-as of [2 NOVEMBER 2024]-

*UNITS* –>

*LUFS*
(“Loudness Units Full Scale”)

(aka ‘LKFS’)
(“Loudness K-weighted Full Scale”)

K-Weighting

A form of electrical filter which is designed to mimic the relative sensitivity of the human ear to different frequencies in terms of pereceived loudness.

It is broadly similar to the A-Weighting curve, except that it adds a shelf boost above 2kHz.

This filter is an integral element of the ITU‑R BS.1770 loudness measurement protocol

*RMS*
(“root mean square”)

*TRUE PEAK MAXIMUM*
(spotify standard is -1 db)

*PEAK / TRUE PEAK / LUFS / RMS*
(“piano for producers” link)

We all want our tracks to sound loud

But have you ever stopped to ask yourself:

how loud is my song?

It’s a simple question,

but I would need more info before I can answer.

Why?

Because “loudness” can refer to a variety of different things, depending on the context

It could theoretically mean any of the following:

How loud the song is at max volume

The average loudness of the whole song

The average loudness of a section of the song

The perceived loudness of a song

This is why there are so many different ways to measure levels: each is designed to measure a specific characteristic of the signal.

Peak, True Peak, RMS, LUFS –

I’m sure you’ve all heard these terms thrown around.

While they all measure gain, each does so in a different way.

Therefore, it’s imperative to learn what the different measures of loudness are and how to use that information to better our mix

Let’s jump in...

Point in Time vs. Integrated (Average) Reading

There are 2 main types of ‘loudness measurement’ –>

Point in Time:

measure the ‘signal level’ and a specific ‘point’ in ‘time’

(how loud is the song RIGHT NOW?)

Integrated: measure

the AVERAGE signal level over a given time period –

how loud is the song in general?

‘Peak’ and ‘true peak’ are ‘points’ in ‘time’

They measure the signal level at a specific point in time

LUFS and RMS are integrated

They measure the AVERAGE signal level over a period of time

This is the most important thing to understand:

Peak and True Peak:

tell you the volume at a specific point in time

LUFS and RMS:

tell you the average loudness over a specified time

Peak and True Peak:

Point-in-Time Loudness Measurements

Peak

the maximum level that a signal reaches –

the “loudest” point in your signal

To be honest, we don’t really care that much about peak in today’s world of floating point DAWs.

The only thing we need to be aware of is that the PEAK level on our master should not eclipse 0.0 dB

It’s fine if you are in the red (peak of over 0.0 dB) on individual tracks

but make sure that your master Peak stays at or below 0.0.

“True Peak”

the maximum level that a signal reaches –

the “loudest” point in your signal.

True Peak is just a more accurate version of peak.

It essentially measures peak but at a more detailed level.

I can get more into the technical difference, but it really doesn’t matter.

They measure the same thing: the maximum level your signal reaches.

Using either is fine,

but if you have a choice technically True Peak is more accurate

RMS and LUFS

Integrated (Average) Loudness Measurements

RMS

the average loudness level of your signal over a given time period using the average power of the signal

LUFS: the average loudness level of your signal over a given time period based on human perception of loudness.

As we know: both RMS and LUFS are integrated loudness meters. This means that they measure loudness over a period of time. The difference is how they measure loudness:

RMS: judges loudness based on the voltage of the signal.
LUFS: judges loudness based on how humans perceive loudness.

I bet that you can guess which one is better.
Yep, it’s LUFS. It’s the industry standard, and for a reason.

Since LUFS measures average loudness based on human perception of loudness, it gives us a more accurate representation how loud our listeners will judge the loudness of our tracks. This perceived loudness is what we care about. Our listeners aren’t going to be putting metering plugins on our tracks to judge loudness, they’re going to be listening to them.

It’s worth mentioning again: LUFS is the industry standard. This alone is another reason to use LUFS. It will be more seamless when preparing tracks to send to streaming services and other platforms if you’re making mix decisions based on LUFS measures. Don’t worry: if you only have access to an RMS meter, that’s fine. A LUFS meter and an RMS meter will give you very similar readings. But if you have an option, I would use LUFS.

The Loudness Wars
The loudness wars are over. It’s settled. The streaming platforms ended them – this is how:

We know that LUFS measure the average volume of a song over time. What the streaming platforms did was implement a maximum LUFS reading for your track as a whole. As part of the submission process, these services will run your track through their LUFS meter and turn it down if the LUFS level is too high. Thus, there’s no incentive to make your track as loud as possible; the streaming services will just turn it down.

Here is each platform’s maximum LUFS limits:

Best Metering Plugins
Now we understand the difference between Peak, True Peak, RMS and LUFS, and we know exactly how loud to make our masters for export to the major streaming services. Now it’s time to get ourselves a metering plugin, start measuring our loudness, and use that information to make better decisions in our mix

The following are (in my opinion) some of the best options:

Youlean Loudness Meter 2 – best free option

ADPTR AUDIO Metric AB – amazing referencing tool that has metering built in. I love this thing.

Waves WLM Plus Loudness Meter

FabFilter Pro-L – a amazing limiter that has a ton of metering tools built in

LEVELS by Mastering in the Mix

www.pianoforproducers.com /loudness/

The Difference Between Peak, True Peak, LUFS, and RMS:

How to Measure Loudness for Spotify, Apple Music, YouTube and Tidal –

Piano For Producers

5-7 minutes

*in ‘acoustix’, ‘loudness’ is the ‘subjective perception’ of ‘sound pressure’*

More formally, it is defined as,

“That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud”

The relation of physical attributes of sound to perceived loudness consists of physical, physiological and psychological components. The study of apparent loudness is included in the topic of psychoacoustics and employs methods of psychophysics.

In different industries, loudness may have different meanings and different measurement standards. Some definitions, such as ITU-R BS.1770 refer to the relative loudness of different segments of electronically reproduced sounds, such as for broadcasting and cinema. Others, such as ISO 532A (Stevens loudness, measured in sones), ISO 532B (Zwicker loudness), DIN 45631 and ASA/ANSI S3.4, have a more general scope and are often used to characterize loudness of environmental noise. More modern standards, such as Nordtest ACOU112 and ISO/AWI 532-3 (in progress) take into account other components of loudness, such as onset rate, time variation and spectral masking.

Loudness, a subjective measure, is often confused with physical measures of sound strength such as sound pressure, sound pressure level (in decibels), sound intensity or sound power. Weighting filters such as A-weighting and LKFS attempt to compensate measurements to correspond to loudness as perceived by the typical human.

Explanation[edit]
The perception of loudness is related to sound pressure level (SPL), frequency content and duration of a sound.[2] The relationship between SPL and loudness of a single tone can be approximated by Stevens’s power law in which SPL has an exponent of 0.67.[a] A more precise model known as the Inflected Exponential function,[3] indicates that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels.[4]

The sensitivity of the human ear changes as a function of frequency, as shown in the equal-loudness graph. Each line on this graph shows the SPL required for frequencies to be perceived as equally loud, and different curves pertain to different sound pressure levels. It also shows that humans with normal hearing are most sensitive to sounds around 2–4 kHz, with sensitivity declining to either side of this region. A complete model of the perception of loudness will include the integration of SPL by frequency.[5]

Historically, loudness was measured using an “ear-balance” audiometer in which the amplitude of a sine wave was adjusted by the user to equal the perceived loudness of the sound being evaluated. Contemporary standards for measurement of loudness are based on the summation of energy in critical bands.[6]

Hearing loss[edit]
When sensorineural hearing loss (damage to the cochlea or in the brain) is present, the perception of loudness is altered. Sounds at low levels (often perceived by those without hearing loss as relatively quiet) are no longer audible to the hearing impaired, but sounds at high levels often are perceived as having the same loudness as they would for an unimpaired listener. This phenomenon can be explained by two theories, called loudness recruitment and softness imperception.

Loudness recruitment posits that loudness grows more rapidly for certain listeners than normal listeners with changes in level. This theory has been accepted as the classical explanation.

Softness imperception, a term coined by Mary Florentine around 2002,[7] proposes that some listeners with sensorineural hearing loss may exhibit a normal rate of loudness growth, but instead have an elevated loudness at their threshold. That is, the softest sound that is audible to these listeners is louder than the softest sound audible to normal listeners.

Compensation[edit]
The loudness control associated with a loudness compensation feature on some consumer stereos alters the frequency response curve to correspond roughly with the equal loudness characteristic of the ear.[8] Loudness compensation is intended to make the recorded music sound more natural when played at a lower levels by boosting low frequencies, to which the ear is less sensitive at lower sound pressure levels.

Normalization[edit]
Loudness normalization is a specific type of audio normalization that equalizes perceived level such that, for instance, commercials do not sound louder than television programs. Loudness normalization schemes exist for a number of audio applications.

Broadcast[edit]
Commercial Advertisement Loudness Mitigation Act
EBU R 128[9]
Movie and home theaters[edit]
Dialnorm
Music playback[edit]
Sound Check in iTunes
ReplayGain
Normalization systems built into streaming services such as Spotify and YouTube.
Measurement[edit]
Historically Sone (loudness N) and Phon (loudness level LN) units have been used to measure loudness.[10]

A-weighting follows human sensitivity to sound and describes relative perceived loudness for at quiet to moderate speech levels, around 40 phons.

Relative loudness monitoring in production is measured in accordance with ITU-R BS.1770 in units of LKFS.[11] Work began on ITU-R BS.1770 in 2001 after 0 dBFS+ level distortion in converters and lossy codecs had become evident; and the original Leq(RLB) loudness metric was proposed by Gilbert Soulodre in 2003.[12] Based on data from subjective listening tests, Leq(RLB) compared favorably to numerous other algorithms. CBC, Dolby and TC Electronic and numerous broadcasters contributed to the listening tests. Loudness levels measured according to the Leq(RLB) specified in ITU-R BS.1770 are reported in LKFS units.

The ITU-R BS.1770 measurement system was improved for made multi-channel applications (monaural to 5.1 surround sound). To make the loudness metric cross-genre friendly, a relative measurement gate was added. This work was carried out in 2008 by the EBU. The improvements were brought back into BS.1770-2. ITU subsequently updated the true-peak metric (BS.1770-3) and added provision for even more audio channels, for instance 22.2 surround sound (BS.1770-4).