The Science of Sound, Part II

Welcome to Part II of the continuing series of the Science of Sound! If you missed the first lesson, you may want to click to go back and read so you're caught up.

I found a really neat site where you can play around with the different hertz levels, though be careful with your speaker volume if you go extremely high or extremely low. It's pretty entertaining to see how good (or not) your hearing really is. At the end of the post I'll include another link to a YouTube video that's a similar hearing test.

Today, we're going to talk about three topics:

-how hertz relate to a piano

-why do some notes sound good together, and others don't?

-what the heck is timbre?

Last time we learned all about hertz, and how they measure the pitch (highness or lowness) of a sound. Even if you don't have any experience in music, you probably at least know that each key on a piano plays a specific note (or pitch). Each note has a set hertz, since the hertz refers to how many waves per second the sound has. See below:

As you can see, each note has a set hertz. If you went and visited the hertz generator I mentioned above and here, you could actually go and recreate these tones by matching the specific hertz.

Why do some notes sound good together and some don't? When two notes don't sound good together, we call that sound dissonance. There is a scientific explanation for this. When the sound waves cross each other in a pattern at some point in their wave, it produces a sound that is pleasing to the ear. For example, let's take the two notes above of C and G, recorded on my piano.

The combination sounds good to the ear, because the pattern of the sound waves line up every so often in a pattern (for more information that is heavily mathmathical, visit here). Contrast that with the following video, which is of me playing an E and an F.

Ignoring the fact that the video ended up sideways, you should definitely hear a difference. The notes sound extremely dissonant, because the sound waves don't ever cross in any particular pattern, and so clash against each other.

When composers write music, they have to keep these dissonances in mind. In fact, sometimes the best moments in music come when a composer writes a dissonance in on purpose. Here's a an easy example by the Georgia Tech marching band, though I suggest skipping to the 1:30 mark to keep it short and sweet.

I do love the sound of a good, solid marching band. It's interesting you can have so many different instruments and sounds come together like that. Each instrument has its own flavor, or "timbre". (Pronounced "tam-ber". No falling trees here).

In the music world, timbre has nothing to do with volume or pitch. Instead, it refers to the characteristics that make each sound unique. Sometimes timbre is referred to as tone color, but scientifically it refers to the shape of the sound wave. When we think of a normal sound wave, we probably think of the smooth, curved arches we've seen so far. If instead of those arcs, the wave was shaped like a rectangle, the sound would be different.

Go here and play around with some of the different timbres; it's really pretty fascinating!

The more jagged the shape, the more harsh the sound will be. You will find that the smoothest looking sound waves produce the sounds easiest on the ears.

To review, there's a reason why we hear sounds the way we do. Some sounds are pleasing to the ear, and others aren't, depending on how the sound waves match each other. Timbre (or the shape of the sound wave) also greatly affects how we perceive a sound.

So, how good is YOUR hearing? This is fun, but starts out at a hertz only audible to dogs and works its way down. Make sure you're in a quiet environment, and watch your volume if you have headphones in. Pause the video when you hear the sound, and see how you did!

Have you ever wondered what your vocal chords look like? Why is it that sound always carries more over water? We'll dive into that next week on the Science of Sound, Part III!

-DMM