Typical Restoration

Typical Restoration

This chart shows a before and after of my own hearing. The before is my innate (damaged) hearing shown in the red (right) and blue (left) solid lines toward the top of the chart, the one with the colored balls on the curves. Everything between those curves and the threshold level marked as the green curve is lost to my everyday sense of hearing.

The orange line denotes the typical spectrum of comfortably loud music, which is approximately flat below 1 kHz, and then rolls off at about -6 dB/octave above that frequency. This is also a crudely typical amplitude spectrum for human speech, where all the non-vowel sounds live above the 1 kHz mark.

By plugging my headphones into a System 5000, a quick audiology test shows that my response transitions to the lower pair of red and blue curves. Of course it is not a perfect reconstruction. I'll say more about that in a moment. But notice now how much more hearing sensation is possible. Whereas, before I would find it impossible to hear any sounds at these musical intensities above 1.5 kHz, with the System 5000 I can hear quite well all the way up to the 6 kHz mark. Actually in listening sessions I am able to reach beyond that too.

Now why isn't it a perfect reconstruction of hearing, all the way to the green threshold level?

Humans deprived of sound cannot tolerate the brightness indicated by a full restoration. More typically our limit of tolerance for restoration is about 30% of our impairment. It is a bit like sitting in a dark room for a long time, and then suddenly going out into sunlight. It is simply too much.

So in reality, the physical restoration of hearing is not 100%, and cannot be tolerated to be such. We limit our maximum gains to no more than 24 dB, whereas, to reach full threshold it could require as much as 60-80 dB in many cases.

But there is a psychological aspect to consider as well. Living in a sonically dark universe, and then having some brightness restored, we immediately notice the little things that everyone else could hear if they paid attention... but they don't and we do because these sounds are foreign to our everyday world. So in that sense, we actually end up with a better sense of hearing than what was lost.

In the sense that a "Golden Ear" is most observant of subtle details, we do regain that ability by a huge amount. It is a combination of hearing a tolerable brightening of our world and the psychology of hearing really different sounds that don't normally exist in our world.

David McClain, Chief Technology Officer for Refined Audiometrics Laboratory