Hertz is a unit of frequency (of change in state or cycle in a sound wave, alternating current, or other cyclical waveform) of one cycle per second.

AC current in the US has a frequency of 60 Hz. An FM station at 100 on the FM dial has a carrier frequency of 100 million cycles per second, or 100 megahertz.

The unit is named after Heinrich Hertz, German physicist.

The frequency response of the human ear is generally agreed to be from 20 hertz (Hz) to 20,000 hertz. The lowest sounds in music are called bass notes, and sound below 80 -100 Hz is considered deep bass. Hertz is the term for how fast something cycles or vibrates per second. If you had something turning or going back and forth 20 times a second, (or 1,200 times a minute,) that thing would have a frequency of 20 hertz. The higher the frequency (the faster the motion), the higher in pitch the sound will be, and the lower the frequency (The slower the motion), the lower the pitch.

If you have ever had engine noise leaking into your car stereo sound, you will remember that the noise rose and fell in pitch with the engine, letting you “hear” the engine’s speed. In a standard speaker with multiple cones, an electronic device called a crossover splits the music signal and sends the proper frequencies to each cone.

Named after physicist Heinrich Hertz, Hertz is a measurement of how often something happens. Specifically, it's the number of times something happens every second. For example, say you have a piano string tuned to produce the note of A4. When you strike it, it will vibrate 440 times every second. This is a frequency -- literally, how frequent the event of it moving back and forth is -- of 440 Hertz, or 440Hz for short.

LFOs can move back and forth very slowly. If one repeated every two seconds, you could say it has a frequency of 0.5Hz, meaning it manages to make another half of a cycle every second.

The phrases Hertz and frequency only make sense when applied to something that happens again and again. An envelope only plays out once every time a note is pressed, so it doesn't have a frequency and cannot be measured in Hertz. Oscillators continually move back and forth, so they can be measured in Hertz.

The human range of hearing is generally thought to span from about 20Hz to about 20,000Hz. As you may gather from kilograms and kilometres, kilo means a thousand, so we can call 20,000Hz 20 kilohertz, or 20kHz for short. So to put it another way, the human range of hearing is roughly 20Hz to 20kHz.

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