AM radio can be sent over larger distances, but the quality of the sound is not as good as a later kind of radio signal processing, called frequency modulation.

VOA: special.2010.12.08

Maybe you can put the frequency of the higher pitches as high so you can detect the sound quicker and That's it exactly.

大概是把频率调到更高的音高后,就能更敏捷地感觉到声音的变化,而那就是原因了

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