Artificial reverberation

Abstract

The demand for a source of artificial reverberation in sound transmission systems is commonly met by the use of reverberation rooms, but attempts have been made to fulfil the requirements by devices involving the transmission of the signal through a number of delay channels. The design and operation of such devices can be treated by simple theory, but in the present state of the art, the quality of artificial reverberation, like that of the natural product, cannot be completely assessed except by ear.The characteristics of artificial-reverberation apparatus employing delay channels with overall feedback are discussed and illustrated by the results of early experiments using acoustic-delay tubes. The acoustic-tube system, while simple in principle, involves in practice much instrumental complication and becomes uneconomic if good sound quality and long reverberation time are required.Artificial-reverberation apparatus employing a magnetic-recording delay system, which is free from the defects associated with the acoustic tube, is described. By means of an artifice involving the use of a double recording track, the effective number of delay paths is greatly increased and a high standard of performance is thus attained. This equipment has been in regular use by the B.B.C. for 2½ years.Artificial-reverberation systems involving a finite number of delay paths tend to produce flutter effects when transmitting impulsive signals. Such effects can be mitigated by the use of a small auxiliary reverberation chamber. By temporarily transferring the signal to the ultrasonic-frequency region, the required effect can be conveniently obtained with a small water-filled reverberation tank. Details are given of equipment of this type which has been designed for use in conjunction with the magnetic recording system referred to.