A method of converting a plurality of input signals on first and second converters, such that the first and second converters are both used when the plurality of signals comprises two signals, characterised in that said method comprises: selecting more than two input signals; determining the type of each selected signal; combining any signals having the same type to form a combined signal; converting one type of signal with the first converter; converting a second type of signal with the second converter wherein the first or second type signals is a combined signal.