Physical Factors* 



By J. C. STEINBERG and W. B. SNOW 



In considering the physical factors affecting it, auditory perspective is 

 defined in this paper as being reproduction which preserves the spatial rela- 

 tionships of the original sounds. Ideally, this would require an infinite 

 number of separate microphone-to-speaker channels; practically, it is shown 

 that good auditory perspective can be obtained with only 2 or 3 channels. 



ABILITY to localize the direction, and to form some judgment of 

 the distance from a sound source under ordinary conditions of 

 listening, are matters of common experience. Because of this faculty 

 an audience, when listening directly to an orchestral production, senses 

 the spatial relations of the instruments of the orchestra. This spatial 

 character of the sounds gives to the music a sense of depth and of 

 extensiveness, and for perfect reproduction should be preserved. In 

 other words, the sounds should be reproduced in true auditory per- 

 spective. 



In the ordinary methods of reproduction, where only a single loud 

 speaking system is used, the spatial character of the original sound is 

 imperfectly preserved. Some of the depth properties of the original 

 sound may be conveyed by such a system, ^ but the directional proper- 

 ties are lost because the audience tends to localize the sound as coming 

 from the direction of a single source, the loud speaker. Ideally, there 

 are two ways of reproducing sounds in true auditory perspective. One 

 is binaural reproduction which aims to reproduce in a distant listener's 

 ears, by means of head receivers, exact copies of the sound vibrations 

 that would exist in his ears if he were listening directly. The other 

 method, which was described in the first paper of this series, uses loud 

 speakers and aims to reproduce in a distant hall an exact copy of the 

 pattern of sound vibration that exists in the original hall. In the 

 limit, an infinite number of microphones and loud speakers of infin- 

 itesimal dimensions would be needed. 



Far less ideal arrangements, consisting of as few as two microphone- 

 loudspeaker sets, have been found to give good auditory perspective. 

 Hence, it is not necessary to reproduce in the distant hall an exact 

 copy of the vibrations existing in the original hall. What physical 



* Second paper in the Symposium on Wire Transmission of Symphonic Music 

 and Its Reproduction in Auditory Perspective. Presented at Winter Convention of 

 A. I. E. E., New York City, Jan. 23-26, 1934. Published in FJeclrical Eni^ineering, 

 January, 1934. 



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