Especially if you work in the broadcasting industry, you may be familiar with standards such as EBU R128. It was created to ensure a similar perceived loudness level for the entire programme without sacrificing dynamics. If you only looked at the peaks of your audio signal, you would never be able to tell how ‘loud’ it actually is. Commercials, which are highly compressed and limited, may have the same maximum peak level as someone reading the news, but the perceived loudness is completely different. This is why broadcasters use different measurement methods such as R128 to solve this problem.

GLM offers you a standard Loudness SPL calibration. You can first select the standard you want to use:

For EBU R128 a Standard Loudness Level (LUFS) of -23 dB is recommended and chosen.

You can then select what SPL this LUFS level of -23 should result in at your listening position.

The moment you click on ‘Start calibration’, a high-pass filtered pink noise is played from a loudspeaker and GLM finds out how high the level of this noise must be to achieve the SPL value at standard level, for example 73 dB.

This is what this signal looks like on an analyser:

Very important: This noise does NOT come from your source. It is generated by the build-in signal generator of your speaker. So if your source is not a full level digital source, the actual levels coming from the interface may be different. The only way to deal with these different levels is to adjust the level manually. Play your test signal (should also be bandpass filtered noise), place the microphone at your listening position and check the SPL value displayed. Then adjust the GLM's sensitivity control (volume fader) and create a level preset.

For those using a digital source, you can rely on the measured values.

If you click on ‘Confirm’, you will return to the main window. dBSPL is now displayed above the fader. You can switch back by clicking the "SPL" button below "Dim All".

If you now listen to program that is mixed to -23 LUFS, you will get an SPL of approx. 73 dB. As said: if your playback chain does not change any levels. The best way to test this is to create a noise in the DAW (or even a sine tone, set to 500 Hz for example, 1 kHz is really no fun ... ;-)), change the level so that it shows -23 LUFS in your R128 metering device or plugin, and set the level fader in GLM to the preset value, which was set to 73 dBSPL. The microphone reading will then be 73 dBSPL.

A common misunderstanding: setting the GLM fader to 73 dBSPL will NOT ensure that your music or sounds will play with 73 dBSPL. 73dBSPL is achieved when we are at -23 LUFS. Streaming services such as Tidal play at around -14 LUFS when loudness normalisation is activated, for example.

Generally speaking, you only need this function if you are working with these standards. If you are interested in at what level you're monitoring, you can check the measured values of the GLM microphone or use the advanced functions of the 9320A.