How Our Ears Sense the Direction of Sounds | Humans Developed this Essential Skill

Haven’t you ever wondered….

When you hear a sound, and you instinctually turn your head toward that sound….

How do you know where it comes from?

This incredible hearing ability is one that we use daily, both in music and in real life.  Yet few people understand how it works.

And so today, I will show you.

But first…

Why Humans Developed this Essential Skill

Our ability to perceive sound direction works through a process known as binaural hearing, which essentially means “hearing with two ears”.

Through the course of evolution, it turned out that this was the system most effective at allowing animals to gauge the direction of sounds in their environment.

And it’s obvious why this skill is important…if a predator is hunting you, you need to know where it is, so you can run away.

That’s how it helped us survive back then, and how it continues to help us today.

What’s less obvious is why you, as a recording musician, should care…

So I’ll tell you.

How this Knowledge Applies to Your Music

We all want to create better mixes for our recordings, right?

Well a big part of creating good mixes is strategically placing each instrument at various positions within the sound field.

Some instruments panned in the center, others off to the side.  Some instruments up close, others off in the distance.

But while each instrument might sound-like it originates from a unique point, in reality, they all come from the same place: your studio monitors (or headphones, of course).  In other words…they are just illusions.

If you want to create good illusions in your mix, you need to know how to fool your ears.  To do that, you must understand how they interpret information.

So here’s how it works…

How Our Ears Judge DIRECTION

The secret to binaural hearing is the location of the ears.

Because they are on opposite sides of the head, the sounds heard by either ear will vary in timing, volume, and frequency balance.  These differences are the clues your brain uses to decode a sound’s location.

Let’s use an example:  Imagine an unidentified sound that originates directly to the left of your head.

Here’s how your brain interprets each clue:

1. Variations in Timing

When a sound comes from the left, the travel distance to your left ear is slightly shorter than the travel distance to your right ear.  So the left hears it milliseconds before the right.

This is your brain’s first clue that the sound might be coming from the left.  But that information alone is not enough.  It still needs more.

The next clue is…

2. Variations in Volume

As we all know, sound gets softer as it moves further away.  Sound also gets softer when there are objects blocking it.

If our unidentified sound is coming from the left…

It will also sound a tiny bit softer to your right ear since it’s further away.  And it will sound softer still, since your head is blocking it.

Now your brain is even more certain it’s got things figured out.

But there’s just one more thing…

3. Variations in Frequency

As we’ve just covered, when a sounds comes from the left, your head blocks a portion of it from reaching your right ear.  What you may not know, is that it DOESN’T block all frequencies EQUALLY.

High frequencies have less energy, are more easily absorbed by obstructions than low frequencies.  So with our unidentified sound, your right ear will get MORE of the low end, and LESS of the high end.

This is the final clue.

When all 3 of these clues match up…your brain is certain of what it hears.  Because in nature, these 3 clues ALWAYS line up.

When they DON’T match up (such as in a mix, where they can be manipulated) your brain gets confused and is uncertain of the sound’s location.

Now at this point, you may be asking a question…What happens if the sound is directly in front of you?

Think about it…

• The timing would be the same in each ear
• The volume would be the same
• The frequency would be the same

And the same would also be true if the sound were directly behind you.  Yet somehow when it happens in real life, you can clearly hear the difference, right?  WTF?

Now here’s where it gets SUPER INTERESTING….

Whenever this happens, your brain is momentarily confused.  So it triggers an instinctual response for you to turn your heard to the side ever so slightly.

It’s so fast and subtle, you won’t notice it even if you try.

This slight head turn creates enough of a difference in the sound heard by each ear to allow your brain to figure out where the sound is coming from.

Fascinating, HUH?

So that’s how it works with judging direction.  Now let’s talk about judging distance.

How our ears judge DISTANCE

When your brain judges the distance of a sound, it relies less on binaural hearing, and more on the following 3 clues: the frequency response, the amount of reverb, and the amount of pre-delay.

Let’s looks at these clues in more detail.

1. Amount of Reverb

Most of us already know…the farther the sound, the more reverb it has.  But here’s why:

That “reverby” character of far-off sounds exists because almost none of the sound reaches you directly.  Instead, almost all of it reflects off multiple surfaces before ever reaching your ears.

This is your brain’s first clue that a sound is far away.  Here’s the next one:

2. Pre delay

For those of you who aren’t “reverb nerds”, pre-delay is the time gap between the first arrival of direct sound, and the first arrival of reflected sound.

In an environment with lots of reflective surfaces, sounds heard from up close may still have a lot of reverb, but the time gap between the directed sound and reverb will be large.

Far-off sounds have a shorter pre-delay time, because BOTH sounds have to travel a great distance to reach you.

That’s the second clue.  The last, and perhaps most important clue is…

3. Frequency Response

When a sound travels far to reach you, much of its high frequency detail dissipates along the way.

Here’s why:

Like we covered earlier, high frequencies carry less energy than low ones, so they are more easily absorbed by objects in the environment.

Over long distances, obstructions such as land masses, buildings, and even air in the atmosphere all contribute to squash those high frequencies.

This is the final clue.  At this point, when all these clues align, your brain is quite certain of what it is hearing.

Now What?

Now that you know this stuff, let it digest for a while.  Take notice of the various sounds around you, both in real life, and in music.

• Where are they coming from?
• What qualities do you hear?
• And what are your ears and brain doing to connect the dots?

Think about it until it becomes internalized.  You will be a better musician for it.