When studying the acoustic signals of animals, it is often necessary to obtain the precise time structure of the frequency. It is also useful to extract the envelope of a signal or to modify a signal to obtain its frequency modulated part. This can be achieved digitally using the analytic signal concept. We deal here with the method. Definition and computation are described, its application is discussed and the performance: are compared to those of sonograph and zero-crossing methods. This paper presents a method enabling precise AM and FM analysis of different animal vocalisations. The method has also been used for the purpose of synthesis by extracting the frequency modulated part of a signal. It is found to be a powerful means of modifying some parameters of a natural signal without altering other features.