PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Digital cinema: analysis of multi-channel systems to control soundlevelsPeter HOUTAVE1
1

Acoustic Technologies (A-Tech), Belgium

ABSTRACT
Since 2014, Flemish Authorities have installed an auto-regulatory system for cinemas in order to control thesound pressure levels during screening of different digital source materials. In preparation of this regulation,an acoustic study was necessary to fully understand the existing sound pressure levels and how they are
generated in different movie theatres. Therefore, the whole sound system was studied in extensive details to
describe the subsequent steps in the motion-picture multi-channel sound reproduction chains. The analysis
started at the levels [dBFS] of the DCP 5.1 multichannel digital source signals, passing through the signal
processing and amplification, integrating the electro-acoustic and room responses at different listening
positions. As a result, it became clear that in modern digital cinemas with proper room calibration, a goodprediction of the resulting sound pressure levels can be achieved. This result provides therefore a mean ofcontrol of the resulting sound pressure levels even before actual playback. Different sources [film, trailer,
commercial announcement], different sizes of venues and different audience positions were investigated.
Results of the different analysis steps will be presented and discussed.
Keywords: Cinema, Signal, Loudness

1. INTRODUCTION
After having received several complaints about sound pressure levels being too loud in cinemas,
with even a reported case of tinnitus, the Flemish Authorities decided to have an acoustic study ofdigital cinemas carried out. The aim of the study was to gain knowledge concerning the digital cinema
industry and the sound pressure levels for the audience (public) at that time in order to prepare a newlegislation for the hearing protection if it would seem necessary in the light of the obtained results.
The study was conducted in 2012, with final reporting in February 2013. Further work has been
undertaken preparing a new regulation imposing a sound management system for the control of thesound levels in digital cinemas. This system is managed by the cinemas themselves, with obligation tokeep logfiles that can be inspected by the authorities. Since the entry into force of this new regulationin January 2014, the number of complaints has decreased significantly.
The full report being available online since 2013, this paper will emphasize on the discussion of theperformed analyses of the digital loudness and the resulting sound pressure levels in the cinemas.
For readability of the text, sound pressure levels [dB ref. 20 µPa] are referred to as sound levels.

2. SCOPE
2.1 Digital Cinema
The study concerns digital cinema with source material delivered as an DCP (Digital Cinema
Package) of the 5.1 audio channel format. In order to have a good understanding how this works out inpractice, 5 different cinemas were investigated. The selection of those venues targeted different sizes,
with cinema 1 being the largest one with 684 seats and cinema 5 the smallest venue with 96 seats.
Throughout the study, following DCP 5.1 source materials were used: 2 movies, 5 cinematic trailers
and 11 commercials. The first movie is “Ice Age 4 Continental Drift”, where the second movie is “TheExpendables 2”. Movie 1 being intended for children, was played with the Flemish (Dutch) language.
The second movie 2 was played with its original English soundtrack.
1

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2.2 Measurement of Sound Levels Playback
The aim of the authorities was to understand the sound levels that are produced during playback on
different seating positions. Therefore, besides the more averaging measurement positions as used forroom calibration, other positions were chosen in order to assess the risk for potential hearing damage
caused by locally occurring louder sound levels then can be expected in the middle of the seating areas.
In 5 (to 6) positions detailed and synchronized sound measurements were carried out of L Aeq,100ms ,LA,Slow, LC,peak and of Leq,100ms third octave band with central frequency between 12.5 Hz and 22 kHz.
In Figure 1 the fixed positions are shown for measurement during playback of all source material.
SUBWOOFER LFE

LEFT

CENTER

RIGHT

L

C

R

FRONT

1 2 3 4 5 6 7 8 9 10 11 # …
1/3
S1
1
2
1/3 seatings

2/3 seatings

S4

3
4

(S6)

