This is part 2 in our series of audio illusions.

The binaural beats is one of the most researched audio illusions. It has been talked about by people in the medical fields because some believe that this illusion can help the mind and body relax. For this reason, there are people who use this as part of their meditation and wellbeing practices. With that said there is still lots of research to be done in order to prove any claims.

How to Create Binaural Beats

To create this audio illusion you need to have two different frequencies. These two separate frequencies must be played with one in the left ear and the other in the right ear. When you do this a third pulse will be heard at a frequency that is the difference between the two main frequencies.

For example, if you have a frequency of 300 Hz in one ear and a frequency of 310 Hz in the other ear you will get a third at 10 Hz.

Have a listen for yourself

How it Works

Part of this illusion comes from how the brain processes sound. It is normal for our brain to measure the difference a sound takes to reach each ear. This is how we know where a sound is coming from. When a sound reaches your left ear first you know that sound must be coming from your left side. The important part to remember is that this processing is very precise.

It’s also important to remember that we perceive sound as a time based medium. Now, because our brain analyzes sound simultaneously from both ears when a sound that is pure but differs by a few Hertz it tends to process the sound as if it is changing its location causing an imaginary third tone to sound.

Questions? Post them in the comments section and Stay tuned for our next audio illusion.

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.

Missing Fundamental

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.