Loudness metering

Loudness ITU-R BS 1770 &amp EBU R128 PLOUD

ITU-R BS.1170-4 and EBU R128 recommendations introduce a new paradigm for audio metering, which define a way to measure perceived loudness of audio material in a normalized and reproducible manner.

Please refer to the official documents freely available online at tech.ebu.ch/groups/ploud * or consult a reference book such as “Audio Metering. Measurements, standards and practice” by Eddy Brixen (Focal Press, ISBN 9780240814674) for detailed information on this subject.

Principles

Units

ITU-R BS.1170-2 notably defines LU (Loudness Unit) and LUFS (Loudness Unit, referenced to Full Scale) units, which are used by EBU R128, and Maximum True Peak Level.

  • LU is used for measurements relative to a reference level and measuring range.

  • LUFS is used for absolute measurements.

The meter display is switchable between LUFS (absolute, default) and LU (relative). The target loudness level to aim for is -23 LUFS = 0 LU.

Loudness and EBU mode

EBU mode specifies three time scales corresponding to three different, complementary loudness levels

  • M: Momentary, 400ms integration time
  • S: Short-term, 3s integration time
  • I: Integrated from start of measurement or last reset, gated
Note

Loudness is a measure of global loudness, so individual channel metering is not relevant in this context.

No additional slowdown of the attack or release of the meter is employed, as indicated by the norm.

The integrated loudness can be understood as the overload loudness of the audio over time, excluding very soft passages through the use of absolute and relative gating.

Loudness Range (LRA)

Loudness range measures the average long-term variations of the loudness; it is expressed in LU.

Scales

EBU R128 specifies two normalized scales:

  • EBU +9, ranging from -18.0 LU to +9.0 LU (-41.0 LUFS to -14.0 LUFS)
  • EBU +18, ranging from -36.0 LU to +18.0 LU (-59.0 LUFS to -5.0 LUFS) (Default)

Dolby Dialogue Intelligence

Introduction

While EBU R128 aims to measure global perceived loudness, irrespectively of the audio material, Dolby Dialogue Intelligence is a patented technology designed to specifically measure the perceived loudness of dialogue elements in the audio. It is therefore targeted towards broadcast applications.

General principle

Dialogue Intelligence replaces EBU R128’s level-based gate with a speech-content ratio based gate. The algorithm computes several low-level features for the incoming signal in speech channels. These are then combined into an overall speech percentage figure. When speech content is detected, Integrated Loudness is computed from the speech channels which have a speech content ratio above a certain threshold.

When other material is detected, i.e. not speech, standard EBU R128 Integrated Loudness computation is employed.

Display

The current speech content is displayed as text below the current gate status.

Additionally, color coding indicates the speech content ratio.

  • Speech : speech content present

  • Green: high speech content

  • Orange: medium speech content

  • Red: low speech content

  • Other: other material present

Delay and compensation

The sophistication of the algorithms employed in Dialogue Intelligence incurs an overall latency of 2048ms (approx. 2s).

When Dialogue Intelligence is enabled, the display of other Loudness values is compensated to make sure meter readings are consistent. Other real-time meter (RMS, TruePeak) displays are not compensated, as we feel in this case maintaining the best reactivity to the incoming signal is more important.

All meter statistics are time-aligned.

Surround

Channels taken into account by the algorithm are determined based on the current channel configuration.

For mono/stereo signals, all channels are taken into account. For surround configurations, only Left/Right and Center channels are taken into account, if present.

Note

Dialogue Intelligence computation only affects I (Integrated) Loudness values.

Toggling Dialogue Intelligence on and off forces a reset of the meter values.

Controls and display

Display

The meter display has the following arrangement

  • left bar: Momentary Loudness value

  • right bar: Short-term Loudness

  • text overlay: Integrated Loudness and Loudness Range (LU) values, Gated indicator lights red when gate is active

The Loudness Range value is displayed once measurement has been running for at least 60 seconds, according to the EBU Tech 3342 specification, otherwise a ‘LRA Unstable’ warning is shown.

Pause

Clicking the button pauses measurement; clicking again resumes it. This allows you to make adjustments without affecting Integrated Loudness, instead of having to start all over again.

Reset

Clicking the button resets the meter to its initial state.

Note

Don’t forget to reset the Loudness meter if you’re starting playback of a new track, as Integrated Loudness, by design, measures the overall Loudness since the last reset.

Otherwise you’d be measuring the overall Loudness of the combined tracks, which is probably not what you want.

Setup

EBU R128 Loudness metering setup.

Presets

Custom

Uses user-defined custom range according to min./max. values below.

Default

Sets the meter to the recommended scale (EBU +18 LUFS).

EBU +9 LU

Sets the meter to use EBU +9 scale in LU units.

EBU

+9 LUFS Sets the meter to use EBU +9 scale in LUFS units.

EBU +18

LU Sets the meter to use EBU +18 scale in LU units.

EBU +18 LUFS

Sets the meter to use EBU +18 scale in LUFS units.

-23 LUFS Long program

CST specification

Sets the meter to use EBU +18 scale in LUFS units with reference @ -23 LUFS and color split @-/+ 7LU from the reference.

-23 LUFS Short program

CST specification

Sets the meter to use EBU +18 scale in LUFS units with reference @ -23 LUFS and Max defined 3LU up to the reference.

Dolby Dialogue Intelligence

Dolby Dialogue Intelligence (TM)

Toggles usage of Dolby Dialogue Intelligence speech gate.

Speech threshold

Defines the speech content threshold in %. Speech channels with a speech content ratio below this value do not participate in the Loudness computation.

Range

Min.

Minimum Loudness to display on the bar-graphs. User adjustable.

Max.

Maximum Loudness to display on the bar-graphs. User adjustable.

Scale / split

Scale

Meter labels are defined here as a comma separated list of dB values to be shown on the side of the meters. This also defines where to the corresponding horizontal markings. Default is -72;-40;-18;-9;-6;-3;-1;0;1;3.

Colors

This lets you customize the values at which color transitions occur. You can enter as many values as you wish, as a comma separated list, but make sure the values are in increasing order. Default is -9;0.

The last value always defines the clip level, which will be indicated in red.

Other

Controls whether meters are drawn with texture or in a plain solid color. Default is on.