Loudness

Loudness Authority

Our CTO for Broadcast & Production, Thomas Lund, has taken a number of mobile devices, including Apple's iPhone and iPad, to the test bench at the 'TC Lab'.

In this white paper, all the test results, recommendations and a practical guide are disclosed.
 

  • Target-Level for Mobile Recommendation
  • 3-Step Guide: From HD Audio to Mobile
  • Elaboration on Perception, Clarity and Speech Intelligibility

 

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In the Press

There's a reason that world-leading broadcast magazine regularly invite us to share our knowledge: we've been pioneers in the digital audio world since 1985.

We've taken part in research studies and the definition of international broadcast standards right from the start, donating technology which has become a crucial part in new, open international standards.

 

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Loudness Glossary

ATSC A/85

Recommended practices for Digital Television in the US. A/85 is rooted in BS.1770 Loudness and True-peak level. It specifies an anchor based or a universal approach to audio normalization without a clear distinction of when to use what. A/85 includes extensive information about calibrated monitoring environments and may function somewhat like a Dolby manual. Unlike EBU R128, A/85 is only focused on the digital television platform and on the AC3 codec. Published Nov. 2009.

Loudness

A perceptual property of sound. Humans rate loudness between quiet and loud. Several physical and psychological factors contribute to the sensation of loudness. An example of a listening experiment to investigate this property is described in Skovenborg, Quesnell & Nielsen, "Loudness Assessment of Music and Speech", AES 116 convention paper. Note: Loudness does not refer to the switch on a hi-fi which changes the frequency response as the gain ("volume" control) of the system is varied.

BS.1770

See ITU-R BS.1770

Loudness Range

A standardized measure of a the loudness range of a program or a music track. Loudness Range, abbreviated LRA, is based on BS.1770 and part of EBU R128. Loudness Range is measured in units of LU and basically measures the distance between soft and loud parts of the program. The measure is used as a production guideline, for QC manually or on a server, and for checking the integrity of an entire signal-path. The number stays the same downstream of production, even if a program is normalized. Note: Loudness Range replaces a TC Electronic descriptor, "Consistency", used in first generation of its LM5 meters.

Calibrated Monitoring

Studio speakers may be calibrated to produce a specific SPL at a specific location in a specific room. Calibrated monitoring is of benefit to the production of quality audio, and makes moving of a project between studios less complicated. Calibrated monitoring is an advantage to keep loudness under control by ear (as well as by loudness meter), but also to achieve a consistent spectral balance from program to program. When monitoring level is undefined, the level-dependent sensitivity of our ears is allowed to play a role in mixing. With broadcast loudness now standardized, the time is perfect to encourage calibrated monitoring widely. ATSC A/85 includes a discerning chapter about this issue.

LRA

Abbreviation of Loudness Range.

Center of Gravity

Universal program loudness measurement, available in TC loudness meters. Center of Gravity ("CoG") is based on BS.1770 and pioneered the relative-threshold measurement gate. CoG only disregards silence, whereas EBU Loudness focuses on foreground sound. The BS.1770 measure originally didn't have a measurement gate at all, making it susceptible to operator mistakes. CoG may be regarded as an application-friendly update of BS.1770. When a raw BS.1770 measurement is performed by an alert operator to start and stop the measurement, the numbers produced would basically be the same as with CoG. For more information, see Skovenborg & Lund, "Loudness Descriptors to Characterize Programs and Music Tracks", AES 125 convention paper.

LU

The unit of loudness on a relative scale. 1 LU is equivalent to 1 dB. It may also be used to measure Program Loudness, if a Target Level has been defined a zero point on the LUFS scale, for instance 0 LU = -23 LUFS.

CRC

Communications Research Centre. Federal R&D facility in Canada and driving force behind the studies and listening experiments underlying ITU-R BS.1770.

LUFS

The unit of loudness level of a digital signal on an absolute scale. 1 LUFS is equivalent to 1 dB. Most levels in broadcast are in the -36 to -18 LUFS range, while level closer to 0 LUFS would signify very loud.

