A method for analysing signals received from an object. The method initially comprises deriving the parameters of frequency and phase of said signals in either the time domain or frequency domain. It then comprises identifying whether the signals conform to a linear relationship between the two parameters to ascertain whether a true signal representative of a character of the object is present. The character may be a nuclear or electronic resonance, such as NQR, NMR or ESR, which is indicative of a particular substance. Signal processing methods involving HTLS, HSVD, MPM, MMPM, FFT, STFT and STMPM are also described.