Sound is energy that travels through a medium, such as air or water, in waves. These waves possess distinct characteristics that influence how they are experienced. Frequency is a fundamental aspect of sound, providing insight into the nature of various sounds. This article explores what frequency measures in sound and its impact on auditory perception.
Defining Sound Frequency
Frequency in sound refers to the number of vibrations or cycles that occur in a sound wave per second. It quantifies how often a sound wave repeats itself as it propagates through a medium. This property measures the rate at which pressure variations occur, indicating how rapidly medium particles oscillate.
The standard unit of measurement for frequency is the Hertz (Hz). One Hertz is equivalent to one cycle per second. Higher Hertz values indicate more rapid vibrations and more cycles occurring within the same timeframe.
To visualize frequency, consider ripples from a stone dropped into a pond. Quick, close ripples represent high frequency. Slow, spread-out ripples illustrate low frequency. This reflects the speed of wave repetitions, similar to how a rapidly vibrating guitar string produces more cycles per second than a slowly vibrating one.
How Frequency Shapes Pitch
The frequency of a sound wave influences our perception of its pitch. Pitch refers to how high or low a sound seems to a listener. A higher frequency sound wave is perceived as a higher-pitched sound, such as a whistle. Conversely, a lower frequency sound wave results in a lower-pitched sound, like a bass drum.
Humans typically hear sounds within a frequency range from approximately 20 Hz to 20,000 Hz (or 20 kHz). Individual hearing can vary, and sensitivity to higher frequencies often decreases with age. The human auditory system is most sensitive to frequencies between 2,000 and 5,000 Hz.
Sounds outside this audible range are not perceived as pitch by humans. Frequencies below 20 Hz are termed infrasound; they may be felt as vibrations but do not register as distinct tones. Frequencies above 20,000 Hz are known as ultrasound and are inaudible to the human ear. The correlation between frequency and pitch is fundamental to our auditory experience.
Frequency Versus Loudness
Frequency is often confused with loudness, but they are distinct properties of a sound wave. Frequency measures the rate of vibration, determining a sound’s pitch. Loudness measures a sound’s intensity or volume, relating to the amplitude of the sound wave.
Amplitude refers to the maximum displacement of particles in the medium from their resting position as the sound wave passes. A larger amplitude signifies a more energetic wave, which our ears perceive as a louder sound. These two characteristics, frequency and amplitude, are independent of each other.
Consider a guitar string. Pressing different frets changes the string’s length, altering its vibration rate and frequency, resulting in a higher or lower pitch. Plucking the string with more force increases its amplitude, making the sound louder without changing its fundamental pitch. This demonstrates that a sound can be high-pitched and quiet, or low-pitched and loud, as frequency and loudness are separate attributes.