The diagnostic investigations of rotating machinery in varying conditions of its operation make it possible to observe machine responses on different excitations. The vibration signals are effects of phenomena related or not related to the variability of the machine operation conditions. The time-frequency methods of analysis of vibration signals enable us to detect signal components and their variability in the time. The time-frequency characteristics allow visual estimation of signal components, which are connected and not connected with the changes of machine operation. Most of these components are symptoms of some phenomena occurring during object action. These phenomena might be related to the changes of machine properties (eg. resonance properties) as well as they may be related to the environmental or operation conditions of the machine. It should be stressed that these characteristics are very often out of use in automatic diagnostic systems. In this case identified symptoms should be separated and first of all they must be described in proper manner. It can be solved by many ways. The paper deals with the description of the machine operation in the varying conditions with the use of dynamic scene idea.
