Estimation is the task of computing the spectral envelope of a signal. First, the general requirements for this step will be introduced in section 3.1, then the estimation methods LPC, cepstrum, and discrete cepstrum will be described in the following sections 3.2-3.5. These descriptions will proceed from a non-formal introduction (what the algorithm does) to a detailed formal development (how it is done), in some cases followed by a definition of the class of the algorithm in the taxonomy of signal processing systems. For the discrete cepstrum method, an evaluation will be presented in section 3.6.
As the methods for spectral envelope estimation described in this chapter all have their strong and weak points, depending on the signal and the needs of the user, all methods have been implemented in the spectral envelope library, to keep it as flexible as possible.