The present code is a Matlab function that provides envelope extraction of the amplitude spectrum of a given signal via shape-preserving piecewise cubic interpolation of the spectral peaks and moving average filtration of the result. The function is similar to (but not the same as) the Matlab function “envelope”.
An example is given in order to clarify the usage of the function. For convenience, the input and output arguments are given in the beginning of the function.
The code is based on the theory described in:
 D. Schwarz, X. Rodet. Spectral Envelope Estimation and Representation for Sound Analysis-Synthesis. Proceedings of the ICMC 1999, pp. 351-354.