Initial Characteristics of Impulse Response for Real and Artificial Reverberation

Abstract

Studies by Schroeder et al. [J. Acoust. Soc. Am. 33, 1061 (1961); J. Aud. Eng. Soc. 9, 192 (1961)] have shown that artificial reverberation can be made both colorless and flutter-free, using computer-simulation techniques. However, for economic reasons, commercially available reverberators only approximate these desirable attributes of real reverberation, and yet are satisfactory for many sounds. Several types of reverberators have been obtained and the initial impulse response investigated and compared with that of actual enclosures. It has been found that artificial reverberation produced by these devices generally exhibits an audible pulsing action (flutter) during the first part of the reverberation process, which can be correlated with oscillograms of the impulse response. The first echo usually occurs somewhere between 15 and 50 msec after the originating pulse (direct signal). The pulse density during the immediately following period (say, 500 msec) is relatively sparse, but may build up during the remainder of the reverberation process if multiple-mode transmission occurs. In the case of real reverberation, a high-pulse density is obtained much earlier depending upon the volume of the enclosure and the positions of the microphone and sound source. The initial reverberation characteristics of devices using helical springs, tape delay, or a steel plate are compared with an auditorium, a church, and computer-generated colorless reverberation.