Adaptive synthesis filter factorisation for postfiltering

An adaptive time-domain postfiltering technique based on the synthesis linear prediction (LP) filter factorisation is proposed. The factorisation is performed using the relation between the LP filter poles and formants. This technique enables more control on the formants and valleys shape. Pole locations representing the main formant and optimum shaping constants for each formant are searched to make narrower main formant bandwidth while maintaining other formant information and more attenuation in valley regions.