Posted by: soundlounge | July 29, 2009

How The Shape Of Our Ears Affects What We Hear

pinna

The wrinkles and folds of our ears aren’t just bizarre and useless vestiges like human tailbones, webbed feet, wisdom teeth, or appendixes. In fact, complex outer ears like ours are an evolutionary breakthrough. You won’t find protruding ears on less-developed creatures like fish and lizards. Human ears, on the other hand, are complex sound-catchers. The odd bulges and crevices of the pinna (the visible part of the ear) are designed to amplify sounds relevant to humans, especially the sounds of speech. As Robert Jourdain explains in Music, the Brain, and Ecstasy, “Our pinnae are too small to reflect the long waves that constitute low-frequency sound; they boost only high-frequency components…those most important for speech.” Thanks to the logic of Mother Nature, the sounds we produce when speaking are the same sounds we can hear the best.

Along with our enhanced perception of speech, our perception of music is also influenced by our ears’ slight bias towards higher-frequency sounds. To our ears, a high-pitched piccolo may seem to cut through the orchestra more easily than a low-pitched tuba. Because of their high-frequency-boosting shape, our pinnae make music sound slightly “sweeter,” according to Jourdain. This is true of recorded music as well as live music.

One common misconception of recorded music is that microphones are used exactly like our ears to capture sound. However, unlike our ears, most recording microphones are designed to capture a broad range of frequencies equally well. This allows the music to be played back on speakers with all its natural sounds intact. Our ears then filter the sounds just as we would at a live concert.

in-ear headphonesBut what happens when we completely skip our pinnae and stick earbuds or in-ear headphones straight into our ear canals? Naturally, the sound changes. Our pinnae no longer amplify the same high frequencies they would when listening to the music through speakers or on-ear headphones. So in theory, music piped straight through to our ear canal will sound a bit duller than music that gets reflected through our pinnae.

In reality, though, no pair of headphones or set of speakers recreates live music perfectly, with all frequencies intact. So the average music listener does not consciously perceive this slight frequency difference due to these pinnae reflections. Only the most obsessed audiophile would claim that a lack of pinnae reflections makes music less enjoyable.

Radiohead's Thom Yorke and a dummy head for binaural recording

Radiohead's Thom Yorke and a dummy head for binaural recording

On the other hand, some imaginative audio engineers have begun using the unique shape of our ears to reinvent the recording process and create incredibly realistic listening experiences. Instead of using traditional microphones, they place two small microphones inside the “ear canals” of an artificial human head. They can then place this “dummy head” anywhere inside a concert hall, even in the middle of an orchestra. The resulting recording will be the sum total of all the sounds from the orchestra bouncing through the dummy’s pair of “ears” and into the microphones. Because of the stereo effect and the natural ear reflections recorded by these dummy head microphones, the listener will feel transported to the concert hall, hearing the orchestra in 360 degrees around his or her head. Expect this eerily-realistic effect (known as binaural dummy head recording) to be used in more and more recordings.

Listen with in-ear headphones to this binaural audio sample from the Wikimedia Commons:

The dummy head recording method was used in this Revolt music video:

Charlie McCarron
Sound Consultant
soundlounge

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