Patent ID: 8891708

Claim:
A method for filtering an input signal representing audio or video information to generate an output signal representing the audio or video information with a specified phase shift that is a non-zero function of frequency, wherein the method comprises: receiving the input signal in a forward direction at an input terminal; applying a forward filter and a backward filter coupled in cascade with one another to the input signal, wherein the forward filter applies its filtering operation to its input in the forward direction and the backward filter applies its filtering operation to its input in a backward direction that is opposite the forward direction; and generating an output signal at an output terminal in response to filtered signals received from the cascade of forward and backward filters, wherein the output signal has the specified phase shift that is a non-zero function of frequency; wherein the filtering operation of the backward filter has a phase shift that is a function of frequency and the filtering operation of the forward filter has the specified phase shift that is a non-zero function of frequency defined relative to the phase shift of the filtering operation of the backward filter, and the backward filter is applied to a series of input segments of its input signal to generate its output signal in a series of output segments, wherein: a respective segment of input comprises a look-ahead-interval signal and a processing-interval signal following the look-ahead-interval signal in the direction the backward filter is applied, the look-ahead-interval signal also being present in one or more other input segments, and a respective output segment comprises a filtered look-ahead-interval signal followed by a phase-shifted-signal in the direction the backward filter generated the output segment, each phase-shifted-signal generated by the backward filter being applied to the processing-interval signal of a respective input segment; deriving an amplitude adjustment from amplitudes of: an end of the filtered look-ahead-interval signal that is adjacent to the phase-shifted signal in a specified output segment, and an end of the phase-shifted signal in a subsequent output segment that is opposite an end of the phase-shifted signal in the subsequent output segment that is adjacent to the filtered look-ahead-interval signal in the subsequent output segment; and applying the amplitude adjustment to the phase-shifted signal in the subsequent output segment to reduce a difference in amplitude with an end of the phase-shifted signal that is adjacent the look-ahead-interval signal in the specified output segment, wherein the amplitude adjustment is modified so that it converges to zero as it is applied to the phase-shifted signal in the forward direction.