Chapter 1 – Audio Fundamentals (I): How Sound Is Produced

1. What Is Sound?

Sound is a mechanical wave that propagates through a medium such as air, water, or solid materials.

In daily life, we usually hear sound through air, which is also the most common medium for audio products.

Sound is generated by a vibrating object, causing the air molecules around it to compress and rarefy alternately, forming a wave that travels outward.

When the wave reaches our eardrum, it vibrates and is recognized by the brain as sound.

2. Basic Parameters of Sound

Frequency (Hz)

Frequency refers to the number of vibrations per second.

Unit: Hertz (Hz)

Humans can generally hear the range from 20 Hz to 20 kHz.

• Low frequency = bass
• High frequency = treble

Amplitude

Amplitude refers to the intensity or strength of the sound wave.

It determines how loud or soft the sound is.

The larger the amplitude, the louder the sound.

Sound Pressure Level (SPL)

SPL is used to express the loudness of sound.

Unit: decibel (dB)

A typical conversation is about 60 dB, while a rock concert can reach 110 dB or higher.

Waveform

Waveform refers to the shape of the sound wave.

Different waveforms produce different timbres.

For example, a sine wave sounds pure, while a complex waveform sounds richer.

Harmonic and Distortion

A pure tone contains only the fundamental frequency.

Real sound contains multiple harmonics.

When unwanted harmonics appear, it becomes distortion, which affects sound quality.

3. How the Human Ear Works

The human ear consists of three parts:

• Outer ear
• Middle ear
• Inner ear

Sound waves enter the ear canal and vibrate the eardrum.

These vibrations are transmitted to the cochlea, which converts them into electrical signals.

Finally, the brain analyzes these signals and recognizes them as different sounds.

The human ear is most sensitive in the frequency range of 2 kHz to 5 kHz, which is also the key range for human voice clarity.

4. Summary

Sound is produced by vibration, transmitted through a medium, and perceived by the ear.

Understanding the basic parameters and how the ear works is the foundation for learning audio technology.

Whether you are developing speakers, amplifiers, or tuning audio systems, it all starts with a deep understanding of sound itself.