Fletcher Munson Curve: Easily Understand in 5 Minutes

Fletcher Munson Curve Quickly Explained

The Fletcher-Munson loudness curve is a graph that indicates the human ear’s sensitivity to different frequencies at various levels.

This Means:
  • At low listening volumes, the mid-frequency range sounds more prominent, while the low and high frequency ranges appear to fade into the background.
  • At high listening volumes, the lows and highs become more prominent, while the midrange appears softer.
If you are mixing, you want your mix to sound the best at it’s loudest volume.
And you want to track a certain volume you listen to your song at and remember it as a benchmark.

The more in-depth explanation begins now…

The Ear

The human ear detects pressure variations in the surrounding air particles, picking up vibrations of the air molecules and converting them to sound.

The mechanism is as follows:

  1. Sound waves enter the ear canal and exert varying pressure on one side of the eardrum; the air on the other side of the eardrum is resting at your heads internal pressure.
  2. The pressure difference between the two sides causes the drum to vibrate, which causes your ear bones in the middle ear known as the ossicles to oscillate.
  3. This oscillation is eventually transmitted to the fluid-filled inner ear, where the movement of the fluid disturbs hair cells, which send nerve impulses to the brain. And voila you are hearing. And your brain computes this data along the fletcher-munson curve.

Not All Sound Is Perceived Equally

Interestingly enough, your brain has evolved to detect the different frequencies at different thresholds of loudness

Fletcher Munson Curve
The Blue Line is the Fletcher-Munson Curve, Notice how you are not sensitive to lower frequencies until around ~80 dB range

Because the ear is more sensitive to lower frequencies at higher sound pressure levels, the low-frequency lines flatten out. Take note of how the ear becomes less sensitive to frequencies above 6,000 Hz. This is because your ear is generally attuned to the ranges of human speech, (and animal noises) as that’s what it mainly evolved to hear. 

The Fletcher Munson Curves explain why quieter music appears duller, and less pronounced than louder music. 

The louder the music, the more we perceive the lower frequencies, making it more full and rich. Many stereo systems include a loudness control that boosts the sound’s low and high frequencies.

Take Away

  • The Fletcher-Munson Curve shows the difference in loudness thresholds involved in pitch perception 
  • Lower frequencies, generally, require higher volumes to be heard
  • Mid-range frequencies are the easiest to pick-up
  • Higher range freqeuncies are slightly less pronounced than the mid range

Mixing (Physics Student’s Can Now Leave)

So if you mix music, you have probably picked up on the problem the Fletcher-Munson curve creates. If you listen to a song/project quitely, and then listen to it at MAX volume you are going to go crazy trying to EQ it, because it sounds different at both levels! 

No you are not crazy… this is the Fletcher-Munson Curve in action. So to mix to the best of your abilities you are going to want to do any of your volume control/EQ/ anything that relies on you detecting the loudness of a sound, at the same level. So go write down that level and keep it as the benchmark to test when you come back after a days rest. 

You may wonder: Why do I tend to have that benchmark at a loud volume, as suggested earlier in the article? Because people pay attention to music when it is at it’s loudest.

Do you pay attention more to music when its loud or when it’s quite?

Do you pay attention to music more at a concert, or when someones ringtone goes off?

When you demo music, do you play it back softly, or loud?

Human’s like loud things, and so we sometimes equate louder as better, hence the loudness wars. So when someone wants to listen and pay attention to your song, it is at a louder volume. And that is why you should be mixing at a louder volume!

Conclusion

I hope you learned something about the Fletcher Munson curve! What it is, and what to do about while mixing. Thank you for reading, and good luck mixing!

Parlours Music

Hedrich and George!

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