What Is a Hertz? Understanding Frequencies Simply

7.83 Hz, 432 Hz, 528 Hz… In the world of frequencies, the hertz is everywhere. But what exactly does it measure? This short guide explains, without jargon, what a frequency is and how to read these numbers.

The hertz, the unit of frequency

A frequency is the number of times something repeats in one second. The hertz (Hz) is its unit: 1 Hz means one repetition per second.

• A resting heart beats about 60 times a minute, roughly 1 Hz.
• The Schumann resonance oscillates 7.83 times per second: 7.83 Hz.
• The A of a tuning fork vibrates 440 times per second: 440 Hz.

The unit is named after the German physicist Heinrich Hertz, who demonstrated the existence of electromagnetic waves at the end of the 19th century.

Multiples of the hertz

• 1 kHz (kilohertz) = 1,000 Hz
• 1 MHz (megahertz) = 1,000,000 Hz (FM radio, around 100 MHz)
• 1 GHz (gigahertz) = 1 billion Hz (Wi-Fi, at 2.4 or 5 GHz)

Frequency and sound

A sound is a vibration of the air. Its frequency determines its pitch: the higher the frequency, the higher the sound.

• The human ear perceives sounds from about 20 Hz to 20,000 Hz. The upper limit decreases with age.
• Below 20 Hz is infrasound: inaudible, like 7.83 Hz.
• Above 20,000 Hz is ultrasound, which dogs and bats, for example, can perceive.

Doubling a frequency raises the sound by one octave: 220 Hz, 440 Hz and 880 Hz are three successive A notes.

Electromagnetic frequency vs sound frequency

Be careful not to confuse two things that share the same unit:

• A sound wave is a vibration of matter (air, water). It needs a speaker to be produced.
• An electromagnetic wave is an oscillation of an electric and magnetic field. It travels even through a vacuum. Light, radio and the Schumann resonance are electromagnetic waves.

The Schumann resonance is therefore electromagnetic: it isn’t a sound. That’s why our generator emits 7.83 Hz through coils, which produce a very low-intensity electromagnetic field, and keeps its jack output for audible frequencies like 432 Hz or 528 Hz.

What is a sine wave?

A sine wave is the simplest and “purest” waveform: a regular, smooth oscillation with no harmonics. It’s what a tuning fork produces. Frequency generators generally use this type of wave because it corresponds to exactly one frequency.

In summary

• The hertz measures the number of repetitions per second.
• The ear hears from 20 to 20,000 Hz; below that is infrasound.
• Sound and electromagnetic waves use the same unit but are different in nature.
• The Schumann resonance is electromagnetic, not sound.

Further reading

• Schumann Resonance: Everything You Need to Know About the 7.83 Hz Frequency
• 432 Hz vs 440 Hz: Where the Debate Comes From and How to Test It
• Frequency Generator: 7 Criteria for Choosing the Right One