Skip to content

Glossary of technical terms

The analysis uses some technical audio measures. Here is what they mean in plain language:

LUFS (Loudness Units relative to Full Scale)

A standard measure of how loud a recording sounds to the human ear.

  • More negative values (e.g. –23 LUFS) = quieter.
  • Less negative values (e.g. –12 LUFS) = louder.

LUFS is different from raw signal level because it models human perception, not just peak amplitude.

RMS (Root Mean Square energy)

A mathematical average of the audio signal’s energy.

  • Higher RMS = consistently louder audio.
  • Lower RMS = softer audio.

Unlike LUFS, RMS is not perceptually weighted (it is less affected by short spikes or silence), but it still gives a good idea of “overall power”.

Spectral centroid

Indicates where the “centre of mass” of the spectrum lies.

  • Higher values = brighter sound (more treble).
  • Lower values = darker sound (more bass).

Think of it as a rough proxy for how “bright” or “dull” a recording sounds.

MFCC (Mel-frequency cepstral coefficients)

A set of numerical values that describe the timbre — the tone colour or texture — of a sound. They are widely used in speech and music analysis to compare how similar different recordings sound. In the analyse_song tool, MFCCs are averaged and compared using cosine similarity to estimate overall sound closeness.

Stereo correlation (L/R correlation)

Measures how similar the left and right channels are.

  • 1.0 = channels are identical (mono).
  • 0.0 = completely different (maximal stereo).

Negative values (rare in music) = channels are inverted relative to each other.

Pitch (measured in cents)

1 semitone = 100 cents.

  • +10 cents = slightly sharp (higher than reference).
  • –10 cents = slightly flat (lower than reference).

Useful for detecting tape speed differences or detuned transfers.

Duration ratio

Compares the running time of a version to a reference.

  • 1.0 = same duration.
  • >1.0 = version is longer.
  • <1.0 = version is shorter.

Can reveal edits or speed differences.

Why these measures matter

Together, these metrics give a multi-dimensional view of a recording:

  • LUFS and RMS → how loud or powerful it sounds.
  • Spectral centroid → how bright or dark it is.
  • MFCC similarity → how close two versions “feel” in timbre.
  • Stereo metrics → whether the mix is centred or imbalanced.
  • Pitch/Duration → whether a transfer was sped up, slowed down, or detuned.