1. A method for storing data indicative of an input analog signal in the form of rectangular coordinates X and Y values in a memory and producing an output signal substantially identical to the input analog signal from the stored data, comprising the steps of: defining an elementary interval (T) on an X-axis of an X-Y coordinate system on which the input analog signal is superimposed and selecting a first series of points separated along the X-axis by interval T, interval (T) providing points which are sufficiently close together to enable them to be connected to form a curve similar to the curve of the input signal; selecting a second series of points which is a subset of the first series by establishing a threshold ratio between a chord separating two non-consecutive points and the sum of chords separating each of the consecutive points within the two non-consecutive points; and selecting an interval between these two non-consecutive points to correspond to the maximum ratio below the threshold, in that the address of the points of each group of three non-consecutive points determined in this way is established as well as the number of elementary intervals (T) between them and their respective amplitudes (a.sub.1, .sub.2 and a.sub.3); storing in a memory, the address and the amplitude, which are the X and Y values, of the isolated points which do not come within a group of three non-consecutive points; and generating, from the data previously stored in memory, an output analog signal corresponding to the input analog signal by establishing between each group of three-non-consecutive points a parabola with respect to an axis of symmetry corresponding to the axis of the elementary intervals from the equation: EQU Y.sub.(T) =AT.sup.2 +BT+C in which: A=(a.sub.1 +a.sub.3 -2a.sub.2)/2T.sup.2 B=(a.sub.3 -a.sub.1)/2T C=a.sub.2.