S2 MID

7

RS RIGHT SURROUND

6

RIGHT

5

2/3

LEFT

LS LEFT SURROUND

2/3

8
1/3

1/3

to backseatings

tov
zaal

9

BACK

…

S3
LS LEFT SURROUNDS5

RS RIGHT SURROUNDPROJECTOR

Figure 1 – Principle of distribution of sound level measurement positions over the seating area
Certain positions were specifically chosen being close to or “on axis” of a certain loudspeaker: S1
closest to the subwoofer, S4 on axis of a surround speaker, S3 at the back in the “focus” point of alateral positioned surround speaker and of a surround speaker positioned behind that seat.
Each audio channel of the 5.1 source format has its corresponding loudspeaker(s) in the cinema:
L: left, C: center, R: right, RS: right surround, LS: left surround, LFE: low frequency effect.

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2.3 Measurements Transfer Function
In addition to the previous “fixed” measurement positions during playback of the different “clips”[movies, trailers, commercials], a second series of measurements has been carried out for a double
purpose. First to verify the room calibration for each digital channel [L, C, R, RS, LS, LFE] separately
over the whole audience zone. Secondly to establish the transfer function between each digital channel
and the resulting sound pressure level at the seats distributed over the whole area.
To that purpose, a pink noise of well-known digital loudness [dBFS] was played for 30 seconds
through each of the 6 channels consecutively. Per test sequence, six sound level meters distributed
over the width of a seating row performed the same type of sound pressure measurements as in 2.2.
Between 2 sequences, the 6 sound level meters were placed to the next row. For the two largest venues,
C1 and C2, this was done for each second row. The first and last seating rows were always included.
Figure 2 illustrates the room calibration check in C3 for the digital Left Surround channel with
Dolby Pink Noise played at Main Fader 7 (0 dB gain), and the resulting map of C-weighted noise level.

Figure 2 – Cinema 3: measurement positions and C-weighted noise level map for Dolby pink noise at LS
The transfer functions between each digital channel of the 5.1 system and the sound level at eachmeasurement position were established spectrally with third octave band analysis.
2.4 Calibrated System Setup
In a digital cinema, many parameters of the total electroacoustic chain are well defined. At thesource, the DCP 5.1 of a “clip” contains 6 channels of audio (e.g. 48 kHz, 24 bit) with a digital source
loudness that will not change between cinemas. Secondly, for each digital cinema a room calibration
has been executed. By sending a wide band audio pink noise signal of a well-known digital loudness
through each channel separately, one can perform a calibration of the total gain (processor, equalizer,
amplifier) to obtain an averaged C-weighted sound pressure level [dB ref. 20 µPa] on a set calibration
positions in the venue: L 85, C 85, R 85, RS 82, LS 82 and LFE 85…88 (varies with room size).
The calibration process has also an equalization part to obtain a frequency response curve without
any unacceptable tonal unbalance between different frequencies. Target curves for the frequency
response are also pursued. Depending on the management of the (rooms of the) cinema(-complex),these curves (1) are met with more tolerance because also the subjective sound quality is considered.
An important element in the calibration process, and evenly important during play-back, is the “MF”
Main Fader setting of the cinema-processor. Calibration is performed with the Main Fader at 0 dB gain.
So, after the level calibration (including the equalization) the only gain parameter that can change
before starting playback of an actual clip is that of a global (frequency-independent) volume control,
better known as the Main Fader setting (or position) “MF”.
When discussing sound level measurements, the MF-setting during playback is a key element.

