Finally, both the VIEWENV program and the spectral envelope library and programs have already been applied in a project in the analysis-synthesis team [Hen98]. The topic was analysis and synthesis-by-rule of the singing voice. The spectral envelopes of recordings of a singer were estimated with the spectral envelope library, after which the displaying and measuring capabilities of the VIEWENV program were used to retrieve the formants and their parameters to set up rules describing the dependencies of the formants on pitch. Also, the SDIF file format for spectral envelopes was used for the first time.