Home Studio Practioner – Metering 101
A while ago a new term appeared: Loudness Units. The new standard of measuring audio levels in LUFS meant that we had to adopt and change our measuring tools. Here’s how.
by Luka Sraka, July 2017
This months Home Studio Practitioner topic was inspired by the Freebie of the Month article in this same issue in which I reviewed the Youlean Loudness Meter. We have always used some kind of audio level meters in audio production. From traditional VU meters that are still seen on traditional mixing desks and outboard gear, to RMS and peak meters that we know from our DAW. A while ago a new term appeared: Loudness Units. The new standard of measuring audio levels in LUFS meant that we had to adopt and change our measuring tools.
In short, the new standards that measure audio levels in loudness units or LUFS instead RMS were developed by the International Telecommunication Union (ITU) with the goal of providing a consistent way of measuring loudness and provide guidelines especially for broadcasting. These guidelines have now become law in the US and elsewhere.
The problem with the older measuring standard using RMS was that the perceived loudness of two audio signals that have the same RMS could be different. The new industry standards that are now adopted pretty much everywhere were developed basically to stop advertisements from being much louder in between the programs on radio or television. But let’s start with the old standards.
Before the age of digital audio production VU meters were used to meter audio signals. They can still be found on traditional mixing desks, outboard equipment or on your parent’s old radio. VU stands for Volume Unit and the proper name for a VU meter is SVI (Standard Volume Indicator). It was standardized in 1942 by the Acoustical Society of America for the use in telephone installation and broadcast. 0 VU is often referred to as 0 dB in the early days of digital audio.
A commonly used way of determining the level of audio has been to measure sample-peak level. Measuring peak level is somewhat misleading. Trying to be louder and louder forced producers and mix engineers to heavily compress, limit and maximize audio resulting in inconsistent audio in terms of loudness. True peak and RMS measuring were adopted later which was much better. RMS is short for Root Mean Square and to put it into simple terms it means the average signal. RMS measuring is very representative of the perceived loudness of audio signals and was and still is very popular.
The Loudness Units relative to Full Scale or LUFS was standardised in March 2011. The term Loudness, K-weighted, relative to Full Scale or LKFS term is also used. LUFS or LKFS metering is even better than RMS metering. The LUFS metering is a combination of Perceived loudness and the true peak level measuring. Hence we have a number of international broadcast standards. One unit of LUFS/LKFS is equal to 1 dB. The target levels are specified in various broadcast standards, but only vary slightly. For example, ATSC A/85 standard recommends a target of -24 and uses the LKFS term and the EBU R128 (one most commonly used for music production) standard sets the target level at -23 and uses the LUFS term. The differences are there because of different ways the standards work. The EBU R128 uses a gate that stops measuring when audio signal drops below a certain number. Because of this gate the measurement becomes much more cross-genre friendly allowing, for example, classical music to be as loud as pop music. If measured without gate, most measurements are equivalent to -24 LKFS/LUFS.
Audio deserves to be reproduced respectfully. With the new measuring and standards production, post-production and broadcast professionals now have a valuable and efficient set of tools in the so called loudness war.
Till next time!