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Abstract

An audio special-effect is created by a slow phase shift. A series of all-pass digital filters are used to shift the phase of an input stream of digital-audio samples. The amount of phase shift is determined by filter coefficients. The filter coefficients are increased and decreased to sweep the phase shift up and down over a relatively long period of time such as one second per sweep. The filter coefficients must be continuously re-generated by a processor as each sweep occurs. Coefficient generation loads the processor, reducing performance of other programs and user applications. An exact prior-art method requires a division operation for each coefficient generated. Since division operations are slow, the processor is especially burdened by coefficient generation. An approximate method for coefficient generation eliminates the division operation and instead uses a multiply or a simpler shift operation. The newly-generated filter coefficients are sent from the processor to the all-pass digital filters in a digital-signal processor (DSP) to update the filter coefficients, generating the phase shift special effect.

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First Claim