Guide to The Fletcher Munson Curve

The Fletcher Munson Curve

Have you ever heard a quiet, unfamiliar song and turned it up to find that you have listened to it a dozen times?

Some songs can sound very different when you change the volume. Today, we will be looking at what exactly causes this event to occur.

A certain process happens in the human brain that can change the way we perceive sounds. 

The Fletcher Munson Curve is not a widely known phenomenon. However, knowing about this curve can greatly impact the quality of audio you produce. 

Even if you don’t see yourself as a professional audio mixer, you will benefit from this as an amateur or even hobbyist mixer. 

Today we will be explaining what the Fletcher Munson Curve is and will teach you how to read the graph properly.

We will cover why you should care about the phenomenon and how to apply it to your everyday mixing. 

By the end of this guide, you will be producing top-notch audio that will blow everybody’s expectations. Let’s get started. 

What is the Fletcher Munson Curve?

What is the Fletcher Munson Curve?

The Fletcher Munson curve is a graphical representation of how humans perceive sound. More specifically, it shows a certain phenomenon that occurs when we hear music.

Depending on the music’s frequency, the perceived volume from our perspective is different from the music’s actual volume level. In other words, the music’s volume will change at a different rate in our minds compared to the recorded music. 

For instance, when you are listening to a song at low volume, you will hear mid-range frequencies more easily.

The high and low sounds will seem to fade in the background and will be more difficult to hear.

On the other hand, when you are listening to a song on high volume, you will hear high and low sounds more easily. The mid-range sounds will be harder to hear. 

Even though certain sounds appear to be higher or lower than others, the overall volume still stays the same, regardless of what you think you hear. This phenomenon is the Fletcher Munson Curve. 

The Fletcher Munson Curve has become one measurement out of many that are called equal-loudness contours. The contours measure how people perceive different frequencies and volumes. 

How The Human Ear Perceives Sound

The perception of sound changes with a change in volume and this phenomenon is majorly regulated by the internal structure of our ears. 

It’s essential to know how exactly our ear works in this case:

  • Our ears perceive sound through changing air pressure. When a soundwave approaches our ears, it alters the pressure outside our ear canal.
  • On the other hand, the air on the other side of the eardrum is at normal atmospheric pressure. The difference in air pressure leads to an imbalance and sets the eardrum in motion. 
  • The oscillation further disturbs the inner ear fluids, which stimulates the hair cells present in your ears. These hair cells transmit the message about the presence of a sound to your brain. We can see that it’s the vibration caused by the sound wave that determines how the sound is perceived.

Why Should I Care?

Why Should I Care?

Most people go through their entire life without knowing what the Fletcher Munson Curve is. However, if you are in the music industry, you will need to be familiar with this phenomenon. 

To create a high-end, professional-quality audio mix, you need to understand how the Fletcher Munson Curve works. Even if you are not a professional music mixer, any YouTuber, podcaster, or video editor can benefit from learning about the curve.

Understanding the curve is important because the phenomenon can introduce major problems while you are mixing. Misunderstanding the curve can also produce lower-quality music and audio. 

According to this phenomenon, if you mix the balance perfectly on one frequency, the perceived sound could change depending on how loud somebody listens to the music or video. 

For example, perhaps you are editing the audio at a higher volume one day. The notes in the mid-range seem too low, so you boost it up. When you listen to the mix at a lower volume, the mid-range sounds seem too high now.

This is the endless nightmare you could experience as an audio editor while dealing with the Fletcher Munson Curve. 

An audio mixer’s job is to create a balance of frequencies and volumes that will sound good to the listener at all volumes.

To do this, you need to use specific techniques that stem from the information we get from the Fletcher Munson graph. 

How Do I Read the Fletcher Munson Curve?

Understanding the phenomenon and reading the graph are two different things. At first glance, the graph looks very intimidating.

Not to worry – this section will review how to read the Fletcher Munson Curve in a few simple steps. 

Before we get into the steps of reading the graph, it will be beneficial to know what exactly you are looking at. The term “phon” describes how loud a sound is.

The sound pressure level is representative of the pressure of the sound, otherwise known as decibels.

Finally, the frequency measures the rate at which the sound changes direction. Frequency is measured per second. 

  1. The first thing you need to do is pick a certain phon level. Let’s pick the 60 phon curve, running from the top left to the right. 
  2. Now you will pick a frequency level. We will use 500Hz. When you have the frequency number in mind, follow the line until it intersects with your chosen phon level. 
  3. The last thing you need to do is draw a straight line from that point to the y-axis. You will arrive at a certain sound pressure level. The SPL value will tell you what the perceived decibel, or sound pressure level, is for the phon you chose. 

When you follow the line from the 500Hz to the 60-phon curve, you get around 58 decibels. This means that when the volume is at 60-phons, people will perceive a 500Hz noise as 58 decibels. 

The above explanation tells you how to read the graph technically. But what does it mean? 

Basically, at lower level phons, the curves on the graphs will have a higher range. This means that it will be easier to recognize different frequencies while mixing at moderate volumes.

On the other hand, the curves near the lower frequency levels are more bunched together. Therefore, it will be more difficult to distinguish different frequencies at low volumes. 

Real-Life Applications

Now that we know what a Fletcher Munson Curve is and how to read the graph, let’s look at the real-life applications of this phenomenon. 

As mentioned before, if you are into audio engineering at all, you should be acknowledging this phenomenon and adjusting how you edit music.

Using the graph’s information can increase the audio quality of youtube videos, podcasts, music, and any other media platform you use. 

If you want to take your media to the next level, there is a relatively easy solution to the Fletcher Munson phenomenon. 

Listen to the Audio on Different Speakers

Even though it will be impossible to monitor all frequencies in an audio file equally, there are still ways to get good results. 

The first thing you can do is to listen to the audio on different speakers. Some speakers will be more expensive than others, and most listeners will be playing the audio on mediocre speakers.

When you listen to the audio across different speakers, your music will be consistent. 

Have Different People Listen to the Same Audio File

The root of this problem is perception. To get a relatively stable music file across platforms, have different people listen to the audio. Ask what sounds stick out to them.

Find out if different listeners experience the music differently or if it sounds similar. 

Not everybody has to hear the same thing, but their feedback will shape how you adjust the levels. 

Mix the Audio at an Average Volume


The best way to create a steady, comfortable volume for all listeners is to mix the audio at an average volume. Mixing at around 80 to 85 SPL will be your best bet. 

After mixing it at that level, you can change the music to a higher volume and make small adjustments. You can also adjust the faders and equalizers in the 2-5 dB range. 

A critical step that you cannot forget about is changing the volume back to 80-85 dB SPL. After editing the audio at a higher volume, you need to make sure it still sounds good at the average mixing level.

Make the necessary adjustments if you edited the audio too much at higher volumes. 

After mixing and checking the mix at the higher levels, crank it down low. Make minor adjustments to the audio at the low volume.

However, you need to remember that any adjustments you make during this step could be three times louder when you put the volume back to normal.

That is why you should be very cautious when making changes at low volumes. 

If you follow these techniques, you will have a well-balanced and professional-sounding audio mix. 

The Problem With The Fletcher Munson Curve

If you want to produce quality music, then you need to know about the Fletcher Munson Curve. However, mixing the sound according to The Fletcher Munson Curve can be a huge challenge for amateur sound engineers.

Suppose you sit down to work on the EQ of a track, and you’re listening to it on a moderate volume. You feel that the lows and highs of the track could use a slight modification, and you do so based on the current volume. 

However, when you sit down the next day and listen to the same track at full volume, you realize that the highs and lows don’t hit the right tone. That’s because the volume change has changed how your ears perceive the sound. Now the question is, how do you fix the problem?

The Solution

The solution is pretty simple. It’s believed that people are only carefully listening to a song when they’re listening to it at the highest volume. 

For example, let’s assume you turned on the radio while getting ready for work each morning. Unless you’re hooked on a song, your attention is mostly on getting dressed. However, when your favorite song comes up, you’re likely to turn up the volume. That’s when the song has all your attention, and you carefully listen to each note.

It’s advised that you mix your track to sound the best at full volume. For this, you’ll need to work on the EQ at a high volume. Make sure the volume isn’t too high. It should be reasonably loud, but not deafening. 

You might worry about how the lows and highs will work in this case when you turn down the volume. The truth is, the lows and highs might drop a little when the volume is decreased, but that won’t be too bad on the listener’s ears. They’ll just need to turn up the volume. 

On the contrary, if the mix doesn’t sound well at the highest volume, the listeners are less likely to come back and listen to your track again.


The Fletcher Munson Curve is a graph that shows how humans perceive sound at different levels. It showcases a phenomenon where we perceive the loudness of a song differently than the actual volume. 

While most people won’t care about this, the curve is helpful for audio mixers to understand. If you create youtube videos, podcasts, or music, knowing about this phenomenon will help to produce a better mix. 

There are a few techniques you can use that will increase the quality of your audio mix. 

First of all, make sure to mix the audio at an average volume of 80 to 85 dB SPL. After editing at an average volume, make small adjustments as you play the audio at loud and quiet volumes. 

Finally, play the audio mix on different speakers. This will help accommodate the different platforms that listeners will play the audio on and create consistency. 


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