Dolby Laboratories 737 - Manual (Page 29)

Model 737 Soundtrack Loudness Meter - Leq(m) Background
A-3
In practice, the following undesirable symptoms have arisen:
• There are an increasing number of audience complaints that movies are too
loud. Newspaper articles have been written on the subject and respected sound
mixers have spoken publicly about the problem.
• Theatres are playing films substantially below the calibrated level. A fader level
of 5, as opposed to the calibrated level of 7, is not uncommon, representing a
level reduction of approximately 6 dB.
• Trailers are fighting for competitive loudness. Theatre playback levels are often
set by complaints generated by the loudest (and earliest) element of the show.
If the playback level is set in response to the loudest trailer, the feature often
plays at the same reduced level. The result is that the dialogue level of the
feature is lowered by the same level deemed necessary to attenuate the trailer.
A feature film played 6 dB below the calibrated level may have serious dialogue
intelligibility problems.
• Mix engineers are using ear plugs to avoid the risk of hearing damage.
• In Europe, where commercials are played before the feature, competitive
loudness has led to the desire for a uniform measurement technique, and a self-
disciplined constraint.
It is possible that the increased use of headroom from Dolby A-type to Dolby SR and
digital releases has not been matched by a corresponding increase in power amplifier
and loudspeaker capability. The resultant distortion from overloaded equipment may
well exacerbate the loudness problems of recent soundtracks, causing increased incidence
of complaints.
A.2 How Loud Is a Movie?
Loudness is an extremely subjective term and has been defined and measured in many
different ways. Various definitions have arisen from a desire to quantify loudness in
specific situations:
• How annoying is the background noise level in a working space?
• How damaging is sustained, high-level noise exposure?
• How intrusive is the noise level of a recording or transmission medium?
• How can the instantaneous loudness of different spectra be compared?
In attempting to measure the loudness of a movie or trailer soundtrack, conventional
level meters in the recording chain are of only marginal help. A VU meter has slow time
constants, and is of little use in detecting short-term peaks. The PPM meter was designed
to show short-term peak levels that might clip the recording or transmission media.
Neither system demonstrates an index of what determines the perceived loudness of a
film soundtrack.
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