International projectionist (Jan-Dec 1940)

o) the audience noise level were taken when silent trailers were being run or in a silent period between different portions of the show. A silent period of 30 seconds was secured by delaying the start of the next feature, keeping the house lights and the screen dark. It should be noted that the noise level of the empty theatres is quite uniform, averaging +25 db. Also, the noise level is increased to +30 db when the ventilators are turned on. The noise caused by the audience, however, is surprisingly high, averaging + 42 db and masking all other types of noise! Audience noise also is subject to a wide vibration, rising to as high as + 48 db at the end of the main feature when many people were leaving and entering. A measurement of +32 db was also obtained during a very dramatic sequence when the audience was unusually quiet. The figure of +42 db was the average of many such readings. The average level for dialog was +65 db, and loud music reached a level of + 74 db. The loud music consisted of opening and closing title music and musical numbers, which are the loudest portions of any sound film and are recorded at 100 per cent modulation. These measurements show that a range of only 32 db is available between the loudest music reproduced in these theatres and the level of the audience noise. It has been found that the dialog should be at least 6 db above any noise level in order to be clearly understood. This requirement would mean that the absolute minimum level of the dialog should be +48 db. Since the maximum level in the auditorium which is attained at 100 per cent modu lation of the film was +74 db, the usable volume range remaining is only 26 db. • Lowest Permissible Level This means that dialog which can be clearly understood in a theatre must never fall more than 26 db below 100 per cent modulation of the recording medium, as any words or scenes which fall below this level will be masked by audience noise and not understood. The only way that this permissible volume range for dialog can be increased is to reduce the noise level in the theatre, or to increase the maximum loudness that can be tolerated on dialog. The audience noise level is very difficult to control and since psychological and physiological factors determine the annoyance caused by loud sounds, it appears that there is no easy way to extend this volume range. Inspection of Table I shows also why the intelligibility of the high-volumerange recordings was not impaired in the studio review rooms where, without an audience, the noise level is at least 15 db below that of the average theatre. This results in a usable volume range of 40 db, permitting the low-level syllables, words, or scenes, which are lost in a theatre, to be clearly understood. Several pictures were recorded and released with dialog of reduced volume range, based on the aforementioned analysis (see Table I), and excellent results were immediately obtained. Complaints on lack of intelligibility ceased, and the reports showed that cueing of the sound level of these pictures, in the theatres, was no longer necessary or being practiced. As a result the pro 0 \ \ fe * <o 0 ^ ^ <--r7S 7^Ta.c fv7i*KS*c, $**oi/r/*?G, § 4 £jcA:>*.o-S'Of*&, /E~t-c. -+/o ("/OO^t /Wo<ots*-'*sr,o'^) >l -+65 A^£-*?*X&£ <^ALOO^C ^ &ck*: ^<rvfft i Vl -+60 M + Sf 8 § -+JO /VZ/fV/iW^yw i £3 /*+.*. a&Lt£ L ex*. 8 -±■45 V -±■40 7+*CAT*9C A/Off* ££*££. VI • * 1 -+3S f**-A*4 SVo'tr Lr^sA. -+JO s -+2} —UB. FIGURE 1 Volume characteristics of Warner Brothers' recordings cedure was adopted universally for all Warner Bros.' releases, and at present the volume range of the dialog in our pictures is limited to 25 db. This restriction of volume range is secured by means of electronic compressers which are installed in all recording channels. While it has been found impossible to use the full volume range of the recording system for dialog because of audience noise, the present dialog recordings are still of greater range than those formerly released, and many fine comments on their naturalness and dramatic qualities have been received. • Various Relationships It should be emphasized that only the volume range of dialog has been under consideration, and our conclusion is that there should not be more than 25 db difference between the softest whisper and the loudest spoken word. The relation between the loudness of average dialog and opening or closing title music or musical numbers, has not been discussed, but our measurements show that for Warner Bros.' pictures it averages about 9 db (see Fig. 1). The producers and studio executives would like this figure increased ; but so many complaints are received that the music is too loud whenever this is done, that a compromise has been made on the above figure. Many of these complaints come from exhibitors with old or obsolete sound equipment, which overloads on the high-level passages. Until these equipments are replaced, the dramatic effect desired by the producers can not be put into motion pictures. There is also another serious Hmitation to the most dramatic use of sound in motion pictures, and that is because even our present recording systems do not have sufficient volume range to accommodate loud explosions, battle scenes, earthquakes, and so on. Many theatres with modern equipment cue these scenes by raising the level as much as 10 or 12 db, resulting in a much more dramatic and effective presentation. In order to accommodate these sounds the level difference between normal dialog and 100 per cent modulation should be increased from 9 db to 20 db. The acoustic level of the loudest sounds could then rise to +84 db instead of +74 db as at present. The sounds which would rise to this level would be sound effects only, as experience shows that audiences object strenuously to music which rises even 2 or 3 db above the loudness of present title music, i.e., +74 db, as meas(Continued on page 23) AUGUST 1940 15