In the audio industry all different disciplines have various industry standards. These standards must be abided by. Examples of disciplines that use stick to a specific standard to be determined of quality or required standard are Mastering for CD’s, DVD’s, Vinyl and Broadcasting. In this blog post I will be focusing on the Industry standards for Broadcasting.
When we get down to it, the most crucial problem for audio in broadcasting is the loudness of the broadcast. All over the world people have to constantly adjust their TV’s volume due to loudness inconsistencies in the channel they are watching. This is most commonly found in TV advertisements as each competitor wants to ‘appear’ louder than the next, they do this by using ‘excessive amounts of compression, limiting and maximization’ (tcelectronic.com, 2015) which leads to lo-fi audio production, which no listener wants.
I say ‘appear’ louder, above, as the loudness of audio is most commonly measured by its sample-peak level (measured amplitude on sample peaks, rather than the peak of the waveform, which may be up to 3 dB higher in amplitude[Youtube, 2015, Wikipedia, 2015]). But surely if the audio is being produced for an audience (ofcourse?!), and the loudness has to be governed by specific standards, it should be measured by perceived loudness? Well with a combination of measurements of perceived loudness and a more accurate measurement of audio called True-peak, many industry standards have been developed to suit the listener a lot better; thanks to extensive research and listening tests by independent organisations such as the Communications Research Centre (CRC) and McGill University, in Canada (tcelectronics.com, 2015).
When determining the standards the most important factors are:
- K-Weighting- Although two seperate pieces of audio may have the same Sample-Peak level, extensive research shows that they may well be perceived to have a different loudness. The basic explanation of K-Weighting is that it is a filter curve applied to audio channels.
The respective loudnesses from different channels are then summed and converted to a logarithmic scale (like dB) to give a loudness figure. (Nair, 2015)
- LKFS, LUFS & LU- When measuring sound LKFS, LUFS and LU are integral. LKFS and LUFS are abbreviations for, Loudness K-weighted Full Scale and Loudness Units Full Scale. These terms are used by the Internation Telecommunication Union (ITU) and the European Broadcasting Union (EBU) respectively and they mean the exact same thing. 1 unit of LKFS or LUFS is equal to 1 dB. When measuring broadcasting level, the LKFS or LUFS could be eg. -23 or -24 dB.
However, in order to aim for a more ‘traditional number’, a relative measure has been defined: Loudness Units (LU). Now, the broadcaster can set the target level (regardless of whether it is -23 or -24) to 0 LU, and again, one LU is equal to one dB. (Tcelectronics.com, 2015)
- Loudness Range, Program Loudness & Descriptors- The loudness range or LRA is the range of the loudness of audio from the absolute loudness point to the quietest, although this range does not include the top 10% and lowest 5% of the LRA to stop ‘extreme events’ from affecting the range. The LRA is quantified in LU. The program loudness is used to describe the average program level, it is quantified in LKFS or LUFS.
- Gating- When measuring Program Loudness, calculating the average level may not be as accurate as possible to be relevant to our perceived loudness so thats where gating comes in. A gate is placed at a threshold of -10 LU which pauses the calculation of the program loudness when the level goes under that.
- Target levels- ‘Target levels are specified in various broadcast standards, but only vary slightly. (Tcelectronics.com, 2015)’
- True-peak- ‘Since loudness measuring is based on an algorithm that builds on a study of subjective perception, in theory, program material that complies with the determined LRA and Program Loudness of a certain broadcast standard can in fact overload if normalized the traditional way (quasi-peak or sample-peak). Therefore, normalization is also part of many broadcast standards, and to comply, broadcasters must use a true-peak meter.’ (Tcelectronics.com, 2015)
There are various broadcasting standards all over the world, I will be giving a brief overview of a few of the main broadcasting standards.
International Telecommunications Union (ITU)
The ITU is one of the most important broadcasting standards across the world as most other standards are based off of it.
‘The ITU standard concerns Broadcast Loudness and True-peak Level measurement, and the loudness part is based on an Leq measurement employing K-weighting, which is a specific frequency weighting…’ (Tcelectronic.com, 2015)
The most recent, updated, recommendation is the ITU BS.1770-3, published August 2012.
‘The P/LOUD group, which is part of The European Broadcasting Union (EBU), has defined the R128 standard based on ITU BS.1770. However, the group also added new tools such as a relative gate that ensures even more consistent loudness across genres and types of program material. Some of these tools have been implemented in the updated version of ITU’s recommendation: ITU BS.1770-3.
Basically, the R128 standard builds on 4 tech documents: EBU Tech 3341, EBU Tech 3342, EBU Tech 3343 and EBU Tech 3344.’
The ATSC A/85 was specified by the Advanced Televisions Systems Committee, this applies to US digital TV broadcasting.
It specifies anchor based normalization for regular programs, but all-source loudness normalization for commercials.
It also prescribes the ITU BS.1770-3 for all broadcasting.
‘TR-B32 is a Japanese broadcast standard that builds on ITU BS.1770-2, which means that a relative gate is employed. However, the target level is -24 LUFS/LKFS as opposed to the -23 LUFS target level of the EBU R128 standard which also employs the gate. As a rule of thumb, a gated measurement of -23 LUFS/LKFS equals an un-gated measurement of -24 LUFS/LKFS.’ (Tcelectronics.com, 2015)
‘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.’ (Tcelectronics.com, 2015)
LO’s Addressed: 10 ad 16
Nair, V. (2015). Loudness and Metering (Part 2) | Designing Sound. Designingsound.org. Retrieved 2 December 2015, from http://designingsound.org/2013/02/loudness-and-metering-part-2/
Tcelectronic.com,. (2015). Broadcast Standards | TC Electronic. Retrieved 2 December 2015, from http://www.tcelectronic.com/loudness/broadcast-standards/
Tcelectronic.com,. (2015). Loudness Explained | TC Electronic. Retrieved 2 December 2015, from http://www.tcelectronic.com/loudness/loudness-explained/
Wikipedia,. (2015). Peak programme meter. Retrieved 2 December 2015, from https://en.wikipedia.org/wiki/Peak_programme_meter
YouTube,. (2015). Final Cut Demo – true-peak vs peak sample metering for professional audio. Retrieved 2 December 2015, from https://www.youtube.com/watch?v=lQTxSyK-ATI