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3. MEASUREMENT RESULTS
During the study many sound level measurements and analyses were performed. In the scope of thispaper some results will be only briefly mentioned. We refer to the report and its appendices (1), where
all detail (time evolution, averages, …) can be found per source material, cinema, seat-position etc.
The key-element during the acquisition of the sound pressure levels in a cinema is the MF-setting
during playback. Whereas the “international industry standard” consists of playing movies at
MF-setting 7 (which corresponds to a gain of 0 dB according the Dolby-curve), actual playback is at alower setting. The main reason is that cinema managers receive complaints from the visitors about tohigh sound levels. This deviation from 0 dB gain however can vary from one cinema to another. Eachcinema manager was asked for his playback MF-settings for the different type of source materials[publicity, trailer, main movie]. The sound level measurements were done with those MF-settings.
Table 1 – Main Fader Settings per cinema for different type of source material
Cinema / Processor

TRAILERPUB

FILM 1 (children)

FILM 2 (action)

C1 / QSC DCP300

-.-

-15.0

-.-

-15.0

-.-

-10.0

-.-

-8.0

C2 / DOLBY CP650

4.0

-12.0

4.0

-12.0

4.0

-12.0

4.5

-8.3

C3 / DATASAT AP20

3.5

-17.5

3.5

-17.5

5.0

-10.0

5.0

-10.0

C4 / DOLBY CP650

3.7

-18.0

3.7

-18.0

4.0

-12.0

3.9

-14.0

C5 / DATASAT AP20

3.5

-17.5

5.0

-10.0

4.5

-12.5

MAIN FADER SETTING [-]GAIN [dB]

In Figure 3, the average LAeq,T over measurement positions S1 to S6 is shown for the 5 cinemas.

LAeq,T [dB ref. 20 µPa]

Average (S1-S6) LAeq,T(Film) measured
85
84
83
82
81
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65

82

FILM1

81

81

FILM2
78
76

74

73

71

71

C1

73

C2

C3*

C4

C5

Cinema (C1-C5)

Figure 3 – Average (S1-S6) of LAeq,T, Film for the 5 cinemas
C3*: Measurement with Main Fader Gain -12.5 dB, Normal operation with Main Fader Gain - 10 dB
The average over 5 cinemas of L Aeq,T,Film1 is 73 dB, and for the second movie LAeq,T,Film2 80 dB.
In the report (1) all results are presented and discussed in detail. The report, the annexes, technicaldetails and information can be found on: https://www.lne.be/geluidszorg-in-bioscopen. Some global
statistics however are interesting when looking at the resulting sound pressure levels in the cinemas forthe assessment of the risk for potential hearing damage. The behavior of LA,Slow,max and LC,peak was very
similar for both movies 1 and 2, considering all positions S1 to S6 over all 5 cinemas. The value of
LA,Slow,max exceeds that of the L Aeq,T,Film with at least 11 dB, but never more than 16 dB. The value ofLC,peak exceeds that of the LAeq,T,Film with at least 30 dB, but never more than 38 dB. Global averaging
yields LA,Slow,max = LAeq,T,Film + 13 dB and LC,peak = LAeq,T,Film + 34 dB. In the annexes (1) all the detailed
analyses [C1-C5, S1-C6, Channels, …] are presented for the movies, the trailers and the commercials.

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4. DIGITAL LOUDNESS AND SOUND LEVELS
4.1 Digital Loudness
The movie source material is delivered as a DCP 5.1 containing 6 channel digital audio. This DCP
remains unaltered between cinemas. So, analyzing the source can yield useful information whenanalyzing the rest of the reproduction chain up to the resulting sound pressure levels in the cinemas.
Different schemes for the calculation of the loudness and other metrics of 5.1 channel clips exist.
The methods are based on the energy summation of the different channels, they can use different
frequency-weightings and the results are expressed in [dBFS] (dB ref. Full digital Scale).
The analyses were digitally performed on the DCP of each clip to calculate the Leq,Tclip [dBFS] toobtain the multi-channel global M-weighted (3), A-weighted and the K-weighted (5) values. The latter
can also be found as LUFS, Loudness Units ref. Full Scale according (6) for as long as the non-gatedintegration method is performed (which is the case in the study and this paper).
The A- and M-weighted values are obtained by summing all channels, but with a gain correction of-3 dB for left and right surround channels to reflect the room calibration for those 2 channels. The
results for the K-weighted values are obtained with the non-gated integration method according ITU-R
BS.1770 and corresponds to the LUFS-value. For LUFS, the LFE-channel is not taken into account anda correction of + ~1.5 dB is applied on the surround channels before summing and a global correctionof -0.691 dB on the over all channels summed value. All W(K)-loudness values correspond to LUFS.
The figure 4 shows the different frequency weightings.

