Monitoring of machining processes by the use of acoustic emission (AE) is a common technique. But the relation between the measured AE signal and the machining process is often not obvious. Here we present a method for the determination of the transfer function of the complete signal path between AE source and monitoring device. The signal acquisition system including the AE sensor can thus be “calibrated”, which allows the scaling of the measured signal in physically interpretable units. The method is specially adapted to the situation found in monitoring of machining, where the sensor position is fixed and the signal path is therefore kept constant.