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What are Fundamental Tone and Overtones?