Figure 4 – Frequency weightings – applicable in the digital and/or the acoustic domain
In Table 2 the results of the digital loudness calculation on various clips are shown.
Table 2 – Digital Loudness Analysis performed on the DCP 5.1
TRAILER

MOVIE

1
2
3
4
5S
5L
1
2

W(A)
-21
-21
-22
-22
-20
-21
-27
-20

W(M)
-23
-23
-24
-23
-23
-23
-29
-21
Leq,T [dBFS]

W(K)
-17
-16
-19
-16
-15
-16
-23
-15

PUB

1
2
3
4
5
6
7S
8
9
10
11

W(A)
-21
-23
-22
-24
-24
-25
-21
-21
-21
-21
-18

W(M)
-24
-23
-23
-22
-22
-23
-23
-24
-25
-23
-18
Leq,T [dBFS]

W(K)
-15
-19
-17
-20
-20
-20
-14
-16
-17
-18
-15

Remark: a non-gated integration in the loudness methods, corresponds to the same operation as forthe calculation of the “equivalent value” Leq,T in acoustics.

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During the study there was also an opportunity to perform in a production studio a Leq(M) analysis
on the electric signals with a “hardware” Dolby Loudness meter Type 737 on 2 trailers and 4commercials. The 5 clips produced for 85 Leq(M) dB, yielded in the digital domain W(M) -23 [dBFS].
One clip at 90 Leq(M) dB on the loudness meter, yielded W(M) -18 [dBFS] in the digital domain.
4.2 Main Fader
As discussed above, digital cinemas have a calibrated playback chain. After calibration, the only
factor that will influence - under normal operation conditions not causing any clipping of theamplifiers and in absence of any compressing or limiting - the sound level in the cinema is determinedby the gain set through the Main Fader of the cinema processor (i.e. Linear Time Invariant System).
During the study and discussion with the whole sector (studios, postproduction, cinemas, …) the
Main Fader setting is the common variable in the loudness discussions. According the Dolby Curve,
Main Fader position “7” corresponds to a main gain of 0 dB, at which room calibration is performed.
Playback is in general not done at this level, but at a lower setting. As this is a key element for allparties concerned, the gain-curves of the cinema processors were tested and compared. The QSCprocessor (C1) has no Main Fader “position” but indicates directly the applied main fader gain in dB.
Figure 5 shows the real gain curves as a function of the Main Fader position on the different
processors. All curves pass through 0 dB at MF 7, a zoom is made on fader settings from 3.0 to 5.5.
CINEMA PROCESSOR
Main Fader Setting[ 3.0 - 5.5 ]DATASAT AP20 DOLBY CP650
Dolby Curve
5.5
-7.5
-5.0
-5.0
5.4
-8.0
-5.3
-5.3
5.3
-8.5
-5.6
-5.7
5.2
-9.0
-6.0
-6.0
5.1
-9.5
-6.3
-6.3
5.0
-10.0
-6.6
-6.7
4.9
-10.5
-6.9
-7.0
4.8
-11.0
-7.3
-7.3
4.7
-11.5
-7.6
-7.7
4.6
-12.0
-8.0
-8.0
4.5
-12.5
-8.3
-8.3
4.4
-13.0
-9.0
-8.7
4.3
-13.5
-9.8
-9.0
4.2
-14.0
-10.5
-9.3
4.1
-14.5
-11.3
-9.7
4.0
-15.0
-12.0
-10.0
3.9
-15.5
-14.0
-12.0
3.8
-16.0
-16.0
-14.0
3.7
-16.5
-18.0
-16.0
3.6
-17.0
-20.0
-18.0
3.5
-17.5
-22.0
-20.0
3.4
-18.8
-24.0
-22.0
3.3
-20.1
-26.0
-24.0
3.2
-21.4
-28.0
-26.0
3.1
-22.7
-30.0
-28.0
3.0
-24.0
-32.0
-30.0
[-]

