Digital Deresonation of Acoustic Recordings

Abstract

Recent research into the problem of eliminating blur and reverberation from digital signals has led to the invention of a statistical deconvolution method based on the theory of homomorphic filtering. The application described here involved the removal of recording horn resonances from old acoustic disks. A major distortion in these disks is the convolution of the recording horn impulse response with the voice waveform. This impulse response is estimated by chopping the recorded signal into many 1-sec intervals and averaging logarithms of the corresponding Fourier transforms. After averaging several such segments, the impulse response emerges in the form of its log Fourier transform and is thereafter removed in a digital convolution involving a computed system inverse. The resulting enhanced sound is generally considered far more acceptable and informative than the original although a slight increase in apparent surface noise is induced. A demonstration will be made. [This research was supported in part by the University of Utah Computer Science Division and by the Advanced Research Projects Agency of the Department of Defense, monitored by Rome Air Development Center, Griffiss, AFB, New York 13440, under contract.]