International projectionist (Jan-Dec 1940)

Audience Noise vs. Volume Range CONSTANT research and develop^ merit by sound equipment manufacturers and motion picture studio engineers have resulted in the invention of noise reduction, quieter film stocks, better developing and printing machines, improved photoelectric cells, vacuum tubes, and other items too numerous to mention, each of which has contributed to a reduction of the reproduced noise level of the recording, and therefore an increase in volume range. This fine work has resulted in an overall linear recording system with a greatly extended volume range, and scenes heretofore lifeless and flat can now be presented with greater emotion and realism, and as a consequence have greater dramatic value. The increased dramatic value of the wide-volume-range recordings was quickly realized by the actor and the director, and soon many scenes were being staged to take advantage of it. When pictures recorded with this extended volume range were first released, sound engineers and theatre managers complained that these recordings were hard to understand. This factor of low intelligibility was not noticeable in studio review rooms and was not particularly bad in empty theatres; but in a theatre with an audience present there was considerable dialog that was hard to understand. This was not only true from scene to scene, but was even more disturbing in the loss of intelligibility from word to word. Some words uttered by the characters on the screen could be clearly understood, while others seemed to be absorbed and entirely removed before they reached the audience. In effect, the audience was acting as a selective filter which suppressed certain words and permitted others to pass through to the listener. • Varying Theatre Results This was especialy pronounced at the end of the sentences where many actors have a tendency to lower their voices and trail off into almost inaudible sound. In some theatres it was found that the intelligibility could be improved by raising the normal fader settings; but when this was done the louder sequences in the picture, particularly tj. Soc. Mot. Pict. Eng. (July, 1940). By W. A. MUELLER WARNER BROTHERS' STUDIOS A series of noise measurements were made in theatres to determine the cause of low intelligibility of dialog recordings of wide volume range. Audience noise level was found to be a serious restriction, because it averages 8 db louder than film noise level and reduces the useful volume range by that amount. Audience noise is an extremely variable factor, as measurements made in the same theatre showed it to be o« low as the film noise in one instance and later to rise 14 db above this value. To secure good intelligibility, the volume range of the dialog must be compressed so that the softestspoken words never are so low in level as to be seriously masked by audience noise. the opening title music, overloaded the amplifier equipment. In other words, the amplifier capacity of these theatre equipments was not adequate to reproduce pictures with a wide volume range. In other theatres where adequate power was available, there was considerable audience annoyance because the high-level portion of the dialog became explosive and disagreeable and the actors sounded as if they were '"barking" at one another. The immediate remedy was to raise and lower the sound level manually, effectively reducing the volume range. While this necessary compression of the volume range was in direct contradiction to the premises on which the new recording system had been developed, there was no denying that the manually compressed dialog recordings had higher intelligibility and were less "explosive" than those of wider volume range. Since this loss of intelligibility was not apparent in studio reviewing rooms, and was not definitely pronounced in empty theatres, it must have been due to the theatre audience and was undoubtedly caused by the masking effect of audience noise. That is, the audience noise was sufficiently greater in intensity than certain syllables or words of the dialog so as to make them unintelligible, or even to eliminate them entirely. In other cases, entire scenes and sequences which were spoken very softly were so badly masked by audience noise as to cause complete lack of intelligibility and, consequently, the loss of the story sense of the production. That the aforementioned explanation was true was not apparent even to the most experienced listener, and it was decided to make a series of noise tests to confirm this theory. Table A shows series of noise measurements taken in several theaters and studio review rooms, for this purpose. These measurements were made with a General Radio Type 759 Sound Level Meter, using the weighting networks as indicated. • Representative Readings The figure shown for each theatre represents the average of a large number of readings taken at different positions in the auditorium. Measurements TABLE A. Theatre sound level measurements Theater Venti Audience Quiet lators on Noise Dialog Loud Level Music Huntington Park +28.8 db +30.5 db +43 db +64 db +74 db Granada +23.7 +26.8 +41" +69 +73 Downtown +25.2 +34.5 +43 +66 +74 California +25.6 +29.2 +38 +60 +72 Mission +24.3 +32.4 +44 +65 +72 San Pedro +25.0 +28.3 +40 • +62 +72 Hollywood +24.0 +28.1 +44 +62 +76 Averages +25. 1 db +30.0 db +26 db +42 db +65 db +74 db Studio Review Room No. 4 Studio Review Room No. 5 +24 Zero Power Level = 10" " watt per sq-cm +66 db +65 +76 db +75 14 INTERNATIONAL PROJECTIONIST