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  • General

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  • 音频频率和音响

    A marching band in uniform parades down a street, playing various musical instruments.

    A marching band passes you as it parades down the street. You heard it coming from several blocks away. Now that the different instruments have finally reached you, their distinctive sounds can be heard. The tiny piccolos trill their bird-like high notes, and the big tubas rumble out their booming bass notes. Clearly, some sounds are higher or lower than others.
    ::游行乐队在街上游行时经过你。你听到它从几条街外传来。现在不同的乐器终于到达你面前,它们的独特声音可以被听到。小比科洛斯的象鸟般的高音响,大喇叭响起他们的低音音响。显然,有些声音比其他声音高或低。

    High or Low
    ::高或低

    How high or low a sound seems to a listener is its pitch . Pitch, in turn, depends on the frequency of . is the number of waves that pass a fixed point in a given amount of time. High-pitched sounds, like the sounds of the piccolo in the Figure , have high-frequency waves. Low-pitched sounds, like the sounds of the tuba Figure , have low-frequency waves. 
    ::听者看声音看似高低的音量是它的投影。 投影取决于. 的频率。 投影取决于在一定时间内通过固定点的波的频率。 高音量,如图中的piccolo声音,有高频波。 低音量的声音,如波形图的声音,有低频波。

    Comparison of a piccolo and a tuba illustrating high and low pitch sounds.

    Can You Hear It?
    ::你能听到吗?

    The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound . Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 hertz are called . Ultrasound is too high-pitched for humans to hear.
    ::声音波的频率以赫兹(Hz)测量,或以一秒内通过固定点的波数测量。通常,人类可以听到声音,频率在20赫兹至20,000赫兹之间。频率低于20赫兹的声音被称为次声。次声太低,人类听不见。频率超过20,000赫兹的声音被称为超声波,人类听不见超声波太高。

    Some other animals can hear sounds in the ultrasound range. For example, dogs can hear sounds with frequencies as high as 50,000 Hz. You may have seen special whistles that dogs—but not people—can hear. The whistles produce sounds with frequencies too high for the human ear to detect. Other animals can hear even higher-frequency sounds. Bats, like the one pictured in the Figure , can hear sounds with frequencies higher than 100,000 Hz!
    ::其它动物可以在超声波范围内听到声音。 例如,狗可以听到频率高达5万赫兹的声音。 您可能已经看到过狗(而不是人)能够听到的特别哨声。 哨声产生的频率太高,人类耳朵无法探测到。 其他动物甚至可以听到高频的声音。 蝙蝠,如图中的蝙蝠,可以听到频率超过10万赫兹的声音!

    A bat in flight, illustrating its ability to use ultrasound for navigation.

    Q: Bats use ultrasound to navigate in the dark. Can you explain how?
    ::问题:蝙蝠用超声波在黑暗中导航。你能解释一下吗?

    A: Bats send out ultrasound waves, which reflect back from objects ahead of them. They sense the reflected sound waves and use the information to detect objects they can’t see in the dark. This is how they avoid flying into walls and trees and also how they find flying insects to eat.
    ::A:蝙蝠发出超声波,它们从前面的物体反射回来。 它们感知反射声波,并利用信息探测在黑暗中看不到的物体。 这就是它们如何避免飞向墙壁和树木,以及如何发现飞虫吃东西。

    Use the Violin simulation below to play different musical notes and observe the graph of Frequency vs Amplitude produced by the violin strings vibrating at different tensions:  
    ::使用下面的Violin模拟来播放不同的乐笔, 并观察小提琴弦在不同紧张状态下振动产生的频率与振幅图:

    Further Reading
    ::继续阅读

    Summary
    ::摘要

    • How high or low a sound seems to a listener is its pitch. Pitch, in turn, depends on the frequency of sound waves.
      ::听者看声音有多高或低是其投影。 投影取决于声波的频率。
    • High-frequency sound waves produce high-pitched sounds, and low-frequency sound waves produce low-pitched sounds.
      ::高频声波产生高音量声音,低频声波产生低音量声音。
    • Infrasound has wave frequencies too low for humans to hear. Ultrasound has wave frequencies too high for humans to hear.
      ::次声波频率太低,人类听不到。超声波频率太高,人类听不到。

    Review
    ::回顾

    1. What is the pitch of sound?
      ::声音是什么声音?
    2. How is the pitch of sound related to the frequency of sound waves?
      ::声波的频率与声波的频率如何相关?
    3. Define infrasound and ultrasound.
      ::定义次声波和超声波。