Our best measuring tool: our own ears?

A special sense

Now the purpose of this article is not to directly compare our ears to our eyes. Although it is interesting to put these senses side by side, because humans rely so incredibly on sight. And that while our ears can register with such unprecedented accuracy. Also, in a sense, hearing is still a great mystery to science.

For example: we know that we can localize sound sources by a difference in timing between the left and right ear (ITD: interaural timing difference). Suppose there is a timing difference of 600 microseconds between the left and right ear (we can detect timing differences of up to 10 microseconds). Intuitively, we then know that the sound is on the left and we effortlessly turn our head toward the source. We can do this with our eyes closed. Nothing special about that, right?

Well, yes there is. Because according to science, it takes about up to a millisecond for the signal to reach the brain. And since our brains actually “hears” for us (the ears and the system behind them only transmit the signal, the brain processes it), this should not be possible. Let alone with a difference of only 10 microseconds! Even science still thinks this is something special and does not yet know exactly how this works.

The fact that we can localize so unprecedentedly accurately – phase sensitivity thus – does explain why speaker placement, timing and phase correctness in a hi-fi system is so incredibly important!

Then another special phenomenon: experiencing sound without hearing it. There was an experiment done in 2003 at a London concert in which scientists mixed 17 Hz infrasonic sound with a few songs. Afterwards, the audience was asked what they experienced. About 22 percent of those surveyed reported feelings of discomfort, anxiety and other strange sensations. So although we don’t hear it “directly,” we do notice it. Incidentally, this phenomenon is now common knowledge. People often do not respond well to ifrasound: we usually become uncomfortable.

Moving in the other direction, we come to ultrasound. Human hearing goes up to 20 kHz. So why do manufacturers produce speakers with a range well above that? This has mainly to do with distortion – ringing.

However, there are also super tweeters that play from about 15 KHz and can also go much higher than 20 KHz. And many enthusiasts report that the effect is very audible. We have also experienced this. Perhaps the fact that we don’t hear it directly, but we do notice it, also plays a role here. (Bone conduction?)

What also came to mind after reading some literature is that the ear can unravel complex signals with the greatest of ease. Go figure: we recognize the voice of our friends and family with the greatest ease. Or the timbre of an instrument. And we can do the same in noisy environments where the eardrums are bombarded with countless other vibrations. Think of a restaurant, busy road or during a concert.

Distinguishing instruments, for example, we do so by recognizing – or analyzing with the brain – the myriad harmonics that an instrument creates. If a guitar or violin were both to play one tone of 400 Hz, it would be very difficult to distinguish. But because of the numerous harmonics (800 Hz, 1200 Hz, 1600 Hz, etc.) that these instruments produce, the 400 Hz tone has body, air and character and we humans can hear what kind of instrument it is (every instrument does this differently). And maybe even the brand and type (material, shape and size play a role).