Journal of the Society of Motion Picture Engineers (1930-1949)

considerably different from the normal usage of this word. In accepted sound practice the reproduction objective is to bring the sound source into the presence of the listener. Listening to a binaural recording can best be described as literally taking the listener into the presence of the scene where the original recording was made. This effect of realism is particularly effective when listening with headphones. When considering theoretical factors it would not seem that loudspeaker listening would be very effective for binuaral reproduction. However, listening tests readily convince one that considerable enhancement is still retained with speakers although not of such a high order as that of earphone listening. The use of earphones prevents a listener from turning his head to aid in localizing sound sources; loudspeaker reproduction on the other hand allows a listener to retain this mechanical aid to localization. Loudspeaker placement is of considerable importance in good reproduction. The use of too large or too "live" a room or too great a listener distance greatly reduces the effectiveness of binaural loudspeaker reproduction. Random Noise Correlation An unexpected effect was noted when some rather poor recordings were unintentionally made and then played back. When the recording medium or equipment random-noise level is high with respect to the level of the recorded signal a unique result ensues. The random nature of this white noise is such that it allows false phase and amplitude coincidence to be correlated by the brain to produce apparently localized sources of noise. The localization means focused listening attention; the effect thus results in raising of apparent loudness of discreet noise "pulses." Since these pulses are strictly random mental correlations, their number is far less than the actual number of white noise "pulses"; therefore, the net effect is a coarsening and apparent increase of the background noise level to the listener. Practically speaking, this means that binaural recordings made for maximum music appreciation should be made with particular care toward maintaining the best overall measured signal-to-noise ratio. The Tape Transport The development of the binaural tape transport from a standard recorder was very desirable in order to keep manufacturing costs down and allow sales at a reasonable price to the customer without the necessity for designing a new special unit with its attendant reflected high sales price. It was found possible to extend the development of a standard Magnecord PT63-A tape transport mechanism for use in a binaural recording system. This basic tape transport mechanism possesses an assembly incorporating three heads. The tape passes in succession over, first, the erase head, then, the normal recording head, and, thence, over the tape monitor head before it is pulled by the capstan and fed to the take-up reel. Consideration was given to the possibility of retaining the tape monitor feature for the binaural system. However, it was determined that the additional system complexity would add materially to equipment size and costs because of the immediate requirement for two monitor heads and two amplifier monitoring channels as well as extra controls. The mechanical layout of the front panel of the existing PT63-A tape transport unit would also be unduly complicated by the addition of the two extra magnetic heads required. It was, therefore, decided that the normal full-track record head would be replaced by a half-track record head and the position normally occupied by the monitor head would be used for a second half-track record head for the other half of the tape. 112 August 1952 Journal of the SMPTE Vol. 59