Real-time wave separation in a cylindrical pipe with applications to reflectometry and echo-cancellation
Jean Guérard, Xavier Boutillon · The Journal of the Acoustical Society of America · 1998
Precise control of the acoustical pressure all along a pipe requires that backward and forward propagating waves are separated in real time. This has been achieved by means of an array of up to five microphones, a high-precision analog calculation, and a real-time numerical post-treatment. The separation factor exceeds 40 dB over several kHz, when special attention to intercalibration issues and to the realization of the analog part is given. The theoretical limit at high frequencies has been reached experimentally. The advantage of a partial analog treatment over a fully numerical one will be discussed. One application consists in reflectometry (and consequently, impedancemetry) without use of the long pipe normally required. Associated with a real-time DSP processor (TMS 320C30), wave separation also permits one to efficiently control the wave reflected by one end. This is done with only one loudspeaker, whose transfer function has been inverted and implemented in the DSP as an IIR filter. This approach of active-control differs from adaptative procedures. Finally, a musical application of the system to a hybrid wind instrument will be presented. [Work supported in part by the French Ministry of Culture.]