The effect of frequency bandwidth on perceptual time-axis resolution of a digital audio signal was studied experimentally. Four kinds of pulse train having constant intervals were used for the test signal. To make the test signal, the upper frequencies were limited using an FIR low-pass filter. Cutoff frequencies of the FIR low-pass filter were 40 kHz and 20 kHz. The experiment was performed in a room with a volume of 54.7 m3, reverberation time of 0.36 s (at 1 kHz), and noise level of NC-25. As the reference signals, pulse trains having designated intervals 1, 0.5, 0.25, and 0.125 s were used. On the other hand, pulse train having slightly different intervals from the reference signals (maximum+20% to -20% were used as the test signals. Reference signals and test signals were presented alternately to the subjects. The subjects were asked whether the test signal is equal to the reference signal or not by hearing. The subjects were 11 males, age 22 to 24, having normal hearing. Purpose of this experiment is to confirm the following hypothesis. Since the waveform of a pulse signal reproduced by the 40-kHz bandwidth system is more similar to the original signal than by the 20-kHz bandwidth system. We can assume that the subjects would be able to identify the interval of the test signal more easily and more correctly using the 40-kHz system thab using the 20-kHz system. When the interval of the test signal is short, identification becomes easier, but when it becomes long, identification becomes rather difficult. As a result of the experiment, we found that widening the frequency band improves perceptual time-axis resolution of a digital audio signal. Adoption of higher sampling frequency will be helpful from the viewpoint of improving the time-axis resolution.
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