Imagine an old man with a deep, booming voice. Now imagine a young child with a high, piercing scream. The old man’s voice has a low pitch, and the young child’s voice has a high pitch. To be scientific, the old man’s vocal cords are vibrating at a slower rate than the child’s. If you somehow managed to count how many times the man’s vocal cords vibrated in one second, you would then know the frequency of the pitch his voice is creating. Frequency is the scientific measurement of pitch, and the unit of measurement is called Hertz, or Hz for short.

When people speak, they use many different pitches. You may have noticed that when someone asks a question, their voice goes up at the end of the sentence. In this case, it doesn’t really matter exactly how much it goes up, as long as it noticeably goes up. In music, we have to be more precise. It matters exactly what frequency we start on and exactly how far we go up (or down).

In western music, we somewhat arbitrarily decided that we would use 440Hz as a starting point. Something vibrating 440 times per second will produce a pitch that we have given a name: “A.” Just like someone somewhere had to decide how long an inch was, someone decided that there is a note called “A” and it has a frequency of 440 Hz. I won’t go into the history, but in the west, we have landed on a system called “equal temperament” that describes all the other notes and their exact frequencies.

(There is debate about whether 440Hz is the best choice for “A”, and there is also debate about whether equal temperament is the best tuning system, but that’s not what this book is about.)