GAIN [dB]DATASAT AP20
3.0

3.5

DOLBY CP650
4.0

4.5

Dolby Curve
5.0

5.5

-5

-10

-15

-20

-25

-30

-35

Figure 5 – Gain as a function of Main Fader Setting on the processors versus theoretical curve
One can see that the actual gain in dB corresponding to the same Main Fader setting on different
cinema-processors can vary significantly. So before discussing the sound levels in a cinema for acertain (new) movie, one should verify that everyone talks about the same (main fader) gain in dB.
This is of the utmost importance for present and future discussions about how to handle loudness incinema, from production stages to the final viewing and listening in the cinemas.
4.3 Measured Sound Levels versus Digital Loudness
In this part, the relationship between the digital loudness and the measured sound pressure LAeq,Tclip
will be discussed. For this operation, all sound level pressure results measured with a MF setting
under 7 are “amplified back” to a (main) gain of 0 dB. So, the actual gain in dB of the processor is usedand not that what the theoretical Dolby Curve indicates for the specific fader position whilst playback.
In Table 3 the measured sound level LAeq,T [dB ref. 20 µPa] averaged over all positions S1-S6, foreach cinema separately and for the average C1-C5 are presented for playback at gain 0 dB (“MF 7”).

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Table 3 – Measured sound levels LAeq,T [dB ref. 20 µPa] for Main Fader Gain 0 [dB] (“MF 7”)

The relationships between the different digital loudness metrics Leq,Tclip [dBFS] as discussed in 4.1,
and the measured sound pressure level L Aeq,Tclip [dB ref. 20 µPa] at Main Gain 0 dB were investigated.
Even though there seems to be some sort of reluctance (in standards, in the community) to use theA-weighting in the digital domain, it was included nevertheless because the aim of this study was tospecifically assess the risk of hearing damage. To that purpose, many limits for exposure during
diverse leisure activities are determined for the A-weighted sound pressure values [dB ref. 20 µPa].
Moreover, having a fully calibrated digital chain at disposal together with in an amplitude and(rather good) in frequency calibrated rooms, this should be an interesting relation to investigate.

94
93
92
91

y = 1.0861x + 111.61
R² = 0.9366

y = 0.8539x + 102.68
R² = 0.7575

y = 0.5297x + 100.15
R² = 0.226

90
89
88
87
86
85
84
83
82
-27 -26 -25 -24 -23 -22 -21 -20 -19 -18 - -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -14 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18(a) A-weighted(b) K-weighted [LUFS](c): M-weighted

Y-axis: Sound level LAeq,T [dB ref. 20 µPa], X-axis: Leq,T Digital Loudness 5.1 CH [dBFS]
Figure 6 – Measured sound levels with main fader at 0 dB gain as a function of digital loudness
When analyzing the relationships, the best correlation +/- 1 dB is obtained with the A-weighted
digital loudness of the source material. The K-weighted digital loudness (= non-gated LUFS) performs
not so good as the A-weighting but accepting the bigger spread +/- 2 dB it remains still a good indicator.
The M-weighted digital loudness has the biggest spread (+2.5 / -4.5 dB) and does not seem appropriate
at all in predicting the sound pressure level LAeq,Tclip [dB ref. 20 µPa] in the cinemas.

