EFFECT OF MODULATED DELAY TIME OF REFLECTION ON AUTOCORRELATION FUNCTION AND PERCEPTION OF ECHO

An indoor sound field can be regarded more or less as a time-variant system. In this paper, the time-variant model of the impulse response, which consists of a direct sound and a reflection with a modulated delay time, is applied to simulate such a time-variant sound field. The effects of the modulated delay time of reflection are investigated in terms of physical properties and subjective evaluation of the temporal fluctuation of a sound field. The physical properties of the temporal fluctuation are analyzed by using the autocorrelation function (ACF) of the sound field and identified by the factors and behavior of the ACF. To examine subjective evaluation of the temporal fluctuation of a sound field, listening tests on the perception of echo were conducted. Such subjective evaluation may be associated with the ACF of a sound field. The relationship between the physical properties and the subjective evaluation of the temporal fluctuation of a sound field is also discussed.