Overtones, also known as harmonics, are higher frequency sound waves that occur simultaneously with the fundamental frequency (the main note) when an object vibrates, contributing to the unique timbre or tone color of a sound. While they are naturally present to varying degrees in most musical sounds, they can also be produced intentionally using specific techniques.
Producing Overtones on String Instruments
For string players, a common method to produce clear, isolated overtones is by lightly touching the string at specific points while plucking or bowing. This technique creates what are sometimes called "ghostly sounding notes".
The Science Behind String Harmonics
When a string vibrates normally, the entire string oscillates at its fundamental frequency, but also vibrates in smaller segments simultaneously. These smaller segmented vibrations correspond to the overtones.
By gently touching the string at certain points, you prevent the string from vibrating fully at the fundamental frequency at that specific location, forcing that point to be a node (a point of minimum vibration). This allows the string to vibrate more strongly in the segments defined by the touch point and the fixed ends.
Here's how specific touch points relate to harmonics, as described in the reference:
- Touching the string lightly at the middle (halfway along its length) forces a node at the midpoint. This encourages the string to vibrate in two halves, producing the second harmonic (an octave above the fundamental).
- Touching lightly at one-third the string length (for example, often found near the 7th fret on a guitar) forces a node at that point. This encourages the string to vibrate in three segments, producing the third harmonic (an octave and a perfect fifth above the fundamental).
- Touching lightly at one-fourth the string length (e.g., near the 5th fret on a guitar) forces a node, causing the string to vibrate in four segments, producing the fourth harmonic (two octaves above the fundamental).
And so on – touching at 1/N the string length tends to isolate the Nth harmonic.
| Touch Point Location | Segments of Vibration | Harmonic Produced | Interval Above Fundamental |
|---|---|---|---|
| Middle (1/2) | 2 | Second (2nd) | Octave |
| 1/3 Length | 3 | Third (3rd) | Octave + Perfect Fifth |
| 1/4 Length | 4 | Fourth (4th) | Two Octaves |
| 1/5 Length | 5 | Fifth (5th) | Two Octaves + Major Third |
Why They Sound "Ghostly"
Overtones produced this way often sound pure and clear because you are isolating specific, simpler modes of vibration compared to the complex mix present in a standard note. They lack the richness and full spectrum of harmonics found in a fundamental note played with the entire string vibrating freely.
While this technique is particularly evident on string instruments, overtones are also produced in other ways:
- Wind Instruments: Overtones are produced by changing lip pressure (brass) or airflow and fingerings/valves, causing the air column to vibrate in segments.
- Voice: The vocal cords vibrate, creating a fundamental pitch, and the shape of the vocal tract (mouth, throat, nasal cavity) filters and emphasizes certain overtones.
- Percussion: The material and shape of a drumhead, cymbal, or bar determine which overtones are produced and how they decay.
In summary, overtones are higher frequencies present in a sound, and on string instruments, they can be intentionally produced by strategically touching the string to isolate specific modes of vibration, resulting in clear, often "ghostly" notes.
