Continuing development of process analytical technology (PAT) tools is needed in the pharmaceutical industry to provide more flexible processing and achieve products of consistent quality. For high-shear wet granulation, audible acoustic emissions (AAEs) have shown potential as a PAT tool for monitoring changes in physical properties related to product quality. This article develops the relationship between AAEs and two critical quality attributes, size and density, and investigates the potential for monitoring product quality online. Condenser microphones were placed inside the air exhaust of a PMA-10 high-shear granulator to collect AAEs for a design of experiment (DOE) where particle size and density were varied by changing the grade of Avicel in the formulation. The results showed increases in particle size and density affect the observed decreases in the AAEs at granulation end-point and during over wetting. In addition, the changes in size and density could be represented by different combinations of 10 Hz frequency groups and the trends in the multivariate scores support online monitoring. (C) 2011 Elsevier B.V. All rights reserved.