Audio Illusions – Missing Fundamental
The world you an I live in today is a one that uses visuals to express meaning. We’ve relied on signs and graphics for many years. In fact the words you are reading right now are signs.
Visual meaning is great and it’s quick particularly if you are awake. It’s rather hard to see when you are sleeping. You’re ears however keep pulling in information all day long from before you are born to the day you die. Because of this evolutionary fact our ears are quite perceptive and can’t be easily deceived. This is why we have many visual illusions but very few audio illusions.
Over the next few weeks, let me share with you some of the audio illusions in a hope you’ll get a better understanding of how sound works. This week lets look at the Missing Fundamental illusion.
All sound creates a vibration in the air. For musical instruments these vibrations happen as regularly repeating vibrations in an up-down fashion or back and forth cycle. If one up-down cycle happens in one second we say it is 1Hz. This is also known as the frequency of a note. So, when a pianists plays a middle ‘C’ on the piano there are approximitly 262 up-down cycles per second or we can say middle ‘C’ has a frequency of 262Hz.
This isn’t the only thing we percieve when a musician plays a note on their instrument. We also hear what are known as harmonics. Harmonics for most people cannot be heard with distinction, they blend with the main note we hear. Harmonics are related mathematically to the note that we typically hear as the main note (AKA the fundamental note). All music instruments produce harmonics in different strengths and numbers and this is what makes each instrument sound the way it does.
To make this illusion work you need to play enough harmonics (through artificial means) above a note and the unplayed fundamental note will suddenly be percieved as the lowest note even though it is not played.
Here’s a short video on how the missing fundamental sounds.
Alright, that’s all for today. Check back to learn about other audio illusions.