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Sound waves are vibrations that travel through the air or another medium and can be heard when they reach an observer's ear. Essentially, sound is the rapid variations in air pressure caused by these vibrations. When an object vibrates, it creates a mechanical wave in the medium surrounding it—typically air—causing particles to oscillate.

These waves move out from the source of the sound and are characterized by their wavelength, frequency, amplitude, and speed. Wavelength is the distance between repeating units of a wave pattern, while amplitude relates to the force of the vibration and is perceived as the loudness of the sound. Speed is how fast the wave travels through the medium, which in air at room temperature is approximately 343 meters per second. Sound waves exist as both longitudinal waves, where particle displacement is parallel to the direction of wave travel, and, less commonly, as transverse waves, where displacement is perpendicular.

Hertz (Hz) is the unit of measurement for frequency, named after the German physicist Heinrich Hertz. It quantifies the number of times a repetitive event occurs in one second. When it comes to sound waves, frequency specifically refers to how often the particles of a medium vibrate when the sound wave passes through it.

One Hertz equals one cycle per second. Therefore, if a sound wave has a frequency of 440 Hz, it means that the wave cycles 440 times in one second. Frequency is a crucial component in determining the pitch of a sound: generally, the higher the frequency measured in Hertz, the higher the perceived pitch. Conversely, a lower frequency sound wave will result in a lower pitch.

When discussing the perceptual properties of sound, we're mainly referring to characteristics that are perceived by our ears and interpreted by our brain. Pitch is one of these key characteristics and can be thought of as how 'high' or 'low' a sound is.

To understand this, imagine a piano keyboard. When a key on the left side (the lower end) is pressed, it results in a low-pitched sound. A key on the right side (the higher end) produces a high-pitched sound. However, the pitch we perceive is not just a simple reflection of frequency; it is also influenced by the individual's auditory perception, which can be affected by factors such as age or potential hearing loss.

It's crucial to distinguish between the objective and subjective properties of sound. Objective properties, such as frequency, can be precisely measured and described without bias. They are concrete and not influenced by individual perceptions.

On the other hand, subjective properties are exactly that—subject to interpretation. Pitch is a subjective aspect of sound since it's determined by how an individual's brain interprets the frequency of sound waves. Two people might perceive the pitch of a sound differently due to variations in their hearing ability. Additionally, subjective experiences of sound can include qualities like timbre, which describes the unique sound signature of an instrument or voice, influencing how 'colorful' or 'rich' a sound appears.