Timeline: Filling In The Gaps

Feb 4, 2019

Our ears and minds are amazing. Not only can they hear and experience the world around us, they are also filling in the gaps in our perception. We don’t even realize all the ways that our hearing is constructing the world around us, helping to keep us safe and understand our surroundings.

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In our last episode, we listened to some of the audio experiments discovered and championed by psychologist Diana Deutsch. The first set we looked at were tricks, asking us if we can trust our ears. Today we’ll look at some of the amazing things our sense of hearing can do. Once again I’m joined by some friends at VPR, Brendan Kinney, Leslie Blount and Joe Tymecki. I had them listen to this next experiment, called a constant spectrum melody.

James: What do you hear?

Brendan: Well, you had this overriding sound and then, it was almost like an organ or like a horn instrument doing some kind of notes in the background.

James: Can you sing the notes?

(Brendan sings)

(Joe Sings)

Joe: That’s all I hear, and then it sort of resets and goes again.

James: So, you just sang a melody.

Joe: Yes.

How about you? Did you hear a melody? Many people do. That sound, the constant spectrum melody, plays with timbre. There is just one pitch, one note, but the overtones, the harmonics, on top are being filtered and manipulated at a constant rate. The result of this manipulation allows you to experience a melody inside a single pitch.

Now, let’s try to hear a pitch that isn’t there at all. I’ll warn you this doesn’t work for everyone, but we’ll give it a try. This experiment is called the missing fundamental. You’ll hear the bass pitch “C”, the root, and then we’ll add harmonics on top. Listen as we remove the lower frequencies. You might still hear or at least feel the root pitch, the “C”, even though it’s not actually playing anymore.

Joe: Weird.

Leslie: I think it’s the physical feeling as much as anything.

James: And that’s the reality. It’s a physical feeling, a physical realization that if these frequencies exists than that one has to. But it’s not really there. It’s a phantom feeling that if these amount of frequencies are there than this must be the thing that’s causing them.

Leslie: Yeah.

Brendan: Yeah. That was an intense sound.

Here’s one more thing your ear can do and does all the time. Listen to this short piece of audio, but be warned it’s a little high and loud to make this work. Do you hear the tone rise smoothly despite the little buzzing interruptions? Listen again. Most people hear the tone continue without stopping, just with some added noise that their brain discards. Actually, those interruptions stop the sound. In reality there are three climbing pitches, but your brain holds the tone together to perceive it as one. We call this the illusionary continuity of notes.

By the way, your brain is doing this while you listen to me speak right now. The audio you’re hearing, my voice, whether through a podcast or on air, is digitized. This means it’s not a constant wave, like someone standing and speaking next to you. You’re listening to compressed samples being delivered to your ear at an incredibly fast rate and your brain is filling in the gaps while I speak. That is the power of our sense of hearing and the broadcast and recording industry are banking on this amazing ability.

What do you think? Did you hear a melody in the constant spectrum or experience the missing fundamental? We’d love to hear your thoughts on the power of your ears and mind.

Timeline is an exploration into the development of Western music.