This paper describes a convenient PC-based acoustic signal processing system and its application for monitoring hydrocyclone performance. Acoustic emissions generated from a five inch diameter hydrocyclone under different operating conditions were collected using a single 190 KHz passive acoustic sensor mounted externally an the conical section of the hydrocyclone. Subsequent analysis shows that the spectral characteristics of the signal are sensitive to the variations of operating parameters (feed pressure, solid concentrations, mass and volume flowrate and underflow solid concentrations). Use of multivariate statistical analysis techniques allows the quantitative relationships between various operating parameters of the hydrocyclone and the statistical and spectral characteristics of the acoustic signals to be established. The application of this sensor technology to audit classifiers and its potential for real-time control is demonstrated based on a laboratory case study.