Method and apparatus for controlling the operation of an emotion synthesizing device, notably of the type where the emotion is conveyed by a sound, having at least one input parameter whose value is used to set a type of emotion to be conveyed, by making at least one parameter a variable parameter over a determined control range, thereby to confer a variability in an amount of the type of emotion to be conveyed. The variable parameter can be made variable according to a variation model over the control range, the model relating a quantity of emotion control variable to the variable parameter, whereby said control variable is used to variably establish a value of said variable parameter. Preferably the variation obeys a linear model, the variable parameter being made to vary linearly with a variation in a quantity of emotion control variable.