Most objects vibrate in a more complex way than a simple back and forth motion. The more complex the vibrations, the more complex the resulting soundwaves.
Simple soundwaves can be added together. When this happens, more complex and interesting soundwave patterns appear.
Any sounds can be added together, and characteristics of the initial sounds will often be transferred into the final complex sound. As explored in Generating Sounds, the three general categories of sound are noise, impulse click and pitch sounds. Pitched sounds are regular, while noise sounds are erratic and impulses are very short. These three sound types can be thought of as extreme types of generated sound. Many other sounds exist between these extreme points as a mixture of all three sound types. Mixing between these three extremes will give us an unlimited supply of hybrid and complex sounds.
We can see the difference between noisy and pitched sounds by creating a sonogram for each type and comparing them.
Image of a Noise Sound
Image of a Pitched Sound
As sounds get more complex, so do their visualisations.
Combining Wave Types
A Hybrid Sound
Can you hear the difference and similarities between the original sounds (above) and the final output sound?
Beyond Basic Sound Types
Objects that vibrate in a more ordered fashion produce sounds that we describe as pitched. This is because the sounds produced contain a greater focus of soundwave energy, with frequencies concentrated into narrow bands. These concentrations of soundwave energy are called partials.
Partials of the Guitar
Here you can see the many partials (horizontal lines) which make up the guitar sound. The guitar string itself is very narrow, and this narrow size causes the vibrational energy to remain very focused. When the string vibrates, it can only do so in a number of ways. The image below shows some of the various rates of vibrations which occur as the string is plucked. Each of these different waves of vibration relate to partials that you can see in the sonogram of the guitar sound (above).
The Combined Waveform
All of the vibrations occur simultaneously as the string is struck, and they interact with one another to create a complex waveform pattern. The relationship of partials within a pitched sound can also affect the type of sound that we hear.
If the partials making a sound are related to one another by whole number ratios, we can describe the sound as harmonic.
The guitar sound is an example of a harmonic sound.
You can see in the sonogram (above) that all of the partials are evenly and regularly spaced.
Where the partials are not evenly spaced, we describe the sound as inharmonic.