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Experimental results on the audibility of phase distortion produced by minimum-phase 4kHz and 15 kHz anti-alias filters are reported. Numerous impulse response pairs with identical spectral magnitudes but linear-phase and minimum-phase responses were compared by five test subjects who listened dichotically on earphones. Group-delay distortion was doubled, progressively, until at least 67% mean correct discrimination was attained. At 4kHz, the phase distortion introduced by a cascade of two eighth-order Butterworth filter pairs was audible as was that from only a single pair of seventh-order elliptic filters. At 15kHz, the cascade of up to 4 pairs of seventh-order elliptic filters introduced no perceptible effects. Experimental details and several representative filter frequency and transient responses are included.