Theatre Catalog (1954-55)

| Basic Principles. of Stereophonic Sound* An Important and Fundamental Study of the Principles of Stereophonic Sound is Offered by A Leading Sound Expert BRIEF: Stereophonic sound has become of vital importance to the industry. The subject has been studied for many years . but the published material is scattered . . . This paper summarizes the fundamental theory underlying stereophonic sound so far as it has been published . . . and gives examples of hou the theory is employed in representative practical situations . . . Fundamental differences between ordinary binaural listening and stereophony are pointed out ... as well as similarities . .. It is shown that much qualitative but little quantitative information has been reported Factors which aid some stereophonic effects are shown to be detrimental to others . . . and methods of minimizing the undersirable conditions are suggested. | SE In 1941 K. de Boer wrote: “When the time comes to make use of stereophonic reproduction in the cinema, in broadcasting, etc., and the opinion becomes more and more general that the improvement in quality so obtained is worth the trouble, it will become necessary in *Most of this article appeared as a paper in the November, 1953 issue of the Journal of the Society of Motion Picture and Television Engineers, and 1s presented with the permission of the SMPTE. 1954-55 THEATRE CATALOG By Witu1aAM SNow Sound Consultant the first place to find a process of making stereophonic records on a large scale.” Although even at that time stereophonic reproduction was far from new, de Boer’s enthusiasm for “making an orchestra plastically audible” was shared by only a few. Now the time he forecast has finally come. Stereophonic sound has suddenly become of vital concern to the motion picture and sound recording industries, with multiplechannel recording the order of the day. Stereophonic reproduction brings a truly remarkable increase in the realism of the sound and in the pleasure of listening to it. In one attempt to measure this quantitatively, reported by Fletcher, the observers listened alternately to single-channel and _ stereophonic reproduction. In the stereophonic channels low-pass filters were inserted, while the single channel was maintained flat to 15 ke. Half of the observers still preferred stereophonic reproductions when the low-pass cutoff was reduced to about 5 ke. However, this paper is concerned primarily with the mechanism of stereophonic sound rather than its advantages, which are now so well recognized. 7 purnees um puigettt t q yea FET mmm pret eee 9 eaten een ee en ean ae G DEFINITIONS As in most. new developments, differences in nomenclature have arisen which tend to obscure precise descriptions of systems. The words “binaural” and “stereophonic” are those most frequently used, but not with uniform meanings. This is not a new phenomenon. Alexander Graham Bell writing in 1880 referred to the ‘“stereophonic phenomena of binaural audition,” in describing experiments on the directional sense in hearing conducted with his newly invented telephone. The following definitions apply to the discussions of this paper, and are limited to electroacoustic sound reproducing systems: Binaural— A system employing two microphones, preferably in an artificial head, two independent amplifying channels, and two independent headphones for each observer. This duplicates normal listening, Stereophonic — A system employing two or more microphones spaced in front of a pickup area, connected by independent amplifying channel to two or more loudspeakers spaced in front of a listening area. This creates the illusion THE ORIGINAL two channel stereophonic sound system is shown in tho foyer of Philadelphia Academy of Music back in the year 1932. — 777 » #2 = ~ a“ ° oe Ve ~ j +) = — 241