So in order for us to completely understand the answer to this question, (Why our recorded voice sounds different when we hear it?) we need to first understand how the ear works.
Let’s breakdown how the ear works in an extremely simple way. We won’t dive too much into the intricacies of the individual parts of the ear, but just how they function and what purpose they serve.
The ear in a broad sense is divided into 3 parts:
As you can see the sound waves generated from a source travels as a number of compressions and rarefactions. These can also be viewed as a minute pressure difference between the two points as shown in the image below.
The ear is essentially a device that converts this pressure difference into something we perceive as sound. How it does this is magnificent and very very interesting.
So the sound waves generated from a source travels towards the ear, then the outer ear where the energy gets focussed by the shape of the ear and then hits the eardrum. You can think of the eardrum as a tiny membrane that moves back and forth, replicating or rather converting the physical energy of the movement of the compression and rarefactions into biological movement.
This membrane, in turn, is connected to a bone mechanism which moves as the membrane moves; these bones are a part of the middle ear. The movement of this bone, in turn, sets the fluid in the inner ear in motion causing the hair cells to move. This movement of the hair cells creates an electrical impulse which is transmitted to the part of the brain that decodes this electrical signal into what we perceive as sound.
This complex system is how we hear the sound, our ear has gone through millions upon millions of years of evolution to create this version of the ear. Maybe a million a year from now our ears might be quite different.
Now let’s come back to the question of why our ears sound different when we hear ourselves in a recording.
Here comes the fun part of our discussion! Our ears also hear sound through something called bone conduction.
You see this part of our ear which just out, this is the bone
This is the same bone that we referred to in the earlier paragraph. This bone conducts any sound and converts it into electrical impulses that our brain again perceive as sound.
When we talk, the sound is generated through our vocal cords and transmits outward from our vocal cords. In the process this sound is also internally conducted through the bone in our ear internally from the vocals chords, this sound that is conducted through our bone is perceived to be much lower in pitch.
When you hear a recording of your voice, you no longer hear the deeper tone provided by bone conduction. This is the reason your voice sounds different when you hear it recorded.
In fact, there was a recent study that showed that having double protection of the eardrum is not enough. There are multiple cases in which bone conduction caused severe hearing damage in some individuals.
You might have seen Bone conduction earphones that have become mainstream lately, they work by placing a diaphragm on the bone and conducting the sound through it instead of the approach of using earphones inserted into the ear.
Interestingly though, if you think about it Beethoven was the first one to find out about bone conduction. Since he was deaf, i.e has a ruptured eardrum he could hear the sound of the piano by biting down on it and conducting that sound through the ear bone.