A method of producing mass spectrum data using a mass spectrometer having an ion source and an ion detector, wherein the method includes: acquiring signal mass spectrum data representative of the mass/charge ratio of ions of sample material based on the output of the ion detector during at least one signal acquisition cycle in which ions of sample material generated by the ion source are detected by the ion detector; and acquiring noise mass spectrum data representative of noise in the mass spectrometer based on the output of the ion detector during at least one noise acquisition cycle in which the ion detector does not detect any ions from the ion source; characterised in that the method further includes: subtracting the noise mass spectrum data representative of noise in the mass spectrometer from the signal mass spectrum data to produce modified signal mass spectrum data representative of the mass/charge ratio of ions of the sample material; wherein the or each noise acquisition cycle and the or each signal acquisition cycle respectively includes: producing one or more high voltage pulses having a magnitude of 500V or greater and supplying the one or more high voltage pulses to one or more components of the mass spectrometer so that the noise mass spectrum data subtracted from the signal mass spectrum data includes analogue electronic noise caused by the production of the one or more high voltage pulses and the supply of said pulses to the one or more components; wherein subtracting the noise mass spectrum data from the signal mass spectrum data includes subtracting an amplitude of each mass/charge ratio bin of the noise mass spectrum data from a corresponding/mass/charge ratio bin of the signal mass spectrum data. acquiring signal mass spectrum data representative of the mass/charge ratio of ions of sample material based on the output of the ion detector during at least one signal acquisition cycle in which ions of sample material generated by the ion source are detected by the ion detector; and acquiring noise mass spectrum data representative of noise in the mass spectrometer based on the output of the ion detector during at least one noise acquisition cycle in which the ion detector does not detect any ions from the ion source; characterised in that the method further includes: subtracting the noise mass spectrum data representative of noise in the mass spectrometer from the signal mass spectrum data to produce modified signal mass spectrum data representative of the mass/charge ratio of ions of the sample material; wherein the or each noise acquisition cycle and the or each signal acquisition cycle respectively includes: producing one or more high voltage pulses having a magnitude of 500V or greater and supplying the one or more high voltage pulses to one or more components of the mass spectrometer so that the noise mass spectrum data subtracted from the signal mass spectrum data includes analogue electronic noise caused by the production of the one or more high voltage pulses and the supply of said pulses to the one or more components; wherein subtracting the noise mass spectrum data from the signal mass spectrum data includes subtracting an amplitude of each mass/charge ratio bin of the noise mass spectrum data from a corresponding/mass/charge ratio bin of the signal mass spectrum data. subtracting the noise mass spectrum data representative of noise in the mass spectrometer from the signal mass spectrum data to produce modified signal mass spectrum data representative of the mass/charge ratio of ions of the sample material; wherein the or each noise acquisition cycle and the or each signal acquisition cycle respectively includes: producing one or more high voltage pulses having a magnitude of 500V or greater and supplying the one or more high voltage pulses to one or more components of the mass spectrometer so that the noise mass spectrum data subtracted from the signal mass spectrum data includes analogue electronic noise caused by the production of the one or more high voltage pulses and the supply of said pulses to the one or more components; wherein subtracting the noise mass spectrum data from the signal mass spectrum data includes subtracting an amplitude of each mass/charge ratio bin of the noise mass spectrum data from a corresponding/mass/charge ratio bin of the signal mass spectrum data.