Frequency is the number of waves per unit of time, and in sound is heard as pitch

As is true for all waves, there are four main characteristics of a sound wave: frequency, wavelength, period, and amplitude. Frequency is the number of waves per unit of time, and in sound is heard as pitch. High-frequency (≥15.000Hz) sounds are higher-pitched (short wavelength) than low-frequency (long wavelengths; ≤100Hz) sounds. Frequency is measured in cycles per second, and for sound, the most commonly used unit is hertz (Hz), or cycles per second. Most humans can perceive sounds with frequencies between 30 and 20,000 Hz. Dogs detect up to about 40,000 Hz; cats, 60,000 Hz; bats, 100,000 Hz; and dolphins 150,000 Hz, and the American shad (Alosa sapidissima) fish can hear 180,000 Hz. Those frequencies above the human range are called ultrasound.

Pitch can only be determined only in sounds that have a frequency that is clear and stable enough to distinguish from noise. Sound with a distinct frequency can be produced by many different instruments and devices, such as vibrating string or air column. Frequency is dependent on wavelength and the speed of sound, and it can be calculated with the following equation: f=v/λ.

Key Points

• Pitch is the measure of how “high” or “low” something sounds.

• Frequency is the number of waves per unit of time, and in sound is heard as pitch.

• Frequency is dependent on wavelength and the speed of sound, and it can be calculated with the following equation: f=v/λ

Key Terms

Pitch: Perception of frequency

Frequency: The quotient of the number of times (n) a periodic phenomenon occurs over a unit of time (t): f = n / t.

Hertz: In the International System of Units, the derived unit of frequency; one (period or cycle of any periodic event) per second. Symbol: Hz