A

A440 (concert pitch)

The international tuning standard: the A above middle C at 440 Hz, codified as ISO 16. Every instrument tuned to it agrees with every other. Hear A440 →

Amplitude

The size of a sound wave's pressure swing - the physical quantity behind loudness. In digital audio it is expressed relative to full scale (dBFS).

B

Binaural beats

A perceived pulsing created by playing slightly different frequencies to each ear; the brain constructs a beat at the difference frequency. Requires headphones. Binaural beats generator →

BPM (beats per minute)

Tempo: how many beats fit in one minute. 60 BPM is one beat per second; one beat lasts 60,000 ÷ BPM milliseconds. BPM to ms calculator →

C

Cent

One hundredth of a semitone - the standard unit for tuning error. Differences under ~5 cents are hard to hear; 100 cents is a full semitone. Note ↔ frequency converter →

Clipping

What happens when a signal tries to go past full scale (0 dBFS): the tops of the waveform are cut flat. Those squared-off peaks add harsh harmonics, which is why clipped audio sounds crackly and distorted. Fix clipped audio (fix.fm) →

Crossover

The frequency at which an audio system hands off between drivers - e.g. sending everything below 80 Hz to a subwoofer and the rest to the main speakers. Subwoofer test →

D

dBFS

Decibels relative to digital full scale. The loudest representable sample is 0 dBFS; every real signal is negative. A peak measure, not a loudness measure.

dBu / dBV

Absolute voltage levels: dBV referenced to 1 V, dBu to 0.7746 V. Pro line level is +4 dBu; consumer line level is −10 dBV. dB converter →

Decibel (dB)

A logarithmic ratio unit used throughout audio. +6 dB doubles voltage, +3 dB doubles power, and roughly +10 dB doubles perceived loudness. dB converter →

E

Equal temperament

The modern tuning system dividing the octave into 12 equal ratios of 2^(1/12), letting every key sound equally in (and equally slightly out of) tune.

F

Frequency

How many times per second a wave repeats, measured in hertz. Higher frequency = higher pitch. Human hearing spans roughly 20 Hz to 20,000 Hz. Tone generator →

Frequency response

How evenly a device reproduces different frequencies, usually shown as a curve. A flat response reproduces all frequencies at equal level. Sweep generator →

Fundamental

The lowest frequency component of a musical sound - the one that names its pitch. Everything above it is harmonics.

H

Harmonics (overtones)

Frequency components at whole-number multiples of the fundamental. Their relative strengths create timbre - why a violin and flute playing the same note sound different. Waveforms guide →

Headroom

The margin between a signal's peak and the maximum the system can pass without clipping. Digital masters typically leave at least 1 dB of true-peak headroom.

Hertz (Hz)

The unit of frequency: cycles per second. Named after Heinrich Hertz. 1 kHz = 1,000 Hz.

I

Interval

The pitch distance between two notes, named by scale steps (minor third, perfect fifth). Recognizing intervals by ear is the core of relative pitch. Interval trainer →

L

Latency

The delay between an audio signal being sent and heard. Bluetooth adds 40-300 ms depending on codec; wired audio is near-instant. Latency test →

LFE

Low-Frequency Effects - the ".1" channel in surround sound, band-limited to roughly 20-120 Hz and reproduced by the subwoofer. Surround sound test →

LUFS

Loudness Units relative to Full Scale - standardized perceived loudness, measured with ear-weighted filtering over time. What streaming platforms normalize on. Streaming loudness guide →

M

Masking

One sound making another inaudible. Steady broadband noise masks unpredictable sounds - the mechanism behind every sleep-noise machine. White noise →

N

Noise colors

Broadband noise named by spectral tilt: white (flat), pink (−3 dB/octave), brown (−6 dB/octave), plus descriptive colors like green (mid-band) and gray (equal-loudness). Noise generator →

Noise floor

The constant background level under the signal: hiss, fans, hum and room tone. Anything quieter than it is buried, so a lower noise floor means a cleaner recording. Remove background noise (fix.fm) →

O

Octave

The interval between a frequency and its double. 220 Hz, 440 Hz, and 880 Hz are the same note (A) in adjacent octaves.

Oscillator

A circuit or algorithm producing a repeating waveform at a set frequency - the sound source inside every synthesizer and every tool on this site. Tone generator →

P

Phase / polarity

Phase is a waveform's position in its cycle; polarity is whether the signal is flipped upside down. Inverted polarity between stereo channels cancels bass and blurs imaging. Phase test →

Pink noise

Noise with equal energy per octave (−3 dB per octave tilt) - sounds balanced to human ears and is the standard signal for speaker calibration. Pink noise →

Pitch

The perceived highness or lowness of a sound - the perceptual counterpart of frequency, mostly determined by the fundamental.

Presbycusis

Age-related hearing loss, starting at the highest frequencies. The reason your ceiling frequency falls predictably with age. Hearing age test →

R

Resonance

A system's tendency to vibrate strongly at particular frequencies. Rooms, speaker cabinets, and instrument bodies all resonate - sometimes helpfully, sometimes not.

Reverb

The reflections that build up and keep sounding after a sound stops, as it bounces off walls, floor and ceiling. A little adds space; too much in a recording is the "big empty room" sound that blurs speech. Remove echo from a recording (fix.fm) →

RMS

Root mean square - the effective average level of a signal, far closer to perceived loudness than peak level. Line-level voltages are specified as RMS.

Room mode

A standing wave between parallel room surfaces that boosts or cancels specific bass frequencies depending on where you sit. The dominant acoustic problem in small rooms. Room mode calculator →

S

Sample rate

How many times per second digital audio measures the waveform. 44.1 kHz (CD) captures everything up to ~22 kHz - the full range of human hearing.

Semitone

The smallest step in Western music - one twelfth of an octave, a frequency ratio of 2^(1/12) ≈ 1.059. Adjacent piano keys are a semitone apart. Transpose calculator →

Sine wave

The purest waveform: a single frequency with no harmonics. The building block all other sounds decompose into, and the standard test signal. Tone generator →

SPL (sound pressure level)

Loudness in the air, in dB referenced to the threshold of hearing (20 µPa). Conversation ≈ 60 dB SPL; hearing damage risk begins around 85 dB for sustained exposure. Decibel meter →

Standing wave

A wave pattern that stays in place because reflections reinforce it - the physics behind room modes and the resonance of instrument strings and pipes.

Sweep

A tone that glides continuously through a frequency range - the fastest way to find dropouts, resonances, and rattles in a speaker or room. Sweep generator →

T

Timbre

The character that distinguishes two sounds of identical pitch and loudness - determined by harmonic content and how the sound evolves over time.

Tinnitus

Sound perceived without an external source, usually ringing or hissing, often linked to hearing damage. Broadband noise is a common masking aid. Tinnitus relief guide →

Transient

The brief, sharp onset of a sound - a drum hit's attack, a consonant. Transients carry rhythm and clarity and are the first casualty of over-compression.

True peak (dBTP)

The estimated analog peak between digital samples after reconstruction. Streaming platforms ask for −1 dBTP ceilings so lossy encoding doesn't clip. Streaming loudness guide →

W

Waveform

The shape of a sound wave over one cycle - sine, square, sawtooth, triangle being the classic four, each with a distinct harmonic recipe and timbre. Waveforms guide →

Wavelength

The physical length of one wave cycle in air: speed of sound (343 m/s) divided by frequency. A 20 Hz wave is 17 m long; a 20 kHz wave is 17 mm.

White noise

Noise with equal power at every frequency - the audio analogue of white light. Sounds bright and hissy because most of its power sits in the top octaves. White noise →