Fletcher Munson Curve: Everything You Need To Know

Fletcher Munson Curve: Everything You Need To Know

For most people recording in their home studios, understanding the Fletcher Munson Curve tends to be the most unexciting part of the process.

As a music enthusiast, you might be bouncing off the walls to start creating your own mixes as soon as you have bought the required gear.

But if you really want people to listen to your music or any other soundtrack for that matter, it’s crucial that you understand this oh-so-famous curve in acoustic engineering.

But what is the Fletcher Munson Curve, and why does it matter?

Well, the Fletcher Munson Curve is a hot topic amongst musicians because it illustrates an interesting phenomenon of human hearing.

If you are far from the geeks who find interpreting graphs and making complex calculations to be a rather enjoyable activity, looking at the Fletcher Munson Curve might make you feel dizzy. But there’s no need to worry.

We will explain the concept in the simplest terms so that you can leverage the graph in your own favor.

Want to improve your mixes and masters?

Let’s see how the Fletcher Munson Curve can help you in your music endeavors!

Fletcher Munson Curve – What Is It?

The Fletcher Munson Curve is a graphical representation of the fact that the actual loudness of a sound wave is different from the perceived loudness that your ears hear.

When the actual loudness of sound signal changes, the corresponding loudness that your brain perceives changes in a different manner depending on its frequency.

The Fletcher Munson Curve contains a set of graphs that show that when you listen to music at a lower volume, mid-range frequencies will be sound more prominent, whereas high and low frequencies will be somewhat suppressed.

However, when the volume is increased, the reverse happens – high and low frequencies become more pronounced while the mid-range frequencies fade into the background.

In other words, the Fletcher Munson Curve demonstrates the average sensitivity of a human ear to audio signals of different frequencies at varying sound levels.

What Are Fletcher Munson’s Equal-Loudness Contour Curves?

The terms Fletcher Munson Curve and Equal Loudness Contour Curve are often used interchangeably.

However, they don’t refer to one and the same thing. Although both graphs are plotted against the same quantities (sound level vs. frequency), there is a slight difference between the two.

The Equal Loudness Contour Curve is basically a more advanced version of the Fletcher Munson Curve.

The concept of how the way sound is perceived depends on its frequency and loudness level was first introduced in 1933 by American physicists, Harvey Fletcher and Wilden A. Munson.

Their findings were represented on a graph as a set of curves that were collectively labeled as the Fletcher Munson Curve.

It laid the foundation for setting industry standards for the design and manufacturing of all audio-related products.

However, in 1956, further research conducted by two scientists named Robinson and Dadson redefined the previous curves in a new manner.

This was eventually identified as the new benchmark for sound quality by the International Organization for Standardization in the ISO 226 standard.

Therefore, when it comes to improving mixes and masters, it’s better to refer to Equal Loudness Contours.

The original Fletcher Munson Curve is now considered to be a subset of the Equal Loudness Contour Curve.

The Equal Loudness Contour Curve illustrates the relationship between the frequency of sound and its loudness and the way these signals are received and then interpreted by your brain.

A Look at the Equal Loudness Contour Curve


Here is what the Fletcher Munson Curve (shown in blue) and Equal Loudness Contours (shown in red) look like:

Note that both curves show the responsiveness of ear to different frequencies at varying amplitudes.

The horizontal axis shows the frequency level in hertz (Hz), while the vertical axis denotes the sound pressure level (SPL) in decibels (dB).

All lines are plotted between 20 Hz and 20k Hz because this is the audible range for humans.

The key points that you need to pay attention to when it comes to the Equal Loudness Curve are as follows:

  • Low-frequency curves tend to flatten out as the loudness level increases. This is because, at higher volumes, the ear is more sensitive to low-frequency signals
  • All curves rise beyond 6,000 Hz because the ear is relatively less responsive to these frequencies. This is the main reason why soft music sounds less rich, even though the composer might have used instruments that should create an effect otherwise.

Does this all seem to be flying above your head?

If you are still having trouble grasping the concept of Fletcher Munson and Equal Loudness Contour Curve, we know the feeling.

Discerning between the actual and perceived loudness might not seem intuitive to you.

To get a better idea of how the curve related to the quality of sound when mixing, it would help to take a deeper look into the way our own hearing system works.

The Human Ear and How It Works

The main thing that you need to remember is that your ear has a different way of receiving different sounds at different volumes and frequencies.

Our ears work by sensing the variations in air pressure.

When a sound wave enters the ear canal, it exerts pressure on the eardrum.

Since the air on the other side of the drum is at atmospheric pressure, it creates a pressure difference, which in turn makes the eardrum vibrate. It transmits these vibrations to ossicles that are the small bones in the inner canal.

These vibrating bones then move special hair cells, which finally transmit the nerve impulses to your brain for further processing.

Here’s the interesting part:

The pattern of distribution of the hair cells in your ear is pretty much the same as the logarithmic scale used to measure sound levels on the Equal Loudness Curve!

In other words, although the whole ‘perceived vs. actual’ loudness concept on which the Contour Curve hinges is mostly physiological, a part of it is actually naturally built into our bodies.

Amazing, isn’t it?

Before we shed more light on the role of the equal-loudness curve in producing top-notch mixes, let’s take a look at another related concept – the House Curve.

What is a House Curve?

Why Does It Matter?

House Curves are often misinterpreted as the Fletcher Munson Curve, but in reality, that is not the case.

The most basic idea of a House Curve is pretty much the same as what the name hints at – it is an EQ setting that you use to make the speakers sound better in your ‘house’ or home studio.

EQ, which stands for equalization, refers to the process of balancing the different components of music by adjusting their respective frequencies in the recorded track.

A proper house curve should ideally have a downward sloping trend as the resulting audio is believed to sound most pleasing to the listener.

Why Does It Matter?

The million-dollar question that you might be asking is, ‘why does the Fletcher Munson Curve matter?’

Well, to answer that question, consider this scenario:

Imagine you are driving in the car and the radio’s playing in the back at a low volume.  A new song comes, and it seems to catch your attention, so you turn up the volume a little bit.

It sounds even better, so you crank it up all the way and the next thing you know you are humming it all day long. It’s become your new favorite.

That has probably happened at least once, right?

Now recall if the exact opposite has ever happened to you. You seem to like a song you have never heard before.

But when you turn up the volume, you realize it’s not that great and decide to switch the channel.

Do you want this to happen when someone’s listening to your mixes or any other soundtrack that you record? Definitely not!

This is where the Fletcher Munson and Equal Loudness Contours come to your rescue.

Of course, one might argue that if the music sounds good at a certain volume, why bother will all these complex graphs?

But what you need to remember is that as a composer, you actually want people to listen to your mixes at full volume. Don’t you?

Because that is when the listener is not just really listening to your music, but also loving every beat in it!

This doesn’t mean that you mix and master audio at a deafening level – you just need to make sure that the quality doesn’t deteriorate at higher volumes.

Wrap Up

The Fletcher Munson Curve and the concept of equal-loudness are of chief importance when it comes to producing quality music.

While the concept might indeed be difficult to comprehend, the good news is that you don’t really need to master the art of reading the curve.

As long as you know the basic idea of how low, middle, and high-frequency components dominate the overall audio at different sound levels, you are good to go.

Hopefully, this article would have helped you learn how to leverage the Fletcher Munson Curve in your favor.

Happy mixing!

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