
duration may cause great surprise, but little annoyance. A sudden gunshot in the middle
of an otherwise quiet scene causes few, if any, complaints. Repeated gunshots, however,
can distress an audience.
One measure of sustained loudness is called Leq (loudness equivalent), which was
originally derived to gauge potential hearing damage from exposure in industrial
environment s to sustained, varying-level sounds. Leq can be defined as the level of a
steady-state tone with an equivalent level as the level of a time-variant signal. The original
intent was to define potential hearing damage in industrial noise environments. Several
different formulae define Leq, but all perform averaging of the level of material over time.
A.3 Standardizing a Measurement Technique for Soundtrack “Loudness”The following factors must be considered to develop a valid measurement technique:
•frequency weighting – determining the frequency ranges that most closely
correlate to loudness annoyance
•long-term averaging – measurement definitions such as Leq
It would be highly desirable to combine these concepts to produce a single value that
accurately represents the loudness of a movie.
Dolby Laboratories decided to set up a variety of measurement techniques to evaluate
film samples. Obviously, it was impossible to measure a totally comprehensive set of
material. The selected samples used for testing included: contemporary digital trailers,
sections of recent digital releases, maximum level Dolby SR and A-type releases,
typical dialogue-only recordings in various formats (including Academy mono), and
UK commercials.
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