Loudness meter: what it is and how to read one.

What is a loudness meter?

A loudness meter is a tool that measures how loud audio sounds to a person. It filters the signal to roughly match human hearing, averages its power over time and shows the result in LUFS. Two songs that read the same on a loudness meter should sound about equally loud, even if their peak levels are far apart.

That matters because streaming services turn every track to a set level, and broadcasters require one, and both base it on this measurement. A loudness meter tells you where your audio stands before it gets there. You'll also see it called a LUFS meter or an LKFS meter. It's the same tool: LUFS is the unit, and LKFS is its name in US broadcast documents.

What a loudness meter shows

Most loudness meters show the same set of readings. Each one answers a different question:

Momentary and short-term move as the audio plays, so most meters also keep their highest values, shown as momentary max and short-term max. Some add PLR and PSR, which compare loudness with true peak to show how hard a master is limited. For more on two of these readings, see what LRA means and true peak vs sample peak.

How a loudness meter works

Meters that follow ITU-R BS.1770 all take the same steps. A filter called K-weighting lifts the highs by about 4 dB and rolls off the deep lows, roughly the way the ear hears. The meter then measures the power of the filtered signal in overlapping 400 ms blocks.

For the integrated reading, it also applies two gates. Blocks below −70 LUFS are ignored, then blocks more than 10 LU below the average of what's left. That's why a quiet intro barely changes a song's number. The full method is in how LUFS is measured.

Because the method is fixed, two meters that follow the standard should agree on the same whole file. When they don't, the cause is almost always a setup difference, covered in why two loudness meters show different LUFS.

How to use a loudness meter

1. 01Measure the final signal. Put a plug-in last on the master bus, after the limiter, so it reads what you are going to export. For a finished file, use a file analyzer.
2. 02Reset the meter. Integrated loudness adds up from the moment the meter starts. Clear it before you press play.
3. 03Play the whole track. Looping the chorus or skipping the intro gives you the loudness of that part, not of the song.
4. 04Read integrated at the end. It settles as the track plays. The momentary value at the point you stop means very little.
5. 05Check true peak. Look at the highest value for the whole track. Above −1 dBTP, a peak can clip when a streaming service encodes the file.
6. 06Compare with a reference. Measure a released track you like in the same way, so the number means something for your style.

Turning up your monitors or headphones doesn't change any of these readings, because the meter reads the signal, not your speakers.

What's a good loudness reading?

Normal audio reads negative, and closer to zero is louder: −8 LUFS is a loud master, −23 LUFS is European broadcast level. There's no single right number, because it depends on where the audio goes:

For music, the streaming numbers are playback levels, not delivery rules. A louder master is turned down, and the loudness penalty calculator shows by how much. For broadcast, the number is a requirement. See how loud to master for the levels professional engineers deliver, and the loudness targets table for every platform.

Loudness meter vs peak, RMS and VU meters

So a loudness meter doesn't replace peak metering. A master can sit at a sensible LUFS and still clip, which is why most loudness meters show true peak beside it. Use both: LUFS for how loud, true peak for how safe.

Loudness meter vs decibel meter

Search for a loudness meter and you'll also find decibel meters, sound level meters, SPL apps and classroom noise meters. Those listen through a microphone and report dB SPL, the sound level in the room. A loudness meter reads the audio signal itself and reports LUFS.

They answer different questions. A decibel meter tells you how loud a room is. A loudness meter tells you how loud a track is, at whatever volume it gets played. A microphone reading can't predict a file's LUFS, because playback gain, the room and the microphone all change it.

Kinds of loudness meters, including free ones

• Built into your software. Logic Pro, Nuendo, Premiere Pro and DaVinci Resolve all include a loudness meter, so check your metering menu before you download anything.
• Plug-ins. They sit at the end of the master bus and show loudness while you mix. Free versions exist, and paid ones add history graphs and reports. A plug-in only sees the audio in that session.
• Online meters. Drop in a file and get the readings, with nothing to install. They're mostly free, but they measure files only, with no live metering.
• Apps. LOUDMETER: Menu Bar meters your DAW or anything else your Mac plays, without a plug-in. The free iPhone and iPad app analyzes files or mirrors the Mac's live meters.
• Hardware. Standalone units found in broadcast studios. They're reliable but expensive, and more than most home studios need.

Choosing a loudness meter compares these kinds in detail, and the best free online LUFS meters shows how 11 online meters did in our tests.

Try a free loudness meter now

Drop a WAV, MP3, AIFF, FLAC or M4A into the free online loudness meter. It shows integrated, short-term and momentary LUFS, true peak, LRA, PSR and PLR in your browser, marks true peak overs on the waveform and plays the file at each streaming service's level. The file is never uploaded.

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