I have this Casio alarm clock for well over 25 years now. This alarm clock followed me from home to my new country in Perth Australia, and is a reliable workhouse - never fails to wake me up for all my exams and so on. Once I entered the workforce I’ve established a good biological clock routine and do not need for the use of a alarm clock again - but this clock stayed faithfully by my beside table till now.

The one feature this clock has is the EL backlight - high tech in it’s day, it’s something of a dated relic now with today’s OLED and backlit displays.

I love this clock, but there is something that annoys me always. There is this high pitched noise whenever the EL back light is lit. My curiosity is piqued when my wife commented she can only hear this noise when the clock is right by her ears, about 10 centimeters or more away she could not hear this noise any more. Definitely a no no when it’s more than 30 cm away. On the other hand, I still manage to hear this hum with the alarm clock an arms length away, possibly further. 

Via my phone app, the the tones of the hums - 2.8 kHz, 4.3 kHz and 7.1 kHz.

All three bands and its amplitude are well within the human auditory spectrum. And yet my wife cannot hear it while I can. Why? Do I have super ears? The answer sadly is no. 

People have the misconception that hearing is a pure physical activity - i.e. your hearing sensitivity is within the band of 50 Hz to 16.5 kHz (give or take). That is only half the story, because perception is cognitive (i.e. your brains is involved in understanding what you hear). In this example of EL backlight, I postulate that my wife has better hearing sensitivity (she can hear higher pitched tones than me), but I win on the cognitive side. My wife’s brain will automatically filter out the above 3 bands as background noise, while my brains don’t.

One of Sherlock Holmes favourite quote comes to mind:

You see, but you do not observe. The distinction is clear.

Something very similar is happening with our auditory senses too. “See” is akin to how sensitive our hearing is, while “observe” is akin to identify patterns within this sensitive range.

You hear, but you do not listen. The distinction is clear.

A lot of the arguments on the Internet (where the zealots often used the blind testing war cry to shut down any rational discussions) can be avoided if they understand this point.

If you have any EL back light device, give it a go - can you hear the noise? If you can already do this, you can go far with the hobby of high fidelity. If you cannot, put in enough hours to retrain your brains to spot for these patterns.

PS: Note that the EL light is just an example in this post. There are other things you can use to improve your active listening - e.g. clock ticks from a quartz timepiece, surface road noise, insect/bird calls. You are only limited by your imagination and hearing cognitive abilities.