Audio metering: Everything you need to know

No matter if you’re working on an analog console or in a DAW, dialing in outboard gear, or putting the mastering touches on a mix, metering is an intrinsic part of everyday audio life. In this audio metering tutorial, we will touch on some common definitions, the types of metering available to you, and some of the tools to help you craft your best work.

Audio Metering 101

All audio meters are used to gauge some type of level. If you’re tracking, this could be the input level into the preamp, and likewise the recorded level into whatever you’re recording medium is. Meters react in a ballistic fashion, which is audio geek-speak for how the meter responds to the signal that is being fed into it. Think of it like the attack and release times on a compressor.

But not all meters are created equally, and there are situation-specific ones you’d want to have at your disposal depending on what you’re trying to accomplish. But first, let’s clear the air a little bit.

RMS vs. dBFS

Along with LUFS, these two make up the holy trinity of audio metering. There is often some ambiguity around these terms, especially for those just starting their adventures in audio. A very basic definition would be that RMS is the average loudness of a signal, RMS is the differential between the loudest and quietest portions of the audio being measured.  dBFS is a peak measurement based on electrical level. The maximum peak allowed before clipping in digital audio is 0dBFS. The dBFS unit is entirely a measurement of electrical level. There is no consideration for “loudness”.

Types of Meters

VU Meters

By far the most recognizable, the VU (volume unit) simply measures voltage.  They became a standard in 1942. They were inexpensive to manufacture and easy to integrate into professional and consumer gear alike. One of the reasons they caught on so quickly is that metering is primarily used to monitor input and output levels. Since VU meters present the average it helps with gain staging and finding the optimal signal-noise ratio. Depending on certain factors, VU meters also can provide inconsistent comparisons between wet and dry signals.

They are still used on certain types of gear, but when digital audio started to make its way to the forefront LED meters started becoming more widespread. Nostalgia for the golden days of analog recording has even inspired some companies to create plugins (like those from Presonus and Waves Audio) that translate digital metering into a VU meter simply for the aesthetics! VU plugins also have the advantage of being able to choose between multiple metering types while maintaining a vintage aesthetic.

Peak Meters

Even though peak meters were being developed during the Great Depression (yeah!) they are still one of the more advanced types you’ll find. Rapid transients are the most common reasons a signal clips. VU meters are really weak in this area, so peak meters became a fantastic supplement to them. Displays the peak of the waveform and holds it. They have an almost lightning fast attack time and are designed to ignore the fastest of transients. Attack is 10ms with a slow release so you can capture what it’s presenting.

Obviously this makes them one dimensional, but somewhat exceptional. This allows engineers to push level while not necessarily worrying about the highest peaks. Conversely, they have a slow release which allows for more time to monitor peaks. The downside being they don’t really tell anything about perceived loudness, so this type of meter is mostly used in gain staging to protect the gear.Peak meters are especially useful on fast transient sources like drums, percussion, and vocals.

Dorrough Meters

Dorrough is the kind of loudness meter most of us are now familiar with, as they are commonplace in the DAW world. They provide a reference for both peak and average, which is necessary in modern recording. They run on separate ballistics to provide the best display of peak and average. There are multiple companies that offer great paid alternatives to this type of metering, like the one from Waves.

Loudness Meter

One of the newer types of meters measures in LUFS, which is a global standard for determining loudness. This model delivers three readouts – short term, momentary, and integrated. Short term is fantastic for metering dialogue. Integrated gives you the overall loudness measurement which is great for program material. And short-term is useful for mixes and masters of music audio and provides useful reference when comparing your track against a reference mix.

LUFS meters also provide representation of loudness range, which is the differential between the loudest and softest points in the audio. This helps engineers determine what the real dynamic range of the entire thing. The digital world offers more headroom than analog, but when you go over the threshold things become very different. In the analog world, this can provide some very pleasant side effects like compression and saturation. But in the digital world if you break that threshold things become very nasty very quickly. Digital clipping is something that should be avoided at all costs.

K Metering

The K system is a fascinating audio metering concept developed by renowned mastering engineer Bob Katz. It began as a journey to create a standard for loudness measurement for audio across the world. It encourages consistency in monitoring and recording levels while discouraging extreme loudness. Average and peak are combined. It can be a bit cumbersome to setup, as there are multiple things that need to be addressed – like monitor calibration.

With the K system when the meters read 0 there should be a consistent level of loudness. These are dependent on which type of K metering measurement you’re using. Monitoring levels should be around 80-85dB, which is the ideal volume for monitoring. It’s not loud enough to cause fatigue, but it accommodates for the Fletcher-Munson curve. The three main types of scales include K-12, K-14, and K-20. The number is the amount of headroom over 0 on your RMS meter (12, 14, and 20) and alludes to the dBFS level that should be considered “0”.

These options are meant for different mediums as well as the dynamic range. K-14 is probably the most familiar to you as it is the preferred type for modern music production. K-12 is used in broadcast and K-20 for large ensembles like orchestras. A lot of limiter plugins like the FabFilter Pro-L even have presets for the different variations.

Audio Metering Tools

Spectrum Analyzers

Overview of frequency content is just as important as level. This type of meter breaks things out by band and amplitude. These show a graph of the 20Hz-20kHz (and sometimes extensions in range up or down) frequency spectrum and where the overall sonic balance is in whatever audio content is being sent to it. It starts with the low end on the left and progresses into the high range. Vertically represented is the amplitude of the frequency spectrum. There can be positive or negative values.

This type of meter helps to ensure our mixes are balanced, but that doesn’t mean the readout should look flat by any stretch. There is a very delicate frequency balance required to makeup the sonics of a great mix. It’s a moving target, meaning it’s different from genre to genre, song to song, even section to section!

Spectrum analyzers provide a great visualization of the overall sonic picture. But always remember – it’s about the ears and not the eyes.

Phase Correlation Meters

Physics play a big part in what we do as audio engineers. With considerations like phase alignment and polarity, phase correlation meters can help determine how healthy the phase relationship is in the elements of a mix. Put simply, these meters measure the phase relationship between the left and right channels of a stereo source. A little bit of phase is a good thing though. If the left and right signals of a stereo mix were to be in perfect alignment it would just be mono!

Checking your mix in mono is a great way to help define balance between all of the different elements, especially sources captured with multiple microphones like drums and guitars.

Vectorscope

More common in film and broadcast audio than in music is the vectorscope. This tool is used to analyze the difference between the left and right channels of a stereo source and is another way to be aware of any phase issues.