Codec

A combined structure consisting of an encoder and a decoder. Data-reduction systems such as AAC, MP3, and AC3 are examples of audio codecs.

Max Loudness

The maximum loudness level measured when a sliding window is applied from the beginning to the end of a program. In EBU R128, the width of the sliding window is defined at 400 ms or 3 sec. Max Loudness may be used as a second line of defense against annoyingly loud commercials, should producers start dodging the average approach to loudness that comes with EBU Program Loudness normalization.

dB

The abbreviation of decibel. The dB is employed to express a logarithmic ratio between, for instance, two amplitude levels. In this case, a ratio of 10:1 is the same as 20 dB while 1:10 = 10% is -20 dB. Thereby, dB by nature is always relative. There is no such thing as a level of +3 dB, while a gain of +3 dB is applicable. Sometimes the relative nature of dB is implied, for instance if sound pressure level (SPL) is expressed merely in "dB". Since hearing is a logarithmic sense, gain, distortion, signal/noise and other relationships in audio are typically expressed in dB rather than in percent.

Metadata

Extra data about core data. Core data could be the actual audio, video or text content while metadata may hold the tools necessary to access or understand core data. Metadata is widely used to lock out other vendors from dealing with core data, for instance in word processing, and should therefore only be embraced when based on open standards. The AES/EBU audio interface includes open standard metadata, while AC3 contains certain Dolby specific metadata. In such cases, one goal is to minimize dependency of these elusive extra data.

dBFS

An absolute unit used to describe the sample level in the digital domain. 0 dBFS, where "FS" stands for Full Scale, denotes the maximum encoding value for a sample. Measurements of level specified in dBFS typically indicate sample peak level or true peak level.

Momentary Loudness

The measurement of loudness using a 400 ms sliding window, defined in EBU R128. Momentary loudness should be available for real-time display of loudness on EBU Mode meters. Momentary Loudness yields the fastest and most dynamic display of loudness level.

dBTP

Refers to dBFS true-peak level.

Normalization

Applying a static gain offset to a source, a program or a music track to fulfill certain criteria. Normalization may be based on a variety of criteria, for instance a specific definition of loudness or peak level. Loudness normalization at the station, real-time or file-based, is an advantage to all broadcast platforms.

dBu

An absolute unit used to describe the level of an analog signal. The reference point, 0 dBu, equals 0.775 V RMS.

OP-59

Operational practice by FreeTV, Australia. OP-59 is rooted in BS.1770 Loudness and True-peak level and recommends a speech based as well as a universal approach to audio normalization. All short form programs should be measured using the universal (full mix) method.

Dialnorm

The name of a metadata field in AC3, indicating the average or anchor level of a program. In the AC3 decoder, dialnorm may be used to normalize programs by applying a gain offset and also acts as reference point for the DRC system. Despite its name, dialnorm has no speech-specific use in the decoder. The Target level of a broadcast station is normally used as its dialnorm setting for AC3 based platforms.

Perception

How humans interpret sensory information. Most senses relate to physical stimuli on a logarithmic scale, thereby enabling a large magnitude of stimuli to be perceived. As part of auditory perception, loudness relates to physical stimuli on a logarithmic scale which makes dB useful for measurement.

Dialog Intelligence

A proprietary technology patented by Dolby Labs to discriminate between speech and other sounds, and thereby gate out non-speech portions when measuring loudness. The technique may not be effective at controlling commercials, nor of use across genres where the distinction between speech and non-speech is blurred. Dialog Intelligence ("DI") is ambiguous and not defined in a standard. Dolby audio meters may run different revisions of software where a certain version of DI is combined with various weighting methods. Also see "Universal Measurement".

phon

A unit of perceived loudness level. The phon scale is similar to the SPL dB scale. The two coincide, for 1 kHz tones, at SPL levels above 40 dB. Consequently, a 1 kHz pure tone with an SPL of 50 dB measures 50 phons, and is typically perceived as having double the loudness of 40 phons.

