Metering your audio signal may be the most important part of tracking, mixing and mastering. Let’s unravel some of the mysteries of audio metering so you can work with precision, knowing which meter to use and when.
What’s the most important part of your recording chain? Is it the microphone, or mic preamp? Your choice of DAW? How about your speakers, or the amplifier driving them?
The correct answer is: none of the above. In fact, it’s the humble meter.
Surprised? Well, consider this: Without accurate level measurements, you wouldn’t know how to set input trims, which could result in noise (or, worse yet, distortion) in your signal. You wouldn’t know when your system was at the onset of clipping. You wouldn’t know how effective your gain reduction plugins are on the signals they’re trying to rein in. And you wouldn’t be able to deliver a properly constructed mix for mastering.
In this article, we’ll unravel the mysteries of audio metering and discuss how best to use it.
Back in the days of analog recording, meters actually displayed electrical level as a representation of audio level. There were three basic types of meters commonly used:
This video overview shows some of the configurations and features included in the Dorrough:
Fall in love with LUFS
Today’s digital technology enables alternative types of metering that can be used in combination with (or instead of) traditional meters. For example, unlike the human ear, which has different sensitivities to sound at varying frequencies (i.e., we perceive volume changes in mid-range frequencies much more acutely than at low and high frequencies), old-school level meters can’t distinguish between frequency ranges. To account for this, an entirely new metering scale, called LUFS (an abbreviation for “Loudness Units Full Scale”) has been created to account for how we actually perceive loudness, not just average levels or peaks. (There’s a further refinement called LKFS, which uses something called weighting to account for differences in frequency response; however, for all practical purposes the two terms can be used interchangeably.)
It’s important to recognize that there’s a significant difference between the units of measurement used by VU or PPM meters (dBVU and dBFS, respectively—the “FS” stands for “Full Scale”) and those used by loudness meters (LUFS). In addition, loudness meters such as the Waves WLM Plus Loudness Meter plugin provide actual numerical readouts instead of an abstract needle swinging or segments lighting: either you hit the target or you don’t, no interpretation needed.
The LUFS scale is used extensively in the broadcast television industry, where government standards mandate consistent volumes between channels as well as when a channel goes from program material to commercials. It’s also used in video games and online delivery systems. Some game companies specify that the mix for a music track has to fall within a defined LUFS levels so they can better predict how it will balance with the other game sounds.
Know your timescales
Another important concept in modern loudness metering is the timescale of the measurement. The laws of psychoacoustics state that we perceive loudness from the average, rather than the momentary peaks in a sound – in other words, a very short transient burst (even at a high level) won’t affect our perception of loudness very much, but a similar one lasting half a second or more will have great impact, to the point where it can actually cause discomfort.
Several timescales have been established and standardized over the past few years, the most common of which are:
The Waves WLM Plus Loudness Meter plugin displays all four of these timescales simultaneously, as well the overall loudness range. It also offers a number of advanced features, including an integrated True Peak Limiter and Gain and Trim controls for loudness normalization and correction, with readouts for most common weighting types. In addition, it issues warnings when loudness targets are not met or are exceeded and registers when Overs or Unders (individual samples that cause digital clipping) occur.
Here, you can see your way around the many features of the WLM Plus Loudness Meter plugin:
The best approach is to find the meter type (or combination of meter types) that works best for your application and the music you’re recording, mixing or mastering. For example, if you’re mostly just recording demos in a home studio, a simple but correctly calibrated VU Meter may be all you need to avoid overload and ensure that you are leaving yourself sufficient headroom. If you need more precision – for example, if you’re doing mastering or working on commercial releases – the Dorrough plugin is a good choice. For the ultimate in clip avoidance and accurate measurement of overall loudness, the WLM provides all the metering tools you’ll ever need, in even the most demanding mixing, mastering and broadcast sessions.
Bear in mind that there’s no reason to limit yourself to just one meter type. Give yourself the best of several worlds! After all, it’s quite possible for a signal to look one way on one type of meter but quite different on another. Transient percussive sounds like tambourine, for example, usually cause only marginal movements on a slow-reacting VU meter, while a solo voice can sound relatively quiet even if a PPM meter is jumping around.
Once you’ve identified the meter type(s) you want to use, insert them not only at the end of your signal chain but wherever you feel you’ll need them (for example, it can be helpful to have meters both before and after dynamics processor plugins such as compressors or limiters).
And most importantly, check your meters frequently as you record, mix, and master. That’s the key to maintaining correct gain staging and avoiding nasty audio surprises.
For maintaining proper levels during mastering, see our essential tips for mastering levels.