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A brief review is included of previous work aimed at quantifying the knock intensity from cylinder pressure measurements. This is used to identify some of the methods used in the current study. Digital signal processing techniques are also discussed, since their application to non-repetitive truncated signals can lead to results that are dependent on the techniques used. These problems are illustrated with some examples of windowing, and non-linear phase shift filters. A good correlation is demonstrated between knock severity indices calculated with energy methods in the time domain and the frequency domain. It is argued that it is easier to implement such knock indices in the lime domain. Use has also been made of mass fraction burn calculations in conjunction with data for the onset of knock, for data recorded simultaneously by two different pressure transducers.