DRC

Dynamic Range Control. May refer to a feature of AC3, capable of restricting dynamic range during reproduction. AC3 DRC does not employ BS.1770 compliant correction capability and is in some products impossible to disable for the end-listener.

P/LOUD

A group of audio professionals within EBU and from everywhere in the world investigating loudness measurement and loudness control in broadcast. P/LOUD is chaired by Florian Camerer of ORF and is a sub-group of EBU's Expert Community on Audio, ECA. One of the outputs of P/LOUD, recommendation EBU R128, was published September 2010, pioneering various new BS.1770 compliant tools and production techniques.

Dolby

Brand name of an American company making business from selling licenses for patented technology in audio and entertainment. In 2005, Dolby Laboratories went public with stocks traded at the New York Stock Exchange.

PPM

Peak Program(me) Meter. Often used about a Quasi-peak Meter.

EBU Program Loudness

Integrated, universal loudness measure applicable to an entire program, film or music track. EBU Program Loudness is based on ITU-R BS.1770, but adds a relative- threshold measurement-gate allowing it to focus on foreground sound. See also Target Level.

Program Loudness

The notion of having one integrated loudness number represent an entire program or music track. EBU Program Loudness and Center of Gravity are such examples. Program loudness may be used to normalize broadcast programs, commercials, music tracks etc. individually.

EBU Mode

Loudness meter specification defined by EBU. Loudness meters compliant with EBU Mode can be relied on to perform measurements accordingly. Operational details such as scales and units are also covered. EBU Mode is defined in EBU Tech 3341.

QPPM

The same as Quasi-peak Meter.

EBU R128

Audio guidelines for broadcast in Europe, rooted in ITU-R BS.1770 Loudness and True-peak level. Compared to ATSC A/85, R128 includes significant new BS.1770 compliant tools that work across genres and across broadcast platforms. R128 is based entirely on open standards, and supported by four Technical Documents specifying EBU Program Loudness, Loudness Range, EBU mode, Short-term Loudness, Momentary Loudness, guidelines etc. The practical guidelines include details about taming commercials transparently, and an extensive distribution section unfolding the benefits of loudness normalization to all broadcast platforms.

Quasi-peak Meter

Display of audio level. The quasi peak meter, PPM or QPPM, has been widely used in broadcast and film. Standardized as IEC 60268-10, the meter is intentionally slowed down in its "attack" response time, and even more in its decay. Arguably, it's neither a peak level nor an average level meter, and also not suitable for measuring loudness level. Higher peaks than what is shown on a QPPM can readily be found in a signal when also measured by a true-peak meter.

EBU Tech 3341

Definition of EBU Mode, a set of requirements for loudness meters, by PLOUD.

Sample-peak Meter

The sample-peak meter is one of the dregs of digital audio. Easy to implement and easy to cheat, it carries the main responsibility for the loudness wars in CD and commercial productions. The sample-peak meter is typically found in workstations and in editing systems, but don't rely on it. In digital audio, use a true-peak meter to display peak level and a loudness meter to determine normalization.

EBU Tech 3342

Definition of Loudness Range, contributed by TC Electronic and standardized by EBU.

Sliding Window

A sliding window provides a method to process only a number of data points at a time. Sliding RMS window measurements are useful in audio, for instance where a property is examined for time variability. Considering loudness, sliding window methodology is particularly useful for live and production applications where there is not yet access to the full data. The sliding window length is therefore specified in EBU R128, and defined as either 400 ms (Momentary Loudness) or 3 sec (Short-term Loudness).

ITU-R BS.1770

Global standard on Broadcast Loudness and True-peak level measurement. The loudness part is based on an leq measurement employing K weighting. This baseline method is relatively simple but has been verified independently. The True-peak part of the standard was specified by AES SC-02-01. BS.1770-1 may be used for measuring mono, stereo and 5.1 content and is up for revision Oct. 2010.

