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DUBBING SOUND PICTURES 431
It was found desirable to arrange the amplifiers in the reproducing circuit so as to reduce mechanical vibration to a minimum. Special amplifiers were built to meet the requirements of re-recording work.
It was also necessary to carefully guard against noise being introduced by circulating currents and foreign potentials.
The process of recording is such that there is a tendency for the high frequencies to the relatively under emphasized. This tendency is not objectionable in the original recording, but becomes undesirable in successive recordings, since it is cumulative. Fortunately, it is possible to do almost anything desired with the frequency response of the electrical portion of the system, hence it was only necessary to design an equalizer to counteract the over emphasis of the low frequencies. Due to the variation of different records, the equalizer was made adjustable.
Photographs illustrating dubbed sound tracks are given on Figure 8. The process of dubbing two separate records together is illustrated by track 4, which was produced by combining tracks 3 and 5. The original tracks, 3 and 5, are single frequencies. A re-recording composed of speech and music is illustrated in track 7, being the combination of tracks 6 and 8. From an analysis of track
7, its component parts could be shown to consist of tracks 6 and
8, although with such complex sounds it is not as apparent to the eye as the dubbed track composed of two different sine waves illustrated in track 4. Track number 1 has been combined from two separate records of music and dialogue. This record was then rerecorded four times, track number 2 in the picture being the fifth successive re-recording. It will be noticed that successive re-recordings tend to diminish resolution, which of course affects quality. When the fifth re-recording is projected and the sound compared with the original recording, the quality is not greatly impaired. Such an experiment as this requires the utmost care and supervision, but indicates the possibilities of re-recording. In general, although each re-recording actually introduces a slight loss in quality, in some cases defects in recording, such as "tubbiness" may be artificially improved.
The processes outlined are in a stage of development; consequently the space allotted to this equipment and the type of layouts in the various studios are by no means uniform. It may readily be appreciated that in scoring a picture, the standard recording channel can be used as the pickup by microphone, as in regular picture production, and the mixing is essentially the same. This also holds for the synchronizing operation such as adding sound effects to a completed picture. In the case of re-recording, it is desirable to adjust the volume of the output of the disc and film reproducers so that it may readily be mixed with musical accompaniment and sequences, and thence put through the regular channel. Due to the threefold function of dubbing, it is, of course, desirable to provide for utmost flexibility in the wiring scheme, as indicated to some extent in Figure 7. This, of course, applies to the signaling and motor system, as well as the transmission circuits,