In stereophonic reproduction there are two distinct qualities which distinguish it from single‐channel reproduction. The first of these is a directional separation of sound sources and the second, and probably the most important characteristic of stereophonic reproduction, is the sensation of “depth” and “presence” that it creates.

It is well known that the relative amplitudes and times of arrival at an observer's ears of first sounds received from the loudspeakers determine the apparent direction of the sound sources in a stereophonic system, and it is often assumed that this is also responsible for the perception of “depth” and “presence” normally linked with this system. It appears, however, that only the former quality, directional separation, is based on the relative amplitudes and times of arrival of first sounds and that the latter quality, which we call “ambience,” is entirely on account of delayed reflections or echoes recorded and reproduced through the separate channels of the stereophonic system.

Single recording‐channel quasi‐stereophonic systems, in which these echoes were brought out as in the stereophonic system, but which could not give separation of sources, were subjectively compared with true stereophonic systems and the results are presented in this paper.

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