Dolby Laboratories 737 A.4.1 Verification of the Data

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 th e 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 Clip

dummies

Smirnoff 75

water

RAF

Levis

Sanyo

watch

death

5.6 dB offset

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