Experimental results on the audibility of phase distortion produced by minimum-phase 4-kHz 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 diotically (same signal at both ears) on earphones. Group-delay distortion was doubled, progressively, until at least 67% mean correct discrimination was attained. At 4 kHz 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 15 kHz 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.
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