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1954-55 Theatre Catalog, 12th Edition, Page 281 (245)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 281
Page 281

1954-55 Theatre Catalog, 12th Edition, Page 281

demanded by motion picture and auditorium reproduction its use appears questionable until a great deal more study of it has been reported. The Philips test employed microphones a small distance apart; with widely spaced microphones characterizing the practice in this country, serious pickup dithculties can be foreseen, as well as itcrossoverd complications in the loudspeaker systems, For "special effects loudspeakers" however, the low frequencies do not appear necessary if the main object is to obtain localization.

Arrival-Time Difference

Another phenomenon affecting angular localization is the change in arrival time of the direct-sound pulses from the several loudspeakers as the source moves upon the stage. These differences were mentioned above, and were shown to be considerably greater than those ordinarly encountered in simple binaural hearing. For example, in Figure 2 the right and left channels reproduce sound pulses from the source later than the center channel by time intervals corres ponding to distances a and b respec tively, The observer does not recognize the three pulses as distinct. However, it has been shown, that localization tends towards the loudspeaker which reproduces the earliest pulse. These effects have been called ttFusion" and the "Precedence Effect" by Wallach, Newman, and Rosenzweig. Qualitativer their discussion applies to stereophonic reproduction in general, but the precise data on precedence is limited to time differences of 2 msec or less, whereas common stereophonic conditions produce differences much greater than this. The following qualitative statements are deduced from this writers own experi ence: K at


(a) The effect of arrival time is to make localization tend toward the loudspeaker from which the pulse arrives first.

(b) This effect is strong for small differences, say up to 3 or 4 msec, and tends to become weaker for greater time differences.

(c) The effect is relatively independent of where the diiferences are produced, whether on the pickup stage, in the listening room, or in the reproducing channels. Therefore differences in one section add to those in another, or can be made to compensate each other.

(d) These effects can be largely compensated by intensity or quality differences inserted in the channels, for any one observing position.

This effect acts to reinforce the intensity effect for movement on the pickup stage. As a source moves toward a microphone the arrival time is advanced at the same time that intensity is increased. This is one of the important factors not duplicated by the bridged system. An interesting application is described by Grignon in the triangular microphone arrangement for assuring center localization while maintaining stereophonic quality for a soloist or small source. Here the small advance of arrival time on the center microphone holds localization to the corresponding loudspeaker.


A fourth factor that might contribute to angular localization is ratio of direct to reverberant sound. Experience has shown, however, that it plays a very minor part in angular localization.

BINAURAL system employing two microphones in dummy head. connected individually to an earphone ior each ear used in 1932 experiments.

Dynamic Localization

Moir and Leslie provide a very interesting observation on localization, as follows: 't. . . dynamic localization of a source appears to be appreciably more accurate than is shown by the data obtained from localization tests on a stationary source. This applies to all variations of two and three channel systems that we have compared."

Depth Perception

Depth perception in stereophonic reproduction is controlled by essentially the same factors as in ordinary binaural listening described above, viz: absolute intensity, quality, and ratio of direct to reverberant sound. As the sound intensity decreases, thelimpression is produced of the sound moving away. The same illusion accompanies a relative loss of high frequencies. The most important contributor to the feeling of depth, however, is change in the ratio of direct to reverberant sound on the pickup stage. As the reverberant energy becomes more prominent, the source appears to recede 0n the virtual stage. In practice the microphones are closer to the sound sources than listeners would be, and changes in direct-toreverberant sound ratio can be heightened to give more definite impressions of depth on a virtual stage than are created on a real stage. As in ordinary listening, however, depth localization is less precise than angular localization.

Effect of Observer Position

Up to this point for the sake of simplicity, the paper has been written as if all observing positions were equally good. Actually this is far from the case, as all experimenters have pointed out. From the standpoint of the practical use of stereophonic reproduction in thea

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1954-55 Theatre Catalog, 12th Edition, Page 281