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捂上耳朵!解释噪音之谜

2011-11-05  lindan9997
Some sounds are excruciating. Take fingernails squeaking on a chalkboard. The noise makes many people shudder, but researchers never knew exactly why. A new study finds that there are two factors at work: the knowledge of where the sound is coming from and the unfortunate design of our ear canals. 

有一些声音极其刺耳。指甲划过黑板的声音,会令很多人浑身发颤。但是研究人员却找不出确切的原因。一项新的研究发现,有两个因素在发挥作用:一个是听众对于声音来源的认识,另一个是我们耳道那种令人遗憾的形状。

Previous research found that the painful parts of unpleasant sounds appear to be in the middle range of audible frequencies. But scientists didn’t nail down exactly which frequencies or explain why the sounds were painful. So musicologists Michael Oehler of the Macromedia University for Media and Communication in Cologne, Germany, and Christoph Reuter of the University of Vienna asked listeners to rank sounds in a listening test. Fingernails raking against a chalkboard and chalk squeaking against slate were the most unpleasant sounds from a family of recordings, which also included sounds such as Styrofoam squeaks and scraping a plate with a fork. 

先前的研究发现,能够引起不快的声音中那些令人痛苦的部分处在可听频率范围的中间。但是科学家们没有敲定具体频率是多少,也没能解释为什么这些声音令人痛苦。德国科隆的麦克罗米迪亚传媒大学的音乐学家Michael Oehler,以及维也纳大学的Christoph Reuter进行了一场声音测试,让听众为声音分成等级。在一系列录音中,指甲划过黑板的声音、粉笔在石板上的吱吱声高居令人最难受的声音之榜首,其他声音如塑料泡沫摩擦声和叉子刮盘子的声音也在其中。

The researchers then modified the recordings of fingernails and chalk, removing or attenuating various frequency ranges. They also modified the sounds by selectively extracting either the tonal, musical-pitch parts or the scraping, growling, noiselike parts of the sound. Some listeners were told the true source of the sounds, whereas others were told that the sounds were part of contemporary musical compositions. The same listeners then rated the pleasantness or unpleasantness of the sounds while the researchers measured physical indicators of distress: the listeners’ heart rate, blood pressure, and the electrical conductivity of their skin. 

研究者接着把指甲和粉笔的录音进行了修饰,消除或是减小各种各样的频率范围。他们也选择性地去除声调、高音乐音或是摩擦声、隆隆声等像噪音的部分。一部分听众被告知了声音的真实来源,而另一些听众则被告知这些声音是当代乐曲中的一部分。接着,这些听众们就给声音的愉悦程度划等级,研究者则测量那些能够反映痛苦的他们生理上的变化:心率,血压,以及皮肤的导电性。

As they will report next week at the Acoustical Society of America conference in San Diego, California, Oehler and Reuter found that a listener’s skin conductivity changed significantly when the person heard a sound he or she later reported as unpleasant, showing that disturbing sounds do cause a measurable physical reaction. More surprisingly, they found that the frequencies responsible for making a sound unpleasant were commonly found in human speech, which ranges from 150 to 7000 hertz (Hz). The offending frequencies were in the range of 2000 to 4000 Hz. Removing those made the sounds much easier to listen to. Deleting the tonal parts of the sound entirely also made listeners perceive the sound as more pleasant, whereas removing other frequencies or the noisy, scraping parts of the sound made little difference. 

他们的研究成果将会在下周在加利福尼亚州圣地亚哥举办的美国声学协会会议上汇报。Oehler and Reuter发现,当人们听到一个令他们不舒服的声音时,皮肤的导电性会发生显著的变化,这表明,引起恐慌的声音确实能够产生一种可测量的生理反应。更令人惊奇的是,使一种声音听起来不愉快的频率在人们的日常说话中很常见,从150到7000赫兹。最令人不快的频率是在2000到4000赫兹之间。把这些部分去除了之后,声音就会显得不那么令人难受。把声调部分完全去除,也会使听众觉得这个声音听起来好多了。而去掉其他频率或者摩擦声等噪音部分,则没有发生什么变化。

The ratings also changed depending on what the listeners thought the sounds were. If they thought a sound came from a musical composition, they rated it as less unpleasant than if they knew it actually was fingernails on a chalkboard. But their skin conductivity changed consistently even when they thought the chalkboard sound was from music and rated it as less unpleasant. 

听众们所认为的声音的来源也会影响他们划分等级。认为声音是来自于乐曲的人会比知道声音是指甲划过黑板的人觉得这个声音没有那么令人不愉快。但是皮肤的导电性的变化是一致的,即使当他们以为黑板的声音是来自于乐曲,而且觉得它们也没有那么不悦耳。

The researchers suspect that the shape of the human ear canal may be to blame for the pain. Previous studies have shown that the ear canal amplifies certain frequencies, including those in the range of 2000 to 4000 Hz. A loud screech on a chalkboard could be amplified within our ears to painful effect, the researchers propose. 

研究者猜测,人们之所以觉得痛苦,是由于人类耳道的形状造成的。先前的研究表明,耳道会使某些频率增强,包括在2000到4000赫兹之间的频率。研究者解释,在我们的耳朵里,黑板上的吱吱声被扩大了,因此产生了痛苦的感觉。

Combining physiological measurements of pain such as skin conductance with psychological ratings of uncomfortable sounds is new and makes an important point about perception, says Reinhard Kopiez, a musicologist at the Hanover University of Music, Drama and Media in Germany, who was not involved in the study. Kopiez says the research shows just how important context is in the enjoyment of music. “The audience enjoys the performance because of the knowledge about the [artistic] origins of a sound, although the physiological response remains the same as for uncomfortable sounds,” Kopiez says. 

德国汉诺威音乐、戏剧和媒体大学音乐学家Reinhard Kopiez并没有参与这项研究。他评价说,研究中将测量痛苦的生理参数例如皮肤导电性和对声音的心理评分相结合的方法很新颖,对研究知觉也很重要。他说,这项研究表明了在欣赏音乐的过程中,背景有多重要。Kopiez说:“听众们享受表演,是因为他们知道这声音的来源是艺术的,尽管生理上的反应和不愉快的声音是一致的。”

Oehler and Reuter intend to explore the parameters of unpleasant noises further in the future. Knowing what makes certain sounds painful, they say, could help engineers know which frequencies to modify or mask in order to make annoying sounds, such as whining vacuum cleaners, screeching factory machinery, or grating construction equipment, more pleasing to the ears.

今后,Oehler 和 Reuter 还户进一步探究令人不快的噪音的因素。他们说,知道具体是什么使声音显得令人痛苦,可以使设计师们来修饰噪音,诸如吸尘器的呜呜声、工厂机器的刺耳声以及工地上放置设备的声音,显得好听一点。

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