Structure
Vibration in nature
A sine wave sound cannot be found in nature, because that would require an absolutely undistorted sound source and environment. Thus, all natural vibrations are complex.
While a column of air or a vibrating solid will initially vibrate with a simple vibration, within a few milliseconds it will begin to form additional types of vibration. First vibrating along its whole length, it will then vibrate in halves, then in thirds, fourths etc.
This vibration, with frequencies consisting of integer multiples of the basic vibration, is called harmonic vibration.
If the vibration components are not integer multiples, the vibration is called non-harmonic vibration. With such a sound, pitch is usually difficult to determine.
A completely irregular vibration produces noise; an example would be the sound of wind in the trees.
While a column of air or a vibrating solid will initially vibrate with a simple vibration, within a few milliseconds it will begin to form additional types of vibration. First vibrating along its whole length, it will then vibrate in halves, then in thirds, fourths etc.
This vibration, with frequencies consisting of integer multiples of the basic vibration, is called harmonic vibration.
If the vibration components are not integer multiples, the vibration is called non-harmonic vibration. With such a sound, pitch is usually difficult to determine.
A completely irregular vibration produces noise; an example would be the sound of wind in the trees.
In music, to produce an identifiable pitch, instruments must produce clear wave forms (close to harmonic vibrations), with an easily definable frequency and timbre.
Here are some wave forms produced by musical instruments. T equals one wavelength, or one period, or oscillation.
Here are some wave forms produced by musical instruments. T equals one wavelength, or one period, or oscillation.
The wave form of a sound can be analysed into its constituent parts by using Fourier analysis. The result is an image showing the partials and their amplitudes. This graphic representation of a sound is known as a spectrum.
This image shows the spectrum of a synthetic sawtooth wave. It shows that the partials are harmonic (i.e. integer multiples of the fundamental frequency) and that the amplitude of each partial is in inverse proportion to its integer coefficient (e.g. the 5th partial is 1/5 of the amplitude of the fundamental).
Voimakkuus = amplitude
Osaääneksiä = partials
This image shows the spectrum of a synthetic sawtooth wave. It shows that the partials are harmonic (i.e. integer multiples of the fundamental frequency) and that the amplitude of each partial is in inverse proportion to its integer coefficient (e.g. the 5th partial is 1/5 of the amplitude of the fundamental).
Voimakkuus = amplitude
Osaääneksiä = partials
Below is an example of how a pulse wave is built by adding harmonic partials. In pulse wave form all partials have the same amplitude.
The adjacent image shows the spectra of certain sounds.
A pure sine tone only contains one partial – itself.
White noise (like white light) contains all possible frequencies at the same amplitude.
The spectrum of a violin sound shows that the partials are of different strengths. The string it self has it's own partial structure and it is connected to the body of the violin, whose resonance changes the overtone profile of the sound of the string.
Siniäänes = sine partial
Valkoinen kohina = white noise
Viulun sävel = a tone of a violin
Taajuus (Hz) = frequency (Hz)
Voimakkuus = amplitude
A pure sine tone only contains one partial – itself.
White noise (like white light) contains all possible frequencies at the same amplitude.
The spectrum of a violin sound shows that the partials are of different strengths. The string it self has it's own partial structure and it is connected to the body of the violin, whose resonance changes the overtone profile of the sound of the string.
Siniäänes = sine partial
Valkoinen kohina = white noise
Viulun sävel = a tone of a violin
Taajuus (Hz) = frequency (Hz)
Voimakkuus = amplitude
This link is to a synthesiser where you can experiment with varying the relative amplitudes of partials to see the wave forms they generate.
This website will open in a new window.
Additive synthesis website
This website will open in a new window.
Additive synthesis website
Facts:
- A sonorous sound can be analysed into sine waves
- A harmonious sound consists of a fundamental frequency and its integer multiples
- In a non-harmonious sound, not all of the partials are integer multiples of the fundamental
- Noise contains all possible sine waves
- The structure of a sound at a given moment is illustrated with a spectrum, showing the frequencies and amplitudes of the partials
version 29.6.2022