RECORDING AND REPRODUCING OF MUSIC AND SPEECH 49!^ 



ing the ears of an imaginary listener to the original performance would 

 have had. Obviously, it is very difficult, if not impossible, to fulfill all 

 of these requirements with a single channel system, that is, with a sys- 

 tem which does not have a separate path to each ear of the listener from 

 the sound source. 



The use of two ears, that is, two-channel listening, gives the listener 

 a sense of direction for each of the various sources of sound to which at 

 a given moment he may be listening, and, therefore, he apprehends 

 them in their relative distribution in space. It has been found possible 

 with a single channel system, however, by controlling the acoustic 

 properties of the room in which the sound is being recorded, to simulate 

 to a considerable degree in the reproduced music the effective space 

 relationships of the original. In this case, with a one-channel system, 

 the directional effect is, of course, entirely absent, and the spatial rela- 

 tionship which is apprehended is probably due to the increased appar- 

 ent reverberation of the instruments situated at the far end of the room 

 as compared with those in the near foreground. 



In recording work, therefore, one of the important acoustic charac- 

 teristics of a room is its time of reverberation. Although it is probable 

 that this is the most comprehensive single factor, experiment has shown 

 that the shape of the room and the distribution and character of the 

 damping surfaces play a part in the excellence of music in such a room . 



It has been shown by Sabine^ that for piano music, studios should 

 have a time of reverberation measured by his method of 1.08 seconds. 

 Experience has indicated that this figure is also very closely correct for 

 other types of music. This figure of Sabine's assumes binaural listen- 

 ing. With single-channel systems, such as most of the present repro- 

 duction systems, whether for radio or the phonograph, the ability of 

 the listener to separate the reverberation from the direct music by 

 means of the sense of direction is completely removed and there is 

 thrust upon his attention an apparently excessive amount of room echo. 

 Experiment has shown that a time of reverberation for the recording 

 room ranging from slightly more than 3^ to slightly less than ^ of 

 Sabine's figure affords in the reproduced music the effect of a room with 

 proper acoustics. When this effect is accomplished, the person listening 

 to the reproduced music has the consciousness of the music being 

 played in a continuation of the same room in which he is listening and 

 also has a sense of spatial depth. 



Experiment has indicated further that any transients set up by the 

 recording or reproducing system constitute a second cause of apparent 



^ Collected papers of W. Sabine. 



