Number of oscillations per second, in hertz (Hz). Determines perceived pitch — 440 Hz = concert pitch A.

Time for one complete oscillation. T = 1 / f. At 100 Hz, T = 10 ms.

Spatial length of one oscillation in air. λ = c / f. At 100 Hz and 20 °C, λ ≈ 3.43 m.

Speed of sound in air, ≈ 343 m/s at 20 °C. Rises with temperature (~0.6 m/s per °C).

Unit of frequency: 1 Hz = one oscillation per second. kHz = 1000 Hz.

1/1000 of a second. Standard unit for audio delays. Sound travels about 34 cm in 1 ms.

Digital samples. Samples per unit of time depend on the sample rate: 1 ms at 48 kHz = 48 samples.

Sampling rate in Hz. 48 000 Hz means 48 000 samples per second. Standard pro-audio rates: 44.1k / 48k / 88.2k / 96k / 176.4k / 192k.

Difference between two values. Δt = time difference, Δd = distance difference, Δ dB = level difference.

Angular position in the oscillation cycle, 0 – 360°. 180° = inverted, 360° = one full cycle.

Logarithmic ratio unit. +6 dB = 2× voltage, +10 dB ≈ twice as loud perceptually.

Level reference: 0 dBV = 1 volt RMS. Common on consumer gear (−10 dBV).

Level reference: 0 dBu = 0.7746 V RMS (historic 600 Ω reference). Pro-audio standard: +4 dBu = 1.228 V RMS. 0 dBu ≈ −2.2 dBV.

Sound pressure level in dB, referenced to 20 µPa (threshold of hearing). Live concert ca. 100 – 110 dB SPL.

Root mean square — describes continuous power handling / output, more relevant than peak values.

Sound pressure halves with each doubling of distance — i.e. −6 dB per doubling in the free field.

Reserve between nominal and maximum level. Critical so peaks don't clip.

Two signals with identical content and identical phase. Add linearly (voltage sum) — two equal signals produce +6 dB.

Unit of electrical power. Amplifier and loudspeaker handling typically stated in W RMS.

Filter selectivity. Higher Q = narrower bandwidth of a bell-type EQ filter. Q 1 ≈ 1.4 octaves, Q 10 ≈ 0.14 octaves.

Frequency range, often stated in octaves. BW = log₂(f_high / f_low).

Frequency-response adjustment. Boost or cut in a defined band.

One octave up = double the frequency, one octave down = half the frequency.

Alternating cancellations and peaks in the frequency response caused by a time offset between two correlated signals (e.g. two mics or two speakers).

Frequency at which two signals interfere destructively — level drop in the frequency response.

Frequency at which two signals sum constructively — level peak in the frequency response.

Current position in the cycle, in degrees (0 – 360°). 180° equals polarity inversion.

Phase angle expressed as a time delay. Frequency-dependent: the same angle corresponds to different times at different frequencies.

Tempo in beats per minute. ¼ note [ms] = 60 000 / BPM.

Video frame rate. Standards: 24 (cinema), 25 (PAL), 29.97/30 (NTSC), 50/60 (sports/HFR).

One image in a video sequence. At 25 fps, one frame lasts 40 ms.

2-beat duration. At 120 BPM = 1 000 ms.

1 beat — reference note for BPM. At 120 BPM = 500 ms.

½ beat. At 120 BPM = 250 ms.

1.5× the normal duration (eighth + sixteenth). At 120 BPM = 375 ms. Popular for dub delays.

3 equal notes in the time of 2 regular ones. ⅛ triplet = 3 in one beat. At 120 BPM an ⅛ triplet ≈ 167 ms.

Same frequency, no interval.

Minor = 1 semitone (tension), major = 2 semitones (diatonic).

Minor = 3 ST (minor character), major = 4 ST (major character). ⅓ octave = exactly a major third.

Frequency ratio ≈ 1.335. Consonant, often a resolution interval.

Exactly half an octave. Historically «diabolus in musica» — very dissonant.

Frequency ratio ≈ 1.498 (≈ 3:2). Most important harmonic interval — defines keys.

Minor = 8 ST, major = 9 ST. ⅔ octave = exactly a minor sixth.

Minor = 10 ST (dominant seventh), major = 11 ST (leading-tone tension).

Frequency doubling. Strongest sense of consonance. Note name repeats.

Compound of an octave + a smaller interval: 9th = octave + 2nd, 10th = octave + 3rd, 11th = octave + 4th, 12th = octave + 5th, etc.

Public-address system for live sound reinforcement — mixer, amplifiers, loudspeakers.

Main mix position in the room — where the engineer stands to mix for the audience.

Throw distance vs. half the coverage width. FAR = 1 / sin(°/2). 90° → FAR 1.41, 60° → FAR 2.

Lateral ratio: LAR = 2 / FAR. Tells how far apart speakers can be placed for a given throw distance.

Dispersion angle of a loudspeaker, usually measured between the −6 dB points.

Distance over which a speaker stays usably loud.

Angle between two adjacent boxes in a coupled line / line array.

Driver for high frequencies (typically > 2 kHz). Mounted at the top of the enclosure.

Low-frequency driver for the lowest band (typically < 100 Hz). Usually floor-placed.

Low / mid / high frequency range. Typical boundaries: LF < 250 Hz, MF 250–4 k, HF > 4 k.

Filter splitting the signal into bands — typically between sub and top, or between LF/HF in multi-way boxes.

Additional speaker position farther back in the audience, electrically delayed to time-align with the main system. Rule of thumb: needed above Δt > 40 ms.

Two subs in line — the rear one electrically delayed. Creates cancellation behind the stack, protecting the stage from sub energy.

Multiple subs in line with progressive forward delay — focuses energy in the throw direction.

Sub configuration with a cardioid radiation pattern — loud forward, quiet rearward.

Narrow, very loud zone along the centerline between two subs placed too far apart. Caused by constructive summation — with cancellations on the sides.

d_max = c / (2 × XOVR) = ½ wavelength at the crossover frequency. Prevents power alleys.

Unit of electrical resistance / impedance. kΩ = 1 000 Ω, MΩ = 1 000 000 Ω, mΩ = 1/1000 Ω.

High impedance. Typical for instrument inputs (≥ 1 MΩ) — e.g. electric guitar, bass pickups.

Low impedance. Standard for microphones (200 – 600 Ω) and line signals.

Very low level: −60 to −40 dBV (1 – 10 mV RMS). Requires pre-amplification.

Pro-audio line level: +4 dBu = 1.228 V RMS. Balanced, typically via XLR or TRS.

Consumer line level: −10 dBV = 316 mV RMS. Common on HiFi gear via RCA, unbalanced.

+20 to +40 dBV (10 – 100 V RMS) from a very low source impedance (< 100 mΩ). Speaker input: 4 – 16 Ω.