Spectral analysis is a very common tool in vibration monitoring. While useful in machine diagnostics, spectral analysis can be rather time consuming. Tasks that require an extensive amount of time are often considered too expensive, especially in modern industry. To achieve an automatic monitoring system of some kind, different features, such as the root mean square (RMS) or the peak value of signals, are often monitored. These are special cases of generalised norms, which can be effective tools to determine whether a signal has shown some kind of change and how notable the change is when compared to a previously measured signal, for example. However, no spectral information is obtained in this way and the question regarding the frequency in the signal at which the change has occurred remains unanswered. Generalised spectral norms are a frequency-domain application of these norms and, as presented in this paper, provide a suitable way to perform automatic monitoring regarding the spectral information, for example.