System and method for determining a first formant analysis filter and prefiltering a speech signal for improved pitch estimation

摘要

The present invention comprises an improved vocoder system and method for estimating the pitch of a speech signal. The speech signal comprises a stream of digitized speech samples. The speech samples are partitioned into frames. For each frame of the speech signal, an optimal order-two inverse filter is determined. The optimal order-two inverse filter is determined by computing an order-two inverse filter at various locations within the speech frame. For each order-two inverse filter an energy value is calculated which represents the proportion of energy which would remain if the speech signal were filtered with the order-two inverse filter. The order-two inverse filter which minimizes the energy proportion is chosen to be the optimal order-two inverse filter. The optimal order-two inverse filter is then used to filter the samples of the speech frame. An autocorrelation is performed on the filtered signal for a range of tine-delay values. The peaks of the autocorrelation function are analyzed to determine the pitch period.