A method for updating the processing capacity of an encoder or decoder to use a modulated transform having a size greater than a predetermined initial size is provided, particularly, where the encoders or decoders are for storing an initial prototype filter defined by an ordered set of initial size coefficients. A step is provided for constructing a prototype filter of a size greater than the initial size to implement the modulated transform of the greater size by inserting at least one coefficient between two consecutive coefficients of the initial prototype filter.