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Visualising sound 11
Audio loudness metering

Level of challenge Intermediate


Welcome to this tutorial on loudness and metering.


Loudness is closely related to amplitude and volume, and an important consideration when mixing and mastering finished music and dialogue. Unlike volume, which describes amplitude at a moment in time, perceived loudness is about how we experience volume over time. Loudness is therefore about perceptions of average volume or level.


Caption - Historical loudness problems

In recent years there has been much concern about sound engineering work practices relating to loudness where marketing is an important factor in decision making. Advertisers and record companies have been pre-occupied with attempting to make their recordings louder than their competitors. Because peak level restrictions are imposed by recording, playback and broadcasting technologies, they have tried to use narrow dynamic range and peak level maximisation to increase perceived loudness.


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Caption - Dynamic range compression

The primary tools to achieve this are compression and limiting and the practise is therefore often referred to as dynamic range compression.


There are 4 primary problems with these work practices ..


Caption - Problem 1 - Loudness differences between programme material

Firstly, other content creators such as film makers, television programme makers, and classical music record companies favour recordings with a wide dynamic range, which means their products have much lower average loudness levels. This means that listeners must constantly re-adjust volume level when switching between recordings or when watching programme material such as films and documentaries which are interrupted with commercial breaks.


When different types of audio content, such as music, commercials, films and news are combined in a channel, there can be wide variations in loudness. This is because different creators have different objectives. Commercial makers adhere to so called interruption marketing practices, whereby commercials are mixed and mastered as loud as possible in order to grab attention. Feature films on the other hand, exploit wide contrasts in dynamics for dramatic effect. Broadcast them side by side and you have uncomfortable changes in loudness. The same is true for music broadcasting or even listening to a playlist you have created on your smart-phone.


Caption - Problem 2 - Listener fatigue

Secondly, recordings with narrow dynamic range and which have been peak level maximised can be very fatiguing to listen to.


Caption - Problem 3 - Distortion

Thirdly, many of the loudness maximisation work practices produce very distorted finished products which spoil not only the nuances of dynamics but the harmonic content of the sounds themselves.


Caption - Problem 4 - Inappropriate loudness

And lastly, if a programme of tracks, such as an album, contains both aggressive compositions and ballads, then the ballads can end up sounding disproportionately loud.


There has therefore been a movement towards defining some universal standards for measuring and metering loudness, and defining agreed loudness levels for recordings.


Caption - Loudness correction during playback

Before we examine the implications of loudness metering for project studio owners, lets look at what happens when different types of content are processed by a broadcaster either before or during broadcast or playback, to ensure a more consistent loudness experience for the listener.


Broadcasters and playback technologies are increasingly introducing methods of correcting loudness differences during playback. Examples include TC Electronics range of real time loudness processors and Apples sound check algorithm for iTunes. After being subject to loudness correction, any content that has been heavily processed during mastering to be loud all the time, now sounds quieter, duller and less interesting than the content which has maintained its dynamics.


If playback technologies and broadcasters adopt the new loudness and metering standards, and they are, there will be little point in content creators trying to make their content louder, and they too will have to adopt the same loudness metering standards during mixing and mastering.


So lets look next, at what we can do to ensure our recordings conform to new loudness standards, and will not be subject to loudness correction, or even rejection, by broadcasters.


Caption - Metering

In the past, the studio engineer has relied on 2 technologies for looking at volume level, peak programme level meters, and VU, or Volume Unit, meters.


Caption - Peak programme level meters

Peak programme level meters, or PPM meters, display the peak level of signals in audio equipment. There are many types of PPM and they all help the studio engineer determine the peak levels in a soundwave signal.


One type of PPM is the True Peak Programme Meter which displays the changing peak level of a soundwave signal. They are used to identify the loudest peak in a signal.


Another type are Sample Peak Programme Meters, also sometimes referred to as digital meters, which display changing peak sample values. These types of meters are used in digital mixers, effect processors and DAWs. Good practice dictates that when using these types of meters 3dB of headroom should be allowed to accommodate inter-sample peaks and avoid distortion. A peak level of -3dB is therefore required.


Neither True Peak Programme Meters or Sample Peak Programme Meters are useful for displaying perceived loudness. What is needed is a form of metering that can show peak levels and a history of loudness measurement over time.


Caption - VU meters

The VU meter was developed in 1939 to display signal level in audio equipment. Due to the ballistics of its meter, it is unable to show peak levels, or spikes in volume. It is therefore not good at showing peak levels. Interestingly, this limitation makes it better at showing average level, which is loudness, and this explains why it has remained popular. However the VU meter cannot tell us what a recordings average loudness is over it duration.


Caption - Measuring loudness

There have been serious challenges in developing a method for measuring loudness and perhaps the greatest is the variety of factors which effect its perception.


Caption - Factor 1 - Human variations in loudness perception

Firstly, we all perceive loudness differently. Whilst there isn't much we can do to address this, and it isn't the most important factor, it is important to acknowledge it.


Caption - Factor 2 - Environment

Secondly, loudness perception changes depending on the environment. For example, if the background noise is very loud, such as in a car or on a flight, we are more accepting of higher loudness ranges.


Caption - Factor 3 - Mood or tiredness of listener

Thirdly, loudness perception varies depending on the mood or tiredness of the listener.


Because of factors such as these, loudness metering methods must be predicated on average perception. Despite these limitations and many other complications, loudness metering is still a valid and useful way to arrive at good equitable and natural dynamic range and loudness and ensure that differences between commercials, music, film and video are minimised.


Loudness metering is increasingly being adopted by broadcasters and sound, mix and mastering engineers too.


Caption - Loudness metering

Loudness metering can be a confusing and complex subject so we are going to simplify it and give some practical advice.


The new standard for measuring both loudness and peak level is known as ITU BS.1770. ITU stands for International Telecommunication Union. BS.1770 is a specification that contains algorithms for loudness metering. This standard is used for a new generation of combined peak level and loudness meters such as this TC Electronic LM2 loudness radar plug-in.


To use a plug-in such as this simply insert it on the master output.


There are a few things to note ..

  1. Firstly, loudness metering ignores momentary peak level signals so its good practice to keep an eye on these and ensure that PPM peak level does not exceed -5dB.
  2. The basic unit for programme loudness measurement is LUFS (loudness unit full scale) and the target value should be -23.0 LUFS.
  3. It is useful to have loudness meters that display momentary loudness and loudness over time. This plug in provides a visual display of momentary loudness on the outer ring, and loudness over time on the radar display. Excessive loudness is shown in yellow, acceptable in green, and low level loudness in blue. The target loudness is at the intersection of the green and yellow rings.
  4. A single numerical programme loudness display will tell you the overall loudness level. When you finish metering you will want this to be close to -23 LUFS.
  5. Loudness range is measured in LU's, and shows the variation in loudness. It can be used to judge if compression should be applied. Loudness range becomes important if your recordings are being targeted at a specific platform. For example, for home cinema you will want a wide loudness range of around 20 LU in order to maintain dynamics. But for in-car listening you will want a narrow loudness range below 8 LU to ensure all of the recording is audible.
  6. Loudness metering only works with minimum durations so you should think about measuring loudness over the duration of a piece, or for no less than 20 seconds of average or loud parts of the programme material. The LM2 uses a loudness history display that advances during playback. Here the loudness radar history is set to 4 minutes.

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