The invention provides a method of producing a mass spectrum, comprising: obtaining a transient from the oscillation of ions in a mass analyser; Fourier transforming the transient to obtain a complex spectrum having a real component and an imaginary component; and calculating an enhanced spectrum which comprises a combination of (i) and (ii) wherein (i) comprises a Positive spectrum; and (ii) comprises an Absorption spectrum. Also provided are an apparatus for producing a mass spectrum suitable for carrying out the method as well as a method of determining a phase correction for a complex spectrum obtained by Fourier transformation from a detected transient obtained from a mass analyser.