Volume Distortion

The contention that a linear recording and reproducing system represents the ideal, and that sound handled by such a system will be exactly represented, is not borne out by experience. Systems have been built which meet this requirement within limits that are not detectable by the ear and yet these systems do not reproduce sound as it actually is produced. In many cases a definite non-linear response curve is provided to compensate for some factor that is not covered by the above contention. It is the author's thesis that this discrepancy is due to the ear sensitivity to frequencies as a function of loudness. — Using the ear-sensitivity curves presented by Fletcher and Munson of the Bell Telephone Laboratories (which have been verified by other observers) it is shown how the ear introduces frequency distortion to a linear system when the sound is reproduced at a level other than the level at which it is produced. It is shown how a sound reproduced above the incident sound-level introduces excessive low frequencies. The case for a sound reproduced at a lower level is also examined and the conclusion is drawn that this case accentuates the high frequencies. — It is further shown that the possibility of correcting for the limited volume range of all sound systems may lie in the type of amplifier response curve. — A description is given of three methods used to achieve the desired amplifier characteristics: (1) a mechanical method, (2) a linear-non-linear system, and (3) a selective by-pass system. Circuits are given and the important operating points of each are discussed. The objections to each system are also given. — Further, a brief summary, with diagrams, describes the various set-ups used to record with these amplifiers. This covers work for radio, disk record, and sound-film.

Print ISSN

0097-5834

Published

1940-01

Content type

Original Research

DOI

10.5594/J00026