Loudness
Compliance with audio loudness levels is a key component in delivering a sound mix. This is particularly important when mixing for broadcast delivery, as if you don’t meet the right specs, the broadcaster will fail the mix and send it back, possibly delaying the whole programme delivery or airing. I.e. Making you pretty unpopular.
Although not as important, loudness is also increasingly something to be aware of when mixing for online platforms such as YouTube or Instagram. I’ll consider how this differs in a follow up post.
Tough LUFS
The standardised measurement of loudness that is used in the UK and Europe is LUFS (pronounced L-U-F-S or ‘LUF(F)S’). This is an abbreviation of Loudness Units Full Scale. In the US, the same measurement scale is also used but is referred to as LKFS.
The purpose of this unit is to measure average loudness over an extended period of time, while taking human hearing and our perception of sound into account.
LUFS are measured via a specific type of metering plugin. I’ll go into detail on some of these in a follow up post.
Waves WLM Loudness Meter
-23... Is The Magic Number
The adopted standardised guide for loudness in Europe and the UK is EBU R128. The guide sets out that any broadcast delivery requires a loudness level of -23LUFS. This is an integrated / long-term loudness target which essentially means the average loudness over an entire programme. This is the opposite, if you like, of momentary loudness which measures the loudness of the last 300 milliseconds of a programme.
The idea behind using loudness as a measurement is to allow for a more dynamic mix. This means you could have some loud bits, you then might have some quieter bits. As long as the end LUFS reading is -23, you’ll be in a solid position with QC*. The aim is therefore to move away from the much documented ‘loudness wars’ of the 2000s which saw music and TV programmes becoming louder and louder via excessive compression and limiting in efforts to compete for viewers’ attention. This resulted in broadcasters receiving numerous complaints.
Wiggle Room
1 loudness unit in LUFS is measured as 1LU and represents 1dB change in loudness. The difference between -23LUFS and -22LUFS is therefore 1LU.
EBU R128 states that “a wider tolerance of ±0.5 LU is permitted”. This means that you can be within a +0.5 or -0.5dB range of the target loudness. Therefore, anything between -22.5 and -23.5 LUFS will be acceptable.
Other Considerations
- Maximum True Peak
There are three other important requirements to take into account. The most important is to ensure that no signal exceeds -1 dBTP (True Peak). This means that nothing throughout the programme should be louder than this. The BBC delivery specs recommend that no signal exceeds -3dBTP. It’s therefore sensible to set the output ceiling level of your limiter to -3 or -4dBTP in case the signal gets overloaded at any point and spills over. Some mixers set their limiter ceiling to -6dBTP just to be extra cautious.
- Short-Term Loudness
EBU R128 also refers to a “Maximum short-term loudness” of -18LUFS. Short-term in this context refers to the previous 3 seconds. This is something you can keep an eye on with your meter as well.
- Loudness Range
There is also a ‘loudness range’ that is sometimes referred to as ‘LRA’. Again, the BBC specs state that an LRA of no more than 18LU is recommended, with dialogue on factual programmes not exceeding 6LU.
Final Thoughts
To summarise, don’t get too thrown by mentions of dBs and LUFS as the underlying concepts and targets are actually quite straight forward. Just focus on getting a well-balanced mix, trust your ears, and make sure you hit an integrated level of -23 LUFS that doesn’t exceed -3dBTP and you’ll be grand.
Also, remember to always check the actual broadcaster’s delivery specs as these can change over time or differ slightly to the norm.
Happy mixing!
*QC is the abbreviation of ‘Quality Control’. A generic term used to describe the broadcast delivery partner who will check / test the full delivery package (including picture) to ensure it’s compliance with all the required specs.
Comments