Complex sounds

Another difference you may have noticed between sounds is that some sounds are pleasant while others are unpleasant. A beginning violin player sounds very different than a violin player in a symphony, even if they are playing the same note. A violin also sounds different than a flute playing the same pitch. This is because they have a different tone, or sound quality. When a source vibrates, it actually vibrates with many frequencies at the same time. Each of those frequencies produces a wave. Sound quality depends on the combination of different frequencies of sound waves.


Imagine a guitar string tightly stretched. If we strum it, the energy from our finger is transferred to the string, causing it to vibrate. When the whole string vibrates, we hear the lowest pitch. This pitch is called the fundamental. Remember, the fundamental is really only one of many pitches that the string is producing. Parts of the string vibrating at frequencies higher than the fundamental are called overtones, while those vibrating in whole number multiples of the fundamental are called harmonics. A frequency of two times the fundamental will sound one octave higher and is called the second harmonic. A frequency four times the fundamental will sound two octaves higher and is called the fourth harmonic. Because the fundamental is one times itself, it is also called the first harmonic.

How is knowledge useful in everyday life?

The more harmonics a sound has, the fuller the quality the sound is. All the different overtones of a sound help give it a unique pattern. This is especially true for a person’s voice. Everybody in the world has a different voice print, or pattern of overtones. Detectives can track a criminal if they know his voice print just as they would use his fingerprints. Voice identification equipment is used in advanced security systems to recognize and let in only one authorized person. Voice prints are also used in modern technology, for example, voice activated telephones. In the future, if you want the lights on, it may be more common to say, “Turn on lights,” than to flip a light switch.


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