A True Measurement of “Quality” Loudness in Audio Mastering

You love the loudness and quality in mastering. After all it sounds good anywhere. But if you have participated in the loudness wars, that destroys the dynamics, ambiance and clarity of recordings. Before, albums are pleasing and exciting to listen; they have that “quality” loudness. Today, you will only find it tiring to listen because of tracks is loud and all sections of the song are loud. This post will highlight a probable approach that could end the loudness wars.

Measure loudness quality not in terms of RMS average

Mastering engineers often measure the loudness of each track in mastering in terms of RMS average. They do this because average RMS measurement is closely correlated to actual loudness perception of the human ear. This is measured in dB for example see the screenshot below taken from Adobe Audition waveform statistics:

For example in the above screenshot, the track has an average loudness of -26.25dB (left channel) and -26.34dB (right channel). There are two channels since all tracks for mastering are in stereo. This is how the waveform would look like:

As you can see there is still a lot of headroom in the waveform because this is not yet mastered and the dynamics are well preserved. With proper mastering techniques, the sound could further be improved and make it sound as big as possible without losing the original dynamics.

After mastering; it averages above -12dB for all tracks in the album. This is very common for modern album releases particularly alternative rock, hip hop and pop music. Above -12dB is considered to be very loud subjectively and almost all dynamics in the recordings are gone. For example the song “Broken, Beat & Scarred” by Metallica in their album “Death Magnetic” averages around -7.01dB (left channel) and -8.2dB (right channel) and this is how the waveform looks like:

As you have observed, there is almost no headroom left and if you listen to this repetitively; your ears will get tired very easily. This is because the dynamics of the recordings are lost and all that is left are loudness.

Sadly a lot depends on brick wall limiter to increase the loudness (average RMS) of the track to as high as possible; compromising the dynamics and quality of the mix down. Therefore it is not reliable to depend only on the average RMS to assess the loudness quality of your mastering results. A better measurement for mastering quality is important.

True Measurement- A Balance of Loudness and Dynamics

The recommended and reliable measurement of quality loudness in mastering is to consider dynamics. Dynamics is the difference between the minimum and maximum RMS power (check if the mastering software provide these statistics). For example if the minimum RMS power is -65.75dB and the maximum RMS power is -10.75dB then the dynamics of the audio track can be approximated -65.75dB – (-10.75dB) = -55dB. Higher figure indicates a nice presence of soft and loud sections (such as a soft stanza and a loud chorus) of the mastered track. Unfortunately, as you increase the loudness you decrease the dynamics of the audio material. See the figure below:

For example if you want to make your recordings very loud by targeting around -10dB loudness then the dynamics would suffer because it would become squashed due to compression/limiting. Also if you want to have that nice big dynamics, then your master recordings run the risk of not being competitively loud.
Therefore to achieve that quality loudness is to settle the balance between objective loudness and dynamics. How are you going to achieve this?

How to achieve balance of loudness and dynamics

First, it requires good mastering techniques and great set of ears to achieve a balance between loudness and dynamics. Below are the recommended tips:

a.) Listen to the song first before mastering. Listen to it very closely and pay attention to the important sections where dynamics of the song are emphasized.

b.) When applying compression and limiting, listen again to make sure the dynamics are still preserved and not squashed.

c.) To avoid increasing the dB RMS level using limiter that could also squashed the dynamics, try focusing on the multi-band compression techniques first or EQ to add presence to the track. Multi-band compression allows you to increase the loudness on the critical band 300Hz to 3000Hz (all other frequency bands untouched) where ears are very sensitive to loudness. Also you can add a boost at this frequency range (e.g. 2000Hz Q=0.5 +2dB) to improve the presence and subjective loudness of the track.

In this technique, your track “appears” loud and big to the ears while the average RMS is not too loud. You preserved the dynamics in this case.

c.) Listen to your favorite loud recordings before the loudness war and imitate their loudness and dynamics. You can do this by measuring their average RMS level and dynamics using your mastering software and then targeting your work to achieve this level using different mastering techniques.

Content last updated on June 20, 2012