1. A method for updating a processing capacity of an encoder or decoder in order to use a modulated transform having a size greater than a predetermined size, said encoder or decoder being adapted to store an initial prototype filter defined by an ordered set of coefficients of an initial size, said method comprising: constructing, using a computer processor, a prototype filter of a size greater than said initial size to implement the transform of a size greater than the predetermined size by inserting at least one coefficient between two consecutive coefficients of the initial prototype filter.