Why are crying babies so damn annoying?
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Have you ever been on an airplane with a crying baby?
If not: you’re blessed.
I have yet to experience something more nerve wrecking than the furious screams of a seemingly cute ‘mini-human’, while taking the train to school, when all I want to do is listen to my own music.
But why are crying babies so annoying?
The answer to this lies partially within the nature of the human hearing.
Let’s assume that both an adult man and an infant are crying at the same sound intensity level. We might think that both will be perceived at the same loudness, hence the two should be equally annoying. But that’s just not the case. The mans voice will almost always sound quieter than that of the baby. This is due to the difference of frequencies (or pitch).
As we know, every sound we perceive is defined by its frequency. Whereas certain sounds, like the male voice, generally have a lower frequency, other sounds are significantly higher, like that of a crying baby.
To visually compare the two, a spectrum analyzer is used, which displays the intensity of all frequencies within the human range of hearing: 20Hz to 20,000Hz.
Now, when a typical male voice gets run through a spectrum analyzer, the result looks like this:
The orange peaks represent the frequency components of this vocal sample. Peaks on the right are higher in frequency than peaks on the left.
Notice the largest peak in the recording? (That’s where the arrow is pointing to)
That is the loudest frequency in this particular sample, which is exactly at 700 Hz.
So, if we were to put the baby’s screams into the spectrum analyzer, we get this:
Now, the dominant frequency is at a much higher 2700 Hz.
The reason why we perceive babies as being so damn loud is because of their high pitch.
Initially, this has been investigated by two scientists in the 1930’s. Harvey Fletcher and Wilden Munson discovered to which frequencies the human ear was most sensitive to. Their result was named the Fletcher-Munson Curve, or Equal Loudness Contour. Their findings were very similar to revised versions and are still applicable, especially in the higher frequencies.
The green line represents the Equal Loudness Contour. It’s shape shows how much energy is required to make a certain frequency sound equally as loud as a reference pitch at 1000 Hz. Therefore, it is named the Equal Loudness Contour, because every frequency along this line will be perceived at the same loudness.
We can see that the human ear is most sensitive to pitches between 2000 and 4000 Hz. Humans experience frequencies in this range as particularly unpleasant.
We can also see that the dominant frequency in the baby’s scream perfectly aligns with the trough of the Equal Loudness Contour, making it such an annoying experience.
Why are we sensitive to this frequency range?
On an evolutionary scale, the perception of crying babies was vital for the protection of one's family. Therefore, over an incredibly long time, our ears adapted to this, by shaping our ear canal to resonate at these specific frequencies, making them easier to hear.
Notice anything?
Have you noticed that the green line ends before reaching 20,000 Hz?
Why is that?
Well, most humans don’t hear past 18,000 Hz. Taking myself as an example, I am 17 years old and the maximum frequency I am able to hear is around 18,000 Hz. Everything beyond that would just be guessing, for me at least.
It’s perfectly normal that you don’t hear up to 20,000 Hz and to be honest; it doesn’t really matter anyway. Unless you’re a mixing or mastering engineer, it’s not crucial for you to hear such high frequencies.
However, you should be aware that your range of hearing gradually decreases as you age.
So, the reason why the Equal Loudness Contour stopped at around 17,000 Hz, is because participants physically could not hear beyond that point, independent of the loudness.
Applications of the Curve
Why do telephone connections sound ‘tinny’?
Have you ever thought about that?
There are many reasons to this, like the phone’s microphone or the data transmission and its limits, but in relation to the Equal Loudness Contour, transmitting and replicating frequencies below 100 or even 200 Hz requires a lot of energy. The same applies to frequencies above 3000 Hz. As these have to be amplified to sound equally as loud as frequencies at 2000 Hz, more energy is needed.
As vocal formats are based at 100 to 1000 Hz, it has been decided to focus on this essential frequency band, instead of transmitting and replicating the entire spectrum.
Hence, when you’re talking on the phone with your friends or family, you only hear an extract of their actual voice.
Maybe you will remember this at your next phone call. ;)
Want to learn more about loudness? Check out my other article about the Loudness War!
-Nico
