A problem encountered when using acoustic shock-waves for kidney stone disintegration is that the positioning of the focus relative to a stone, for the best possible fragmenting effect, is crtitical. The standard methods for focus positioning are ultrasound or x-ray imaging. These methods are, however, not always sufficient and a better indication of a well positioned focus would be valuable. The secondary sound emitted as a result of each shock-wave has been found to contain valuable information. A skilled operator is able to hear from the timbre of these sound pulses when the positioning of the focus is adequate. A method for the automatic evaluation of secondary sounds, using a computer, is developed in this work.