SPL Sound Pressure Level

An acoustic, logarithmic measure relative to a sound pressure of 20 µPa (1 kHz pure tone), which is considered to be the threshold of human hearing. Note: Unlike how dB is otherwise used, this referencepoint is implied when we speak about, for instance, "an SPL of 60 dB". Because the ear's spectral sensitivity depends on SPL, a filter to approximate the ear's sensitivity in a specific SPL range is used when measuring, for instance A or C weighting.

Integrated Loudness

The principle of indicating loudness as one number to specify the overall loudness of an entire program or music track from beginning to end. Examples of Integrated Loudness: Center of Gravity, EBU Program Loudness, "raw" BS.1770 Loudness Level.

Static Metadata

The principle of keeping metadata the same as much as possible in broadcast transmission, thereby limiting the number of things that can go wrong. Stations employing static metadata continuously insert Target Loudness as the program loudness number ("dialnorm" in AC3), and only switch metadata if the format changes, for instance from stereo to 5.1. EBU R128 and ATSC A/85 include descriptions of static metadata broadcast station designs.

K weighting

A frequency weighting developed by the CRC also known as "R2LB".

Target Loudness

Target Loudness is by definition the normalization level of a broadcast station. In EBU R128, Target Loudness is - 23 LUFS for all genres and program types. In ATSC A/85, Target Loudness is -24 LUFS, however measured without the gating of EBU Mode. With calibrated monitoring in place, target loudness is translated to a predictable SPL in production studios. Once a Target Loudness has been defined, users may choose to show loudness measurement on a relative scale (LU) rather than on an absolute scale (LUFS). In a metadata-based delivery system, Target Loudness is the default number to indicate program level. In AC3, the name of this metadata parameter is "dialnorm".

Leq

Equivalent sound level. An energy-integrated measure of sound often combined with a frequency weighting to approximate hearing at a certain sound pressure level. Integration may be over seconds, minutes or hours. The loudness part of BS.1770-1 makes use of a certain frequency weighting, Leq(K), also known as Leq(R2LB), as well as different gain factors for front and rear channels in 5.1.

True-peak Level

An absolute measure used to describe the true-peak level of a digital signal. Can be measured as specified in ITU-R BS.1770. The intrinsic or true-peak level of a digital signal may be 3 or more dB higher than the sample peak level of the same signal. Contrary to sample-peak level, true-peak is a valuable estimate of the headroom required to handle a signal without clipping. 0 dBFS+ level is routinely printed to CDs, leading to distortion in reproduction equipment, sample rate converters and data reduction systems. For more information see Lund, "Stop Counting Samples", AES 121 convention paper.

LFS

The unit of loudness on an absolute scale. The same as LUFS.

True-peak Meter

An improved type of peak level meter for use in digital audio. While the sample-peak meter was sufficient in the early days of digital, it is easy to deceive and not a trustworthy tool anymore.

LKFS

The unit of loudness on an absolute scale. The same as LUFS. EBU has submitted a proposal to ITU-R, documenting how the inclusion of the "K", denoting K-weighting, is out of line with a standardized use of units, and also is inconsistent with LU. EBU therefore recommends the use of "LUFS" instead of "LKFS".

Universal Measurement

The principle of basing a loudness meausure on all sources of a program as opposed to measuring only one, i.e. speech or music. A universal measure based on an open standard is transparent and does not depend on ambiguous discrimination between sources. Examples of universal measurements: EBU Program Loudness, Center of Gravity, Max Loudness and Sliding Window Loudness of EBU R128. Also see "Dialog Intelligence".

Zap Test

The highest jumps in loudness typically occur when "zapping" between different TV channels. The Zap Test is a statistically founded method to examine how the extent of these loudness jumps are affected by applying different normalization schemes. For more information, see Skovenborg & Lund, "Loudness Descriptors to Characterize Wide Loudness Range Material", AES 127 convention paper.