Dolby Laboratories 737 - Manual (Page 35)

Model 737 Soundtrack Loudness Meter - Leq(m) Background
A-9
Next, examine Figure A-5 again, then Figure A-6, and compare the peak levels in reel
4 of Shine with the Leq. Although this reel has an extreme dynamic range, audiences
do not complain that it is too loud. In this case, the dynamic range is correct for the nature
of the material, and the Leq is much more indicative of the subjective loudness than a
peak measurement.
Figure A-7 Comparison of Leq(m) with peak levels for UK commercials
Figure A-7 shows that some of the UK commercials are pushing at the maximum
available loudness of the media format. Even these Dolby A-type soundtracks show a
loudness far greater than a constraint on maximum peaks would control. Attempts have
been made in Europe to restrict loudness of commercials by defining a maximum level
with respect to 100% of the medium’s clipping level. For example, a 50% limit would
mean that no peaks would be permitted to exceed a level 6 dB below the maximum
excursion of a Dolby A-type stereo optical release. This constraint, however, would
have the effect of restricting dynamic range, and not necessarily of controlling the
subjective loudness of the material. US-created digital trailers typically have an Leq(m)
level up to 15, or even 20 dB above the feature they advertise!
It must be emphasized, however, that the higher Leq(m) values of trailers is caused, in
part, by the selection of only the loudest, most exciting segments of the movie packed into
the 90-second or two-minute sample. When the entire movie is averaged, the Leq(m)
value is normally much lower.
A.4.1 Verification of the Data
Although the prime measurements for the data were direct electrical sums of the analog
or digital film itself, peak levels were checked periodically with a sound pressure level
meter in an auditorium. The lines indicating Dolby A-type and SR show the maximum
theoretical levels of these formats. The data shows the maximum recorded levels are
slightly higher than these theoretical numbers. This is not surprising and is due to the
slight excessive dimensional modulation consistent with contemporary practice.
A C lip
d u m m ie s
S m irn o ff
7 5
8 0
9 5
8 5
9 0
w a te r
R A F
L e v is
S a n y o
w a tch
d e a th
Leq
m
CCIR-w eighted
Peak Level
C-w eighted, fast
5 .6 d B o ffse t
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