Mastering Mixing Music Production

Loudness and Amplitude Explained: The Decibel, Human Perception and Units of Measurement

When working in the Pro Audio field, understanding loudness and its various units of measurement is very important.

When working in the Pro Audio field, understanding loudness and its various units of measurement is very important.

Being uneducated on the topic of loudness and amplitude has the capacity to hinder the modern Music Producer.

In this article we will attempt to cover all grounds on defining what loudness and amplitude are, the various units of measurements they have and its application to Dance Music Production.

Contents

  1. What Is Loudness?
  2. How Frequency Affects Loudness
  3. The Decibel, dBSPL and Logarithmic Scales
  4. Measurements of Loudness
Understanding loudness and the human perception of sound can drastically improve your mixing skills and help you to make informed decisions.


What is Loudness?

Loudness is defined as the subjective perception of sound pressure.

This means it is a measurement of how loud an individual experiences a sound to be, as opposed to the sound pressure level.

So loudness is a subjective measure.

It can often be confused with physical, objective measures of sound strength such as sound pressure, sound power or sound intensity.

Volume controls on our devices are calibrated to increase sound intensity logarithmically in order to provide users with what is perceived as a linear volume increase. Read on to find out why this is the case.

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How Frequency Affects Loudness

The human body is a carefully evolved and complex biological system, in which its auditory hearing has been adapted to provide sensory information to help with hunting, foraging, detecting threats or predators and communicating with other humans.

As a consequence, the sensitivity of the human ear changes as a function of frequency, this phenomenon is displayed by the equal-loudness graph below.

Each line on this graph shows the Sound Pressure Level that is required for different frequencies to be perceived as equally loud.

Each curve pertains to a different sound pressure level.

Source
Decibel levels perceived at 1kHz are also referred to as Phons.
Each curve is marked with a Phon number such as 60. This means it is the response for the sound level in which 1kHz was 60 dBSPL.

The graph teaches us some interesting things:

  • Normal unimpaired humans are most sensitive to sounds at 2-4 kHz.

    This corresponds to the same frequency band as human speech.


  • In order to perceive a 100Hz tone as being the same level as a 1kHz tone at a sound pressure level of 20dBSPL, you need to raise the 100Hz tone roughly 27dBSPL.

    This shows us how drastically our perception of sound changes with relation to frequency at low levels of volume.


  • Our sensitivity to sound level with respect to frequency changes depending on the sound pressure level.

    This is incredibly important to know. As a result of this, a mix will have a different balance at different levels of volume. Namely, lower frequencies (bass) will become significantly quieter at lower volumes. This is why you should always mix at the same volume, which should be at a suitable level to not cause any noise induced hearing loss. A control room level of 65-75dBSPL is advised.

A complete model of the subjective experience a human has of loudness (or their perception of loudness) should take into account both Sound Pressure Level (SPL) and frequency in order to be correct.

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The Decibel, dBSPL and Logarithmic Scales

Decibels are the perhaps the most common measurement of amplitude used in the modern day and understanding it is critical to understanding the nature of loudness.

The graph below features some common sounds and their approximate Decibel level.

Common sounds and their relative Decibel levels.
Numbers in the columns refer to the approximate dBSPL level of the sounds labelled across the bottom.

The Decibel is a logarithmic unit that expresses value in relation to another value, in doing so it mimics the human experience of loudness.

The dBSPL measurement, for example, refers to Sound Pressure Level and indicates a value relative to the Threshold of Human Hearing.

The human ear is capable of detecting sound pressure level over many orders of magnitude.

We also perceive these signals more or less on a logarithmic scale.

For example: A normal conversation at 60dB is not perceived as a thousand times louder than a whisper at 30dB.

Therefore, as the scale is logarithmic, the decibel is very useful for the following reasons:

  • An increase of 3dB equals a doubling in sound intensity, whilst an increase of 10dB equals a doubling in perceived loudness.

    This makes calculating the relative perceived volume of one sound to another much easier. If a normal conversation level of 60dB is compared to a traffic noise level of 70dB we can immediately see that the traffic is perceived as being twice as loud as the conversation.


  • The numbers are kept on human-sized scales.

    The human ear can astonishingly detect 10^13 units of sound pressure.

    By using a logarithmic scale with the Decibel, we get a scale of 0-130 dB, as opposed to a scale of 0-10000000000000 – which makes calculations much more difficult to deal with.

    0dB is the the quietest sound a human can hear, which is amazingly equal to 0.000002 Pascals of sound pressure.


  • It approximates the way our senses work.

    As mentioned before, human perception of sound has a roughly logarithmic response to the pressure level.

