The Matlab code presented here is an example of Cross-Synthesis – a technique of impressing the spectral envelope of one sound (modulating signal) on the flattened spectrum of another (carrier signal), consisting of the following steps:
1. Short-Time Fourier Transform (STFT) of both the modulator and carrier signals;
2. Extraction of the spectral envelope of each time-frame of the signals;
3. Division of the spectrum of each carrier frame by its own spectral envelope in order to flattening it;
4. Multiplication of the flattened carrier spectral frame by the envelope of the corresponding modulator frame;
5. Inverse Short-Time Fourier Transform (ISTFT) of the resultant time-localized spectrum.
The code is based on the theory described in:
 J. Smith. Spectral Audio Signal Processing.W3K Publishing, 2011.
 U. Zölzer. DAFX: Digital Audio Effects. Chichester, John Wiley & Sons, 2011.