1. A method for providing spectral speech descriptions to be used for synthesis of a speech utterance comprising the steps of receiving at least one spectral envelope input representation corresponding to the speech utterance, where the at least one spectral envelope input representation includes at least one of at least one formant and at least one spectral trough in the form of at least one of a local peak and a local valley in the spectral envelope input representation, extracting from the at least one spectral envelope input representation a rapidly varying input component, where the rapidly varying input component is generated, at least in part, by removing from the at least one spectral envelope input representation a slowly varying input component in the form of a non-constant coarse shape of the at least one spectral envelope input representation and by keeping the fine details of the at least one spectral envelope input representation, where the details contain at least one of a peak or a valley, creating a rapidly varying final component, where the rapidly varying final component is derived from the rapidly varying input component by manipulating at least one of at least one peak and at least one valley, combining the rapidly varying final component with one of the slowly varying final component and the spectral envelope input representation to form a spectral envelope final representation, and providing a spectral speech description output vector to be used for synthesis of a speech utterance, where at least a part of the spectral speech description output vector is derived from the spectral envelope final representation.