A method of and apparatus for analysing a signal is disclosed, the method comprising producing a model of the signal and comparing the model to a predetermined model of a signal due to a phenomenon, thereby to determine whether the model represents a signal due to that phenomenon. A method of and apparatus for detecting the presence of a sample in a larger sample which is not known to contain the sample is also disclosed, the method comprising detecting a signal comprising a response from the sample, producing a model of the signal, and comparing the model to a predetermined model of a response from the sample, thereby to determine whether the sample is present. The techniques have particular application in Magnetic Resonance and Quadrupole Resonance.