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4.4 Controlling the Sound Levels
With the established relationships of Figure 6, two ways of controlling the sound levels are feasible.
Suppose one wants to limit the sound pressure level to LAeq,T,ActionMovie 80 [dB ref. 20 µPa].
For movie 2, with loudness values A-weighted -20 [dBFS] and -15 [LUFS], both predictions givean expected (averaged) LAeq,T 90 [dB ref. 20 µPa]. Setting the main fader gain at -10 dB will do the job.
A second method could consist of a playback at 0 dB main fader gain, corresponding to “MF 7”. To
limit the (averaged) sound levels, the digital source loudness should be controlled. Inverting therelationships, the loudness limits (for any movie) are found: A-weighted -29 [dBFS] and -27 [LUFS].

5. CONCLUSIONS AND FINAL REMARKS
As one of the outcomes of the study, the relation between the digital loudness of the source material
DCP 5.1 and the resulting A-weighted sound pressure levels in 5 cinemas was investigated. With theresults of an extensive measurement campaign during playback, the analysis of the whole digital chain
together with the verification of the room calibration and the check of the real gain in dB as function of
the main fader position, predicting the sound levels is possible once the digital loudness is known.
Although the number of sampled movies is small, together with all the other clips the correlation
between the A-weighted digital loudness and the resulting +/- 1 dB A-weighted sound pressure levels
is very good. The LUFS (non-gated) performs a bit less precise with a +/- 2 dB spread.
The goal is not to discard existing tools and expertise in the management of the (digital) loudness ofmovies, trailers and commercials. However, besides the LUFS loudness one could easily calculate an
A-weighted loudness (with – 3 dB correction for surround channels) in order to have very usefulmeta-data for cinema managers all over the world that are confronted by regulations imposing limits tothe sound levels and/or that just want to avoid customers complaining about too loud sound levels.
During the discussion of the results, no digital loudness target is proposed. The creative process as
such should not suffer (too much) from any sound pressure level control when using all available tools.
More research is necessary to include more movies and cinemas in the datasets. Also, the dynamics
should be further considered. Other loudness metrics exists also: short-term (3 s), momentary (400 ms)
loudness and TPL: true peak level analysis. Further investigations of the relations between the firsttwo and LAeq,1sec,max sound levels, and between TPL and LC,peak sound levels are recommendable.
For the same reason as above, no limit for the LRA loudness range (dynamic) is proposed. Keeping
in mind that many cinema visitors do not like very high sound levels at all (besides potential hearing
damage) and the fact that (other) legal initiatives may be imposed, the industry can only benefit offurther data-collection and the development of new tools with an open mind. This will enable thewhole sector to make their own proposals for the necessary sound level management in cinemas.

ACKNOWLEDGEMENTS
This study was carried out on behalf of the Flemish Government, Department of Environment andSpatial Development. The author wishes also to thank all the participating cinemas, film distributors
and studios for their cooperation during the whole study making all the detailed analyses possible.

REFERENCES
1. Houtave P. Akoestisch Onderzoek in Bioscoopzalen (Acoustic Study in Cinemas), Flemish Government,
Department of Environment and Spatial Development; 2013; Belgium; Available online at link:
https://www.lne.be/geluidszorg-in-bioscopen.
2. ISO 2969, Cinematography - B-chain electro-acoustic response of motion-picture control rooms andindoor theatres - Specifications and measurements; ISO-Standards.
3. ISO 21727, Cinematography - Method of measurement of perceived loudness of motion-picture audio
material; ISO-Standards.
4. ISO 22234, Cinematography - Relative and absolute sound pressure levels for motion-picture
multi-channel sound systems — Measurement methods and levels applicable to analog photographic
film audio, digital photographic film audio and D-cinema audio; ISO-Standards.
5. ITU-R BS.1770-3, Algorithms to measure audio programme loudness and true-peak audio level, 2012.
6. EBU-R 128, Loudness normalization and permitted maximum levels of audio signals, Geneva, 2011.
7. EBU-TECH 3341, Loudness Metering: 'EBU Mode" metering to supplement loudness normalization inaccordance with EBU R 128, Geneva, 2011.

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