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Some Photographic Aspects of Sound Recording

1935; Volume: 24; Issue: 4 Linguagem: Inglês

10.5594/j10104

0097-5834

C. E. K. Mees,

Thermography and Photoacoustic Techniques

Since 1928, a very considerable amount of study has been devoted to the photographic problems which arise in connection with recording and reproducing sound. A general understanding has been reached as to the principles involved and as to the conditions which will permit satisfactory quality in the sound reproduced. This lecture represents a summary, therefore, of the general conclusions which have been reached by those interested in the subject. — Sound has three attributes, namely; (1) loudness, (2) frequency or pitch, and (3) wave-form, quality, or timbre. For perfect reproduction of sound, the reproduction should be perfect in respect of all these three attributes. The intensity range is limited primarily by the ground noise, and secondarily by the modulation which is permissible before the wave-form becomes sufficiently distorted to be noticeable to the ear. The ground noise is due primarily to physical defects in the films, such as scratches and dirt, although even in a perfectly clean film there is a very small amount of ground noise due to the granular structure of the silver deposit. This ground noise can be diminished by systems of noise reduction. — The reproduction of high frequencies is dependent upon the resolving power of the photographic film, and the effect of loss of these high frequencies will be illustrated. Special apparatus has been designed for an investigation of the quality of the reproduction, including special sensitometers and densitometers. The analysis of the quality of reproduction and the application of graphic analysis are demonstrated, with an illustration of some of the results attained.