Glossary¶

Loudness¶

An objective measurement of the perceived loudness of an audio signal. The algorithms for this measurement have been studied and designed by the EBU PLOUD Group and described in the EBU R128 Loudness Recommendation.

gating block¶

A sliding window of 400 milliseconds in duration with an overlap of 75% used to take loudness measurements. With the overlap factored in, a new gating block will occur every 100 milliseconds.

Integrated Loudness¶

Loudness measurement of an entire “program” generated using

A 2-stage “K-weighting” pre-filter
Mean-square summation using per-channel weighting
Gating of 400-millisecond blocks with 75% overlap, using an absolute and relative threshold

This algorithm is described in ITU-R BS.1770.

Loudness Unit¶

“Loudness Unit (LU)” is the scale of a loudness measuring device or meter.

The value of an audio signal in loudness units represents the loss or gain dB that is required to bring the signal to 0 LU, e.g. a signal that reads -10 LU will require 10 dB of gain to bring that signal up to a reading of 0 LU.

This is defined in ITU-R BS.1770 (Annex 1) and clarified in EBU Tech 3341 (section 2.5).

LUFS¶

Absolute Loudness Unit (with respect to Full Scale).

This is defined in EBU Tech 3341.

LU¶

Loudness Unit relative to a target level, typically user-defined.

If a target of -23 LUFS is chosen, the measurement of a signal at -23.0 LUFS would be displayed as 0.0 LU.

This is defined in EBU Tech 3341.

Momentary Loudness¶

Loudness measurement generated using the algorithm described for Integrated Loudness, but with a 400 ms sliding integration window and without gating.

This algorithm is described in ITU-R BS.1771.

Short-Term Loudness¶

Loudness measurement generated using the algorithm described for Integrated Loudness, but without gating and with a measurement window of 3 seconds.

This algorithm is described in ITU-R BS.1771

Loudness Range¶

The variation of loudness throughout an entire “program” using a sliding 3-second analysis window and a variation of the gating algorithm for Integrated Loudness. The result is then computed as the difference between the upper 95th and lower 10th percentiles.

This algorithm is described in EBU Tech 3342

True Peak¶

The maximum (positive or negative) value of a waveform in the continuous time domain as opposed to the “sample peaks” typically measured in discrete time. This is calculated by oversampling the signal and applying an interpolating filter as described in ITU-R BS.1770.

block size¶

The number of audio samples per channel processed within one period. This is typically chosen before the audio processing engine starts and remains constant throughout the session.

BS 1770¶

ITU-R BS.1770 is the recommendation specifying methods of filtering, windowing and gating for loudness measurements.

BS 1771¶

ITU-R BS.1771 is the recommendation specifying the requirements for loudness metering. It also defines momentary and short-term loudness calculations.