What is Sound?
Sound is air pressure waves. When a speaker vibrates, it pushes air forward and pulls it back behind. These pressure differences reach our ear and we hear sound.
Imagine a water surface. When you throw a stone in, circles spread out. Sound works similarly, just in 3D and through air.
Tone, Sound, Noise and Bang
Not all sounds are equal. In acoustics, we distinguish four fundamental types of sound events each with its own characteristics and applications.
Tone
Pure, sinusoidal sound
- Single frequency only
- No overtones
- Sounds "flutey", empty
- Example: Tuning fork, pure sine
Sound
Fundamental + overtones
- Fundamental frequency + multiples
- Overtones provide color
- Sounds "full", natural
- Example: Piano, voice, guitar
Noise
Irregular vibrations
- Many frequencies simultaneously
- No clear pitch
- Random pattern
- Example: Rain, traffic, hiss
Bang
Short, impulsive sound
- Very short duration
- Broad frequency spectrum
- Immediate decay
- Example: Clap, whip, explosion
Visualization: Tone vs. Sound
This graphic shows the crucial difference: A pure tone has only one frequency (top), while a sound consists of fundamental and overtones (bottom). Amplitude determines volume, frequency determines pitch.
Frequency: Pitch
Frequency tells us how fast something vibrates. Measured in Hertz (Hz) vibrations per second.
- 20 Hz Lowest bass, barely audible
- 440 Hz Concert A, the reference frequency
- 1000 Hz Typical speech frequency
- 10,000 Hz High sibilance sounds
- 20,000 Hz Upper limit of human hearing (in young people)
Caution: Start quietly!
Exercise: Hearing Frequencies
- Put on headphones (not too loud!)
- Start the tone at 440 Hz
- Move the slider slowly to the left (lower)
- Notice: Lower frequencies sound "darker", "fuller"
- Move the slider to the right (higher)
- Notice: Higher frequencies sound "brighter", "sharper"
- Where can't you hear the tone anymore? (Age dependent!)
Amplitude: Volume
While frequency determines pitch, amplitude controls volume. Higher amplitude = more pressure = louder.
In the digital world, we measure volume in Decibels (dB). Important: This is a logarithmic scale!
| dB | Volume | Comparison |
|---|---|---|
| 0 dB | Silence | Absolute silence (theoretical) |
| 30 dB | Quiet | Whisper, quiet room |
| 60 dB | Medium | Normal conversation |
| 85 dB | Loud | City traffic (damage threshold over time) |
| 120 dB | Pain | Airplane, rock concert (immediate damage) |
Waveforms: Timbre
Same frequency, different sound? That's due to waveform. A sine is pure, a sawtooth is sharp, a square wave sounds hollow.
The Three Basic Waves:
Sine: The purest form. No overtones, just the fundamental frequency. Sounds soft, "flutey". Kick drums and sub-basses often use sine waves.
Square: Switches abruptly between two states. Contains only odd overtones. Sounds hollow, "8-bit", typical for retro video games.
Sawtooth: Linear rise, abrupt fall. Contains all overtones. Sounds bright, cutting, typical for synth leads.
Experiment in the Audio Lab
On the homepage, find the Audio Lab (bottom left). There you can:
- Select different waveforms (Sine, Square, Saw)
- Test frequencies from 20-2000 Hz
- See the visual waveform
- Compare: How does 440 Hz sound as Sine vs. Saw?
Human Hearing
Our hearing isn't linear. We hear mid frequencies (1-5 kHz) louder than very low or very high at the same physical volume.
That's why mastering uses Loudness Meters (LUFS) that compensate for this effect. A bass needs to be physically louder to sound as loud as a mid tone.
Summary
- Sound = Air pressure waves, caused by vibrations
- Frequency (Hz) = Pitch, how fast something vibrates
- Amplitude (dB) = Volume, how strong the vibration is
- Waveform = Timbre, determined by overtones
- Human hearing range: approximately 20 Hz 20,000 Hz
That's it. No complex math needed just understanding that sound consists of waves we can manipulate.