Figure 1.

Perception of the sound of running water as natural does not change at varied playback speed. (A) Diagram of the change of a simple sound, when its playback speed is slowed down twofold. Top: frequency–temporal envelope of a sample chirp. Bottom: chirp sound waveform. Left: Original sound. Right: Sound slowed down by a factor of 2. Note that the sound becomes longer and its center frequency is decreased by a factor of 2. (B) Experiment 1. Mean ratings by 30 adult human subjects of the recording of a natural brook, played back at five different speeds (×1/4 slowed down by a factor of 4; ×1/2 slowed down by a factor of 2; Original; ×2 accelerated by a factor of 2; ×4 accelerated by a factor or 4), on the scale from 1 (most unnatural) to 7 (most natural). Error bars = SEM. There was no significant effect of speed on the rating in a one-way ANOVA [F(4, 26) = 1.030, n.s.)], and the pair-wise comparison with Dunnett correction for multiple comparisons did not reveal any significant differences between mean ratings of sounds with varying speed of playback and the original recording.