Appendix
Chapter6 The Three Elements of Sound
Sounds are waves that vibrate through the air. These waves eventually reach our ears, and we would recognize them as sounds. The shape of the wave determines its sound.
Harmonics
In concept, sounds are composed of three elements: pitch, volume, and brightness.
Pitch
We’ve just talked about the brightness of sounds, and how they are determined by the shape of their waveforms.
But how are these waveforms constructed? It is commonly known that waveforms are composed
of a combination of sine waves.
Sawtooth Wave |
| Square Wave |
|
|
|
The pitch of sound is determined by the speed of the wave cycles. A wave that vibrates 1 cycle per second is called
1 Hz (hertz). As the frequencies become higher, Hz becomes higher in numbers. Lower the number in hertz, and frequencies will become lower as well. For example, when A4 (center A) equals 440.0 Hz, an octave higher pitch would generate twice the amount of frequency
at 880.0 Hz (A5). An octave lower pitch would produce half the frequency at 220.0 Hz (A3).
1Hz sound wave
time
1sec
A5 (=880Hz) 
time
A4 (=440Hz) 
time
A3 (=220Hz) 
time
Let’s take the sawtooth or the square wave for example; they are comprised of a sound basis and additional sine waves that are the integer multiples as in two times or three times
the frequency (called harmonics, or overtones). There are two kinds
of harmonics. One has the frequencies
of integer multiples in two times or three times; the other has other frequencies that are
By combining these harmonics, various sounds can be created.
time |
|
|
|
| time |
|
|
|
| ||
|
|
|
|
|
|
3rdpartial 2ndpartial fundamental | 5thpartial 4thpartial | 6thpartial | partials | 5thpartial 4thpartial 3rdpartial 2ndpartial fundamental | 7thpartial 6thpartial | partials |
|
|
|
|
|
Brightness
Bright waveform
The brightness of a sound is determined
by the shape of its waveform. By comparing the piano and the square wave side by side, you can see the difference in complexity.
In this example, the complexity of the waveform results in a brighter sound.
Piano waveform (complex) | Sine waveform (smooth) |
“clang” | “poooh” |
time | time |
Brighter sounds include many high frequency harmonics; darker (rounder) include more of the low frequency harmonics. There is a technique called subtractive synthesis method in which harmonic elements are cut to change the brightness (waveform) of the sound. It is a popular method for creating composite waveforms. The
time
Low pass filter
level | partials which are cut |
| |
| frequency |
Volume
The volume of the sound is determined by the size or the width of the waves. As the waves become
wider (vertically on the graph), the louder | time | time |
|
| |
the volume becomes. As the width narrows, | Loud sound | Soft sound |
| ||
the volume becomes softer. |
| |
|
|
to change the brightness of the sound.
Higher partials are cut, making
the waveform more rounded (mellow)
time
Chapter
6
Appendix
Elements of | The Three |
Sound |
|
23 | 24 |