Linear interpolation is used to provide a much cleaner sound when frequency modulation is used. When FM is used with no interpolation there is some hiss associated with the frequency shift as the closest available sample is used when really it should be somewhere in between. Interpolating between samples provides a smoother mapping from one frequency to the other by providing the necessary in-between samples (oversampling if the hardware rate is higher than the file rate). There is a small time overhead in doing the interpolation so there is an option to turn it off in case there is too much of a performance hit on foreground operation.

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