International photographer (Jan-Dec 1934)

. Ipril, 1934 The INTERNATIONAL PHOTO G R A P II E R / wenty-ouc then make any minor changes in the arrangement necessary to provide the most satisfactory musical halance, hecause the exact distribution of the instruments depends largely on the playing of the individual musicians and on the musical director. Once the positions of the musicians and the microphones have been adjusted to the proper sound system, the lower the ground noise level; although there is a certain point beyond which it is physically impossible to advance. Overloading (louses Distortion The overload point is defined as the point at w hich the recording device (the light valve in the Western Ele< Mike set up location shooting Olympic Stadium. Monitor man and directors discussing coming shot. relationship and the hard and soft screens have been set in place there is no need for changes during the recording. The arranging of the orchestra and the locating of the microphone are much more critical when a single microphone is employed ; but some monitor men claim that it is worth the extra effort because the recording obtained seems more "unified". That assumption, however, is debatable. The author personally prefers three microphones for scoring music and one microphone for recording dialogue. Regulating the Recording Level Control of the recorded music is provided by the three mixer controls associated with the three microphones. If the brass-winds predominate and the stringed instruments can barely be heard in the monitor horns, the output of the microphone before the brass-winds is turned down and the output of the microphone before the stringed instruments is raised until a harmonious blend of the various instruments has been obtained. The overall volume supplied to the recording system during scoring is regulated by the main volume control, the mixer controls being left set. Volume Range of Recording Systems Whether recording music or dialogue, the monitor man has another important thing to watch besides the placing of the microphone: he must not permit the volume of the recorded sound to vary beyond the electrical limits of the recording system. These limits of the recording system are defined by the ground noise level at the lower end of the recording range and by the overload point at the upper end of the range. Ground noise is inherent in every sound recording or reproducing system. It is produced by such tiny extraneous noises as the breathing of the persons on the sound stage, the faint rush of the ventilator system, and noises in the microphone. The hiss of tubes in the amplifiers, noisy resistors, electrical leakage, and battery noise all add their minute quota to the ground noise. Allowance must be made for the additional ground noise that is introduced by noises in the reproducing system when the sound record is reproduced — such as the noise generated in the pick-up unit by dirt on the film sound track or roughness in the wax record ("needle scratch"), and sound in the theatre produced by the shuffle of feet and the coughing of the audience. The better the Courtesy Paramount Photo shows the wall construction that causes much trouble with vibration and emphasis of certain frequencies. trie s\stem) or the recording amplifiers overload and cause harmonics and distortion to be present in the sound record. The recording system will handle an electric current of just such a maximal value, and when that value is exceeded the system is overloaded, just as a tank will hold just so much water without overflowing and no more. If the monitor man attempts to record a sound that is below the ground noise level, such as a low whisper, the ground noise — both in the recording and reproducing systems— will completely obliterate it and make it impossible to distinguish the sound when it is reproduced. If the intensity of a sound is too great to be recorded1 — a gunshot for example — and the monitor man does not turn his mixer controls down far enough to cause a sufficient reduction in its intensity, the sound will be recorded at such a high level that it will cause the light valve to clash or exceed the carrying capacity of the amplifiers. Ideal Sensitivity Range The maximum intensity range of the normal human ear under ideal conditions in the open is approximately 130 decibels (a term which wall be explained in a later chapter) at a frequency of 1024 double vibrations per second. This value may be checked by the reader by referring to the composite acoustic chart printed with Chapter III in the November issue, remembering that sensation units correspond to decibels. Incidentally, the greatest range of sensitivity of the human ear is at this frequency, decreasing with higher or lower frequencies. A high-grade recording system operated under ideal conditions in the laboratory as a sensitivity range of approximately sixty decibels ; although under actual studio operating conditions its range is considerably less, due chiefly to the amount of extraneous noise always present in a sound stage during production. The seriousness of this discrepancy, however, in the sound volume ranges of the present recording systems and the human ear is not as great as might at first seem. Natural Limitations of Range The ground noise that is inherent in both the recording and reproducing systems and the continual crowd noise that forms a faint under-current of sound in a theatre combine to raise the level of minimal audibility required of a sound system to a point about thirty decibels above the absolute minimal value given for the human (Turn to Page 28) Please mention The International Photographer when corresponding with advertisers.