What is Sound?
Every tool you will ever use as a producer, from EQ and compressors to synths and reverb, changes one of a few basic properties of sound. Learn these properties and every later lesson gets easier.
Sound is Vibration
Sound is air pressure moving back and forth. A speaker cone pushes forward and squeezes the air, then pulls back and stretches it. Those pressure waves travel to your ear, and your brain hears them as sound.
Every sound has three basic properties:
- Frequency: how fast it vibrates. You hear this as pitch (low or high).
- Amplitude: how big the vibration is. You hear this as loudness.
- Timbre (say "TAM-ber"): the tone color. It's why a piano and a guitar playing the same note sound different.
Frequency (Pitch)
Frequency is measured in Hertz (Hz), which means vibrations per second. 1,000 Hz is written as 1 kHz.
Humans hear from about 20 Hz (a deep rumble) to 20,000 Hz (a faint, high hiss). The top of that range drops as we get older.
Doubling a frequency raises the pitch by one octave. 110 Hz, 220 Hz and 440 Hz all sound like the note A, each one higher than the last. That's why music software spaces frequencies on a logarithmic scale.
The frequency spectrum
Producers split the range of human hearing into named regions. You'll use these names in every mixing lesson.
| Region | Range | What lives there |
|---|---|---|
| Sub-bass | 20–60 Hz | The rumble you feel more than hear: 808s, sub basses |
| Bass | 60–250 Hz | Kick drum body, bass guitar, the warmth of a mix |
| Low mids | 250–500 Hz | Body of most instruments. Too much sounds "muddy" |
| Mids | 500 Hz–2 kHz | The core of vocals, guitars and snares |
| Upper mids | 2–6 kHz | Presence and clarity. Our ears are most sensitive here |
| Highs ("air") | 6–20 kHz | Cymbals, breath, sparkle |
Amplitude (Loudness)
Amplitude is measured in decibels (dB). Decibels work on a ratio scale:
- +6 dB roughly doubles the signal level.
- +10 dB sounds about twice as loud to most people.
- 1 dB is about the smallest change most people notice.
Inside your DAW, levels are measured in dBFS (decibels relative to full scale). 0 dBFS is the loudest level digital audio can hold, so meters show negative numbers like -12 dBFS. If you go past 0, the audio clips and distorts.
Hearing damage is permanent. Produce at a moderate volume (a level where you could still talk over the music), take a 10-minute break every hour, and turn your volume down before you press play on anything new.
Waveforms & Timbre
A pure sine wave contains only one frequency. Almost every real sound also contains harmonics: quieter frequencies at whole-number multiples of the main note. If the note is 100 Hz, its harmonics sit at 200, 300, 400 Hz and so on. The mix of harmonics creates the timbre.
The four classic waveforms
Go back to the oscillator above. Switch between the waveforms at the same frequency and listen to the timbre change while the pitch stays the same.
A sawtooth has the most harmonics, so it gives a filter the most to work with. That's why most synth sounds start from a saw, as you'll see in Synth Basics.
Phase
Phase is where a wave is in its cycle at a given moment. When two identical waves line up, they add together and get louder. When one is flipped upside down (180° out of phase), they cancel out and you hear silence.
Phase problems are common when you record one source with two microphones, or layer two kick drums. The result sounds thin or hollow. You'll learn to fix this in Recording Instruments and Panning & Stereo.
Humans hear from roughly Hz to Hz.
Doubling a frequency raises the pitch by one .
1. What property of sound do we hear as pitch?
- Amplitude
- Frequency
- Phase
- Timbre
Frequency (measured in Hz) sets the pitch. Amplitude sets the loudness.
2. Which waveform contains every harmonic and sounds the brightest?
- Sine
- Triangle
- Sawtooth
- Square
A sawtooth contains all harmonics (both odd and even), which makes it bright and buzzy.
3. What happens to digital audio above 0 dBFS?
- It gets warmer
- It clips and distorts
- Nothing, it just gets louder
- It turns mono
0 dBFS is the digital ceiling. Anything louder gets cut off ("clipped"), which causes harsh distortion.
4. Two identical waves, one flipped 180°, are played together. What do you hear?
- Twice as loud
- An octave higher
- Silence (they cancel out)
- A chord
That's phase cancellation. The peaks of one wave fill the troughs of the other.