SHOCK-WAVES IN TROMBONES

Based on physical models of musical instruments and of the human voice , a new generation of sound synthesizers is born: virtual instruments. The models used for wind instruments are simple feedback loops in whi ch a nonlinear sound source drives a linear filter representing the pi pe of the instrument. While very rewarding musical sounds have been ob tained with these models, it has become obvious that some essential ph enomena escape such a description. In particular the brightness of the sound generated by trombones is expected to be due to the essential n onlinearity of the wave propagation in the pipe. At fortissimo levels this leads to shock wave formation observed in our experiments both fr om pressure measurements and flow visualization. A modest modification of the physical model could already take this phenomenon into account . The key idea is that the nonlinear effect is essential for the trans fer of sound from the source toward the listener, but can be ignored i n a model of the generation of the pipe oscillations. (C) 1996 Acousti cal Society of America.