Abstract: For speech signals that represent a wave form and include a sequence of samples, a method is provided for modifying the time scale of the speech signals. The method includes estimating the number of the samples that constitutes a pitch period. The estimate is made by a plurality of pitch estimators that operate in parallel and process peak and/or valley measurements of the wave form. The method also includes combining a first group of samples with a second group of samples to form a combined group. Each group consists of the same number of sequential samples from the sequence of samples. The number of samples in each group is equal to the estimated number of samples that constitutes a pitch period. The second group of samples immediately follows the first group in the sequence of samples. According to another feature of the invention, the method includes determininq whether the time scale of the speech signals is to be compressed or expanded.