Loudness Descriptors for use inProduction and Broadcast

T h o m a s L u n d

T C E l e c t r o n i c A / SD e n m a r k

V D T S y m p o s i u m • H o h e n k a m m e r • N o v 1 , 2 0 0 9

A number to measure certain aspects of an entire program or music track.

As simple as possible, but no simpler.

Definition

Audio Descriptor

Peak LevelNormalization

Low dynamic range material end up loud when level control is based only on a peak level measure.

That’s what

happened to CD and

Commercials on TV.

Audio LevelHeadroom is needed several places in the signal-path:

• DA Converters• Filters, analog and digital• Sample rate converters• Data reduction codecs (e.g. MP3)

0 dBFS+ level is hit more and more frequently on new pop/rock releases.

Critical Areas

Sample Rate Conversion

fs/8 sine at +0.7 dBFS through SRC

Listening example:

Don’t Stop, Anastacia

Original CD, normal stereo

Remember how loud this track is in order tocompare against distortion level in the next examples.

0 dBFS+

Same song, NAD512 CD player, listening here

0 dBFS+

CD Production“Desktop Audio” Clipping and bad limiting can create a

lot of alias distortion

Clipping may happen- on the mix buss of a DAW- in plug-in interface and processing- imported from sample libraries

and may not be seen or heard

DDD is not a sign of quality

Data Reduction

Beethoven, Kliegel & TichmanM component example

Notice more cello than piano and room

M/S Listening

Notice more piano and room than cello

Beethoven, Kliegel & TichmanS component example

M/S Listening

iTunes Codec Listening

Beethoven, Kliegel & TichmanS component exampleListen after data reductionAAC 128 kbps

Notice compromised sense of space, and warbling artifacts

Data Reduction

Two Fronts AAC is our best codec, but@128kbps it’s not transparent.

The combination with hyper-level is even worse...

Daniel Powter, “Bad Day”S component exampleNo data reduction

iTunes Codec Listening

Daniel Powter, “Bad Day”S component exampleListen after data reduction (6 dB pre-attenuation)AAC 128 kbps

iTunes Codec Listening

Note glitches and “tick” sounds when codec overloads

Daniel Powter, “Bad Day”S component exampleListen after data reduction (no pre-attenuation)AAC 128 kbps

iTunes Codec Listening

Just Gettin’ AroundS component exampleListen after data reduction (no pre-attenuation)AAC 256 kbps

iTunes Codec Listening

Data Reduction

Is it really necessary?

Bandwidth is going up. Don’t risk future compatibility and audio quality.

Data reducing pop music without attenuation leads to distortion in radio station archives.

LoudnessUnlike Level, Loudness is subjective. Listeners weigh a number of factors differently:

Variability between listeners: BLV (Age, Culture, Gender etc.)Variability within the same listener: WLV (Mood, Focus etc.)Variability because of reproduction. System, average SPL etc.

A Loudness measure must be based on statistics.

=> Extensive listening tests together with McGill University.

- Sound Pressure Level- Frequency Contents- Duration

Loudness

A standardized way of measuring

- loudness and- true-peak level

for mono, stereo and 5.1 content

New ITUStandard

ITU-R BS.1770

Leq Weighting

R2LB

CalibrationITU-R BS.1770 defines loudness dose for mono, stereo and 5.1

-20 dBFS

Sine, 1 kHz

Summing of channels emulates acoustic speaker summing

-23 LUFS

CalibrationITU-R BS.1770 defines loudness dose for mono, stereo and 5.1

-20 dBFS

-20 LUFS

Sine, 1 kHz

-20 dBFS

Summing of channels emulates acoustic speaker summing

CalibrationITU-R BS.1770 defines loudness dose for mono, stereo and 5.1

-20 dBFS

-15.3 LFS

Sine, 1 kHz

-20 dBFS

-20 dBFS

-20 dBFS

-20 dBFS

Summing of channels emulates acoustic speaker summing

Realtime MeteringInstant Loudness and PeakLoudness History

Production (mixing) Live balancingRealtime intervention

Derived from the open and verified BS.1770 standard:

Universal Descriptors

Engineers and journalists need to see the consumer loudness range tolerance

Universal DescriptorsCenter of GravityConsistency

Delivery SpecificationLevel off-setLogging purposes

Universal Descriptors

Realtime MeteringInstant Loudness and PeakLoudness History

Production (mixing) Live balancingRealtime intervention

Engineers and journalists need to see the consumer loudness range tolerance

A single descriptor is not sufficient, when comparing across genres.

Derived from the open and verified BS.1770 standard:

Universal Descriptors

Indicates the overall loudness of a program or a music track.

Not just for dialog, but for any content.

Center of GravityUnit: LKFS

Universal Descriptors

Center of Gravity

Center of Gravity Target

Measures -28 LKFSTarget is -20 LKFS

Directly operational for gain offsets.

Compatible with“dialnorm” in AC3.

Center of Gravity

Moved to Target

Gain offset +8 dBDirectly operational for gain offsets.

Compatible with“dialnorm” in AC3.

Indicates the overall loudness of a program or a music track.

Not just for dialog, but for any content.

Center of Gravity

Indicates the loudness changes inside a program or a track.

Consistency is an objective measureof Loudness Range.

“0” is at the top of the scale, and signifies a steady signal, e.g. a tone.

Consistency

Unit: LKFS

Unit: LU

Universal Descriptors

ConsistencyMeasures a program’s

Loudness Range.

Example:Consistency = -5 LU

To keep a constant

loudness during the

program, a +- 5 dB

fader gain ride would

be required.

Loudness Range =

Consistency x 2

Fader ride

ConsistencyMeasures a program’s

Loudness Range.

Example:Consistency = -5 LU

To keep a constant

loudness during the

program, a +- 5 dB

fader gain ride would

be required.

Loudness Range =

Consistency x 2

Fader ride

ConsistencyMeasures a program’s

Loudness Range.

Example:Consistency = -5 LU

To keep a constant

loudness during the

program, a +- 5 dB

fader gain ride would

be required.

Loudness Range =

Consistency x 2

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BroadcastPrograms

1300 samples from

different countries

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Commercialor Promos

2000 samples from

different countries

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Movies

52 samples,

mostly Hollywood

Details:

AES125 paper,

San Francisco,

Oct., 2008.

Low Level

Good Thing, Ry Cooder Hotel California, Eagles

Good

Dirty Blvd, Lou Reed Come With Me, B. Raitt

Bad

Corazon Espinado, Santana Bittersweet Symph, Verve

Ugly

Since U Been Gone, K Clarkson Tomorrow Never Comes, Metallica

Ravel,Bolero

Directly off CD.

Max peak level:

-0.3 dBFS.

ReferencesZwicker & Fastl, 1990Psychoacoustics - Facts and Models

Moore et al. December 2003 (JAES no 12)Why are Commercials so Loud?

Skovenborg & Nielsen, 2004 (AES 117)Evaluation of Loudness Models with Music and Speech

Nielsen & Lund, 1999 - 2006 (AES 23, 107, 109, 111, 121)0 dBFS+ Level in Mastering and Audio Production

Skovenborg & Lund, 2008 (AES 125)Loudness Descriptors to CharacterizePrograms and Music Tracks

Thomas LundTC Electronic A/SRisskov, Denmark

ContinuedReading

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