Patent ID: 8670981

Claim:
A method of determining line spectral frequency vectors representing filter coefficients for a time-varying filter for encoding speech according to a source-filter model, whereby speech is modeled to comprise a source signal filtered by the time-varying filter, the method comprising: receiving a speech signal comprising successive frames; for each of a plurality of frames of the speech signal, deriving a first line spectral frequency vector for a first portion of the frame, and a second line spectral frequency vector for a second portion of the frame; and calculating a transmit line spectral frequency vector and an interpolation factor based on the first and second line spectral frequency vectors, and on the transmit line spectral frequency vector for a preceding one of the frames, wherein calculating the transmit line spectral frequency vector and the interpolation factor is based on minimizing a difference between the second line spectral frequency vector and the transmit line spectral frequency vector and between the first line spectral frequency vector and an interpolated line spectral frequency vector based on the interpolation factor and the transmit line spectral frequency vector, the minimizing a difference based, at least in part, upon minimizing a residual energy for the frame.