An increase of three decibels is approximately a doubling of power.
An increase of ten decibels is approximately a doubling in perceived loudness to humans.
Decibels are often used in measuring telecommunication signals.

Measurements of Loudness

If you are new to the world of Pro Audio, you might have seen a few abbreviations flying around that relate to loudness.

In the next few sections we will go over a few of the most important ones so that next time you see one, you will know what it means!

We will go over:

dBFS, LUFS, Integrated LUFS, Short Term LUFS, Momentary LUFS, LKFS, Dynamic Range (LU) True Peak Loudness and RMS.


The Decibel Full Scale Measurement (dBFS)

Within most modern DAWs, the sound level is measured in dBFS (DeciBel Full Scale), which differs from the traditional dBSPL scale.

The dBFS scale centres around loudness within a digital system.

0dBFS is equal to the absolute peak level allowed in a digital system before samples will become clipped.

When altering the level of instruments/tracks within your DAW (which is using the dBFS scale) you should expect the following to occur:

+/- 3dB A small change in loudness is perceived.

+/- 6dB A significant change in loudness is perceived.

+/- 10-12dB A doubling/halving of loudness is perceived.

Understanding the dBFS scale and how it translates to our perceived loudness will help you make more informed decisions during your mixing process and leave less to trial and error.

For example, you may listen to your mix and think your drums could definitely be twice as loud. So you know to increase the level by 10-12dBFS before you go to move the fader.

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Loudness Units relative to Full Scale (LUFS)

LUFS is a relatively new form of measurement and seen as the most precise way to measure loudness.

It was designed to create a standardised measurement of audio loudness that takes into consideration both human perception and electrical signal intensity.

As a consequence, the LUFS scale is used to set targets for audio normalisation for audio in cinema, TV, radio and music streaming.

Loudness is the most difficult factor to get consistently right when translating audio across a range of different forms of media/audio entertainment systems.

Integrated LUFS

Integrated loudness is a parameter for LUFS which is used to give a figure for the average total loudness across a period of time.

This is a way of standardising loudness for TV and Cinema where there is a lot of Dynamic Range between very loud and explosive action scenes and the quieter scenes where people might just be talking.

It might surprise you to know that Film and TV have strict standards for Integrated Loudness that are in fact set into the LUFS values.


Short Term LUFS

Short term LUFS is a way of measuring the perceived loudness over the last three seconds of audio.

This is useful for indicating areas of audio that are excessively loud.


Momentary LUFS

Momentary LUFS is a measurement that tracks the percieved loudness over the last 400ms of audio.

This is useful for displaying the current loudness in the moment of listening.


Loudness, K-weighted, relative to full scale (LKFS)

Let’s keep this one short and sweet because we have already explained what LKFS is.

LFKS and LUFS are identical, both terms describe the same phenomenon.

You will encounter LKFS when looking at loudness regulations for certain broadcasting unions.


Dynamic Range (LU)

Dynamic Range refers to the difference in loudness between the loudest and quietest parts of the audio in question.

LU is a means of measuring this difference is loudness and it uses the same perception based units to evaluate how loud something seems to humans.

LU indicated the difference between the quietest and loudest parts of audio over time in the same way that integrated LUFS does.

It uses the same increments as the dB scale, so 10 LU = 10dB.

An example of a measurement requirement might be: The audio must be ≀10 LU.

This simply means the difference in loudness between the loudest and quietest part of the whole piece of audio in question must be less than or equal to 10 dB.

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True Peak Loudness (dBTP)

True peak Loudness is measured in dBTP.

When we previously went over the dBFS scale used to measure digital audio levels, we established that 0dB is the highest possible sample peak that can occur before introducing distortion.

When converting Digital audio to analogue – a process that happens every time your computer outputs sound to your headphones/speakers from your DAW – something called inter-sample peaks can be created.

During the conversion process (from digital to analogue) a waveform is created by connecting the digital sample points together.

This sometimes causes the peak level to go past 0dB, which, as we know from before, introduces distortion.

These types of peaks are referred to as inter-sample peaks (learn more).

Loudness recommendations specify a maximum True Peak level, as opposed to a maximum Peak Level.

Like with integrated LUFS, there is a strict requirement for True Peak Loudness in TV Cinema and Radio.

True Peak loudness is useful to know about as a Music Producer, as understanding it can help to reduce the risk of distortion being introduced further down the line.

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Root Mean Square Metering (RMS)

RMS metering displays the average power of an audio signal.

It is considered to be close to what we as humans perceive as loudness.

As a consequence, it is seen by audio professionals as an accurate and useful way to determine the loudness of a mix.

RMS meters are modelled on analogue console VU meters which measure the power of the signal passing through their circuitry.


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