Modeling Small Room Responses with a Real-Time Digital Filter

Abstract

A real-time digital filter system designed for speech processing [D. A. Berkley and T. B. Batemen, Int. Congr. Acoust., Budapest (1971)] has been used to model the response of several small rooms. Finite impulse-response filters corresponding to room transfer-function magnitude and phase were synthesized using (1) frequency sampling [L. R. Rabiner and R. W. Schafer, IEEE Trans. Audio Electroacoust. 19, 200 (1971)] realized with parallel second-order filter sections and (2) time domain design implemented in direct form. Both allow approximately 20 msec of the response in a 3-kHz bandwidth to be modeled in real time. In principle, any response can be modeled using this system by overlap processing (non-real time). Using the real-time filter, we have studied the effects of modifying the spectral and temporal properties of the room impulse response (see Berkley et al., Paper F8). Both design methods work but noise considerations rapidly become important when using frequency sampling. [Some aspects of this paper were orally presented at the 1972 International Conference on Communications, Philadelphia.]