Foundations
A shortcut to knowledge
Warning
This page is work in progress - some information might be wrong or incomplete.
What is sound
We need to begin with some foundations, and a good place to start is by clarifying key language concepts before building on them.
- Sound refers to vibrations that travel through air or another medium and can be perceived by the human ear. It belongs to the physical and organic world of pressure waves that reach our hearing.
- Audio on the other hand is the representation of sound in a form that can be recorded, processed, transmitted, or reproduced. When we speak of audio we are usually working with analog or digital signals that allow us to capture and manipulate sound.
In short, sound is the phenomenon itself, and audio is how we store, process, and recreate it.
About sound
Sound is all around us in daily life, from the music we enjoy to the hum of traffic outside the window. At its simplest, sound is a vibration that moves through a medium such as air, water, or even metal. Our ears pick up these vibrations and our brain interprets them as what we recognize as sound. This is why there can be no sound in the vacuum of space: without air or another material to carry vibrations, there is nothing for our ears to hear.
When we look deeper into sound as a wave, we can describe it with several key properties:
Key properties of sound
Frequency
Frequency refers to how many times the wave repeats per second and is measured in hertz. Frequency can also be outside of human hearing scope (20hz - 20khz).
Sound waves with frequencies below the lower limit of human audibility (generally 20 Hz). Humans cannot hear infrasound but may feel it as a vibration if the sound pressure is Earthquakes, the movement of tectonic plates, and potentially wind in large natural formations.
Pitch
Pitch is how our ears perceive frequency, with higher frequencies heard as higher notes and lower frequencies as deeper tones.
Wavelength
Wavelength describes the physical distance between two repeating points in the wave, such as peak to peak. Phase explains the alignment of two or more waves, which determines whether they reinforce each other or cancel out when combined.
Together these concepts give us a framework to understand how sound behaves in both natural hearing and technical audio processing.
Other factors affecting sound
Other factors affecting how sound travels are temperature and humidity. Although their influence is usually small and often ignored in everyday situations, they still play a role in how sound behaves. In precise acoustic measurements or professional audio work, these factors can make a measurable difference and are worth understanding.
Temperature
Temperature affects the speed and clarity of sound as it moves through the air. When the air is warm, molecules vibrate faster and carry sound waves more efficiently, increasing the speed of sound. In contrast, cooler air slows down molecular motion, reducing sound speed and sometimes causing sound to bend or refract, especially over long distances. This is why sound often travels farther and clearer on warm days compared to cold ones.
Humidity
Humidity influences sound by changing the air’s density. Moist air contains more water vapor, which makes it lighter and allows sound waves to move more freely. As humidity increases, sound tends to travel faster and lose less energy along the way. In dry air, the opposite occurs, with sound waves slowing down and becoming slightly weaker over distance.
Human hearing
Hearing Range
The average human ear can detect sounds between 20 and 20,000 hertz. Frequencies below 20Hz are called infrasound and are usually felt more as vibration than heard, while frequencies above 20kHz are called ultrasound and lie beyond human perception.
With age or exposure to loud sounds, the upper limit of hearing tends to decrease, which is why older individuals often struggle to hear very high tones.
Frequency Sensitivity
Human hearing is not equally sensitive across all frequencies. The ear is most responsive to sounds in the range of about 2kHz to 5kHz, where many speech sounds and vocal tones occur. Low frequencies, such as deep bass, must be played at higher volumes to be perceived at the same loudness as mid-range sounds. This variation in sensitivity explains why the same sound can seem louder or softer depending on its pitch.
Sound in context of studio
- Sound proofing, why?, how? types of panels,