Fletcher Munson Curve Explained

Fletcher Munson Curve Explained

You must have heard the saying “Music sounds better when it’s loud”.

While the saying is true, it is not exactly what you think it means.

To fully comprehend this saying, you need to know what the Fletcher-Munson curve is.

Not sure what it means?

Don’t worry. This post is for you.

Here you will get to know what the concept is exactly, who discovered it, and why is it widely used for mixing music.

As you get through the article, you will also learn that despite its wide application, it is far from perfect.

There are a few problems with this phenomenon but there are certainly ways to deal with them.

So let’s get started.

What is Fletcher-Munson Curve?

Effective Audio Interface

As you hear melodious music, it is far more than simple vibrations travelling through the air and into your ears.

As soon as the sound waves reach the ear, a complex process starts which converts the sound waves into a tune you can recognize and comprehend.

The Fletcher-Munson curve is a tool to evaluate how you perceive sound.

It is perhaps the most important discoveries of all times for music producers.

But even if you are not a professional, an understanding of this concept is critical especially if you want a good mix of music.

The Fletcher-Munson curve, also known as equal loudness contours, shows how a human ear perceives loudness at different frequencies of the sound waves.

So as the loudness changes, the perceived loudness experienced by our ears will change at a different rate which will vary according to the frequency.

So at low volumes, low and high frequencies become insignificant whereas frequencies in the middle range become more prominent.

Whereas at higher volume, the higher and lower range frequencies become more noticeable whereas the mid-ranged frequencies seem to fall in the background.

This striking difference is a result of how our ear responds to the sound waves.

The Mysterious Sense of Hearing 

Sense of Hearing

The human sense of hearing is indeed on of the most interesting phenomena to note.

The ear which is the sense organ plays a critical role by operating through variation in pressure.

As the sound wave enters the ear, it exerts pressure on the ear drum.

However, the ear is far more complicated on the other side. There the air is at atmospheric pressure.

This difference in air pressure on both sides of the ear drum results in the oscillation of three small bones located in the middle of the ear.

These bones are known as ossicles. The turbulence finally reaches the inner most part of the ear which is filled with fluid.

This results in motion in the fluid which disturbs the tiny hair cells located in the inner ear.

This tiny structure embedded deep inside the ear is responsible for sending brain signals and indicate that a sound is present.

However, an important aspect is that the ear can perceive sounds at a certain frequency.

Also, it is not equally sensitive to all frequencies within the audible range.

So equal pressure and amplitude, sounds at different frequencies will be perceived differently.

The curves reflect that at higher sound pressure, the ear is more sensitive to lower frequencies, so the music appears louder.

But it is less sensitive at frequencies 6,000 Hz and above.

So the louder the music, the ear perceives lower frequencies so the music appears more full and rich.

Now do you understand why “music sounds better when it’s loud”?

An understanding of Fletcher-Munson curve is critical because it allows music professionals to identify the exact level of loudness in the music which seems pleasant to the ears.

The use of this technology has allowed professionals to mix precise volumes to provide an excellent effect when mixing music.

Who Discovered it?

Honored Founder Of Curve

The Fletcher-Munson curve was part of an experiment performed by two researchers named Harvey Fletcher and Wilden A. Munson.

The experiment was originally intended to find the cheapest way to program a telephone call.

It was during this experiment that the two researchers recognized how the human ear perceives sound at various frequencies.

This discovery led to the recognition that the point at which the human ear hear all frequencies at their most equal in volume is somewhere around 90dB.

This is the reason why music professional work around mixing music to create a pressure close to 90dB.

This pressure is considered loud so creating music at this pressure gives an appealing sound to the ear.

The investigations of this experiment were published in the Journal of the Acoustical Society of America in the paper “Loudness: its definition, measurement and calculation” in 1933.

So what originally started as an investigation to find a cost-effective way of broadcasting a phone call, ended up being an important discovery for all music producers.

Problem With this Phenomenon

So while the Fletcher-Munson curve is a major part of music mixing and plays a critical role in making your sound pleasing or painful, the phenomena is associated with a few problems.

By looking at the Fletcher-Munson curve graph, you can get an idea of how the ear is going to perceive the sound at different frequencies, but when it comes to mixing music, you cannot predict the outcome unless you try it out yourself. This can be tricky.

As mentioned earlier, that higher and lower frequencies are more noticeable at higher volumes and mid-ranged frequencies are more prominent at lower volumes.

This is what brings in the challenge when using the Fletcher-Munson curve for mixing music.

If you edit a sound at a lower volume, mid-range frequencies will be more prominent so you adjust the high and low frequencies accordingly and the end result looks great.

But what if you increase the volume?

In that case what appeared to be pleasant is not appearing too much for your ears to handle.

So then again, you need to adjust the frequencies. This can be both tricky and frustrating for audio-recording professionals.

How to Deal with it?

Recording Music Equilizer

In an ideal world, where you simply use the Fletcher Munson curve graph, mixing music is simple.

But since the human ear is involved, you need to identify the ideal volume at which you can edit the sound.

As a general consensus, you should listen to the sound at a higher volume when editing or mixing.

Most music professionals agree that the ideal volume is between 75 and 85 dB.

At this intensity, the ear is most sensitive to the widest range of frequencies.

So at this range, you can create a great sound. However, individual differences in perceived volume will still exist.

Another important aspect to remember is that our ears can get used to a certain volume very quickly.

So if you mix music at an intensity of 80 dB and continue to do so for some time, eventually, your ears will get fatigued and this can affect your ability to create the perfect mix.

One of the best ways to avoid this problem is to break down your editing sessions into segments so that you can end up creating the right sound.

Another technique which can be used to improve the music mix on certain instruments is called the “Smiley Face EQ”.

The technique is based on the idea that by removing mid-ranged frequencies from certain instruments such as kick drum, you can create great mix simply by editing the high and low range frequencies.

This works because mid ranged frequencies are most prominent at lower volumes.

So when there is no mid ranged frequency, you will end up mixing sounds at a higher volume.

Though the technique is simple, it can create a disastrous mix if used incorrectly.

Also, it cannot be used when mixing sounds of different musical instruments.  

Conclusion

In all, the Fletcher-Munson curve is the most significant discovery for mixing musicand creating the perfect harmony between frequency and volume.

It is this phenomena which allows you to enjoy music at a sound which is perceived as pleasant and not as something terribly displeasing to the ears.

However, the idea is not perfect especially when you listen the sound at different volumes.

So for someone who is mixing music without the understanding of Fletcher-Munson curve can easily end up creating a sound which is perceived differently at various volumes.

But by keeping in mind the variations which is a result of different volume and listening the sound at higher volume when editing, musicians and producers can create a great sound with the right balance of frequency.

So the Fletcher-Munson curve is indeed one of the most significant discoveries of all times but to get the best results, you need to know how it works.

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