1. A computer-implemented method of training a hidden trajectory model, of a speech recognition system, which generates Vocal Tract Resonance (VTR) targets, the method comprising: obtaining initial VTR target parameters using speaker-independent training; storing the initial VTR target parameters as generic VTR target parameters; iteratively updating the generic VTR target parameters, for each of a plurality of speakers in a training set, using speaker-adaptive training to generate updated generic VTR target parameters, wherein iteratively updating the generic VTR target parameters, for each particular speaker of the plurality of speakers in the training set, further comprises iteratively scaling the generic VTR target parameters using a corresponding speaker-dependent scaling factor for the particular speaker to generate the updated generic VTR target parameters; storing the updated generic VTR target parameters on a computer storage medium, for use by a target selector to generate VTR sequences, as the generic VTR target parameters in order to configure the hidden trajectory model to perform speech recognition; and performing speech recognition using the configured hidden trajectory model.