TOO LOUD!

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TOO LOUD! BACKGROUND Many people have been in the position of telling a family member, friend or neighbour to turn it down.

Loudness can be used as a way of grabbing a person’s attention, since we are all familiar with raising our voices or shouting in order to be heard. However, excessive sound levels can be a nuisance and especially if prolonged.

In a similar manner to the previous example where we raise our voices to be heard this can be extended to the music industry. For a long time there has been the so called loudness wars where audio was mastered so that it would sound louder as it would help the music stand out from the rest, the history of which could be traced back to the 50’s where the bar owner would set the overall jukebox level and as a consequence the louder record cuts would be more popular.

Now as music consumption shifts to streaming services these mediums are now looking to improve the continuity and preservation of sound quality by introducing more sophisticated normalizing methods in a bid to preserve the dynamic range.

In broadcast, loudness has been used in adverts, much like the previous example, to grab your attention even when you are not in the same room as the TV, which as a result causes big loudness differences between programmes. This has been a common complaint from consumers which has been levelled at a number of broadcasters prompting them to take action.

There are a large amount of programmes and media being created for TV by a number of differing studios and different content producers, therefore it is essential that standards are adhered to in order to maintain continuity between programmes and adverts to avoid large sound level jumps.

Previously loudness in broadcast has been measured using what was known as PPM meters (peak programme meters) although this method of metering did not accurately reflect the way humans perceive loudness.

HUMAN HEARING MECHANISM Measurement and perception of loudness is not as simple as it would first seem. Firstly, the human hearing system does not perceive all frequencies with equal loudness, since the shape of head, ear and ear canal has an effect on the perception of sounds and as a result humans are more sensitive to sounds in the 2 kHz-4 kHz range and the frequency dependence is not consistent but changes with frequency (http://www.sengpielaudio.com/ Acoustics226-2003.pdf). In addition when considering loudness in surround sound systems the HRTF (head related transfer function) has an even greater effect and curiously sounds which come from the rear are perceived as louder.

Loudness perception is also influenced by the duration of the sound, since studies have shown that sounds with as short a duration as 200 milliseconds will sound just as loud as a constant sound at the same level. In addition, loudness perception is related to the SPL or (sound pressure level) and the hearing system averages SPL over a 600-1000 millisecond period, varying the duration of the sound in intervals from say 100, 200, 300 milliseconds the sound will be perceived as louder up to 1 second after which the perception of the level will be constant again.

Measurement of musical signals or sounds which are highly dynamic in nature is problematic when trying to obtain an accurate SPL measurement. Therefore an averaging method

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canford.co.uk (Leq), which measures the sound level over a specified period of time coupled with what is termed an A weighting factor is employed. The A weighting places more emphasis on the mid to high frequencies in a bid to approximate human hearing, with the complete measurement term being called LAeq, the ‘A’ signifying an ‘A’ weighting filter is included in the measurement.

True Peak

NEW LOUDNESS MEASUREMENT

Loudness Range

It can be seen that human perception of loudness is complex therefore in order to find a loudness measurement method which best matches’ human hearing a number of institutions and manufacturers, like ITU (International Telecommunications Union), EBU (European Broadcast Union) incorporating manufacturers like TC Electronic have carried out several years of research to find a better method. As a result this has culminated in the EBU R128 loudness standard called LUFS or LKFS measure, (loudness units relative to full scale). And a new loudness levelling target of -23.0 LUFS, where 1 LU (loudness unit) is equal to 1dB relative to the ungated LUFS measure.

However, this is not the only implementation there are also a number of additional technologies which have been included and these follow.

The loudness range or LRA describes the overall program level range from the quietest to loudest part and is specified as an LU. This also helps in avoiding extreme levels since the top 5% and lowest 10% is excluded in the measurement, therefore loud explosions or long silences would result in a wide ranging loudness. The LRA value helps provide guidance on the need or not for compression.

K-Weighting

TC Electronic who were also part of the loudness research and who published several papers on the subject, which can be found at http://www.tcelectronic.com/loudness/literatureglossary/ have implemented the technology in their loudness processors, which include the DB6, DB2 and Loudness Pilot, these are aimed at the professional broadcast, however there is also the Clarity M which is aimed at the professional and home user wanting a more scaled down version.

A ‘K’ weighting curve has been developed to provide a better match between the subjective perception of loudness and the objective measurement. The ‘K’ weighting consists of a pre filter which accounts for the shape of the head and a weighting to take account of angle of arrival, particularly relevant for surround sound systems where it was previously mentioned that sounds from the rear are perceived as louder.

In addition an RLB filter (revised low frequency B weighting) is also included, this takes into account the fact that humans are less sensitive to lower frequencies. In simple terms the ‘K’ weighting filter is similar to that of the previously mentioned (A) weighting filter where less emphasis is placed on the lower frequencies and a slight shelving filter is used at the higher frequencies, essentially enhancing the higher frequencies.

Gating Measuring average levels of program material may not be ideal since films or TV programs may include long passages of low level background sounds which would affect the overall level reading. Therefore a gate is used which pauses the measurement when the level drops below a threshold of -10 loudness units relative to the ungated audio material. This also helps in creative advertisement where short silences are used to get round breaching maximum levels.

True peak Is a measurement that looks at inter sample values in order to identify over shoots that may happen further down the processing chain for example in digital to analog conversion when samples are interpolated. True peak uses the unit’s dBTP (Decibels True Peak) which is referenced to the digital full scale value 0dBFS

NOT SO LOUD Audio broadcast level loudness now follows the new EBU R128 standard utilising the previously mentioned LUFS levelling standard with a target loudness of -23LUFS. This change in loudness standard was needed in order to help curtail the level jumps between programmes and adverts.

Content media consumption now extends to streaming services like Spotify, Tidal, ITunes and You Tube, these services also utilise the EBU R128 standard to normalise their content, however these use a slightly higher level than that of the TV broadcast standard, normalising between -12 to -16 LUFS. It would seem that the new loudness protocol has helped put the dynamics back into TV and music and help create a level playing field overall.

87-0112 TC ELECTRONIC DB6 MULTI 1 AUDIO PROCESSOR

87-0121 TC ELECTRONIC LOUDNESS PILOT

UK sales tel: +44 (0)191 4181122 email: sales@canford.co.uk | Int sales tel: +44 (0)191 4181133 email: international@canford.co.uk