Particle-impeller and particle-well collision sounds in a stirred tank were shown to be distinguishable by wavelet analysis. The influence on the collision frequencies of operational conditions such as rotational speed, particle size and concentration, was examined based on a method developed in this study. once collisions became detectable at the respective critical rotational speed, termed the critical particle collision speed, the frequency of impeller collisions was found to increase linearly with impeller speed while that of wall collisions increased exponentially. Both collisions frequencies increase a with particle size in the examined range, but particle concentration had little effect on the frequencies. In addition, the intervals between collisions with the impeller were found to show a log-normal distribution independently of experimental conditions, while those with the wall showed a decay distribution, since extremely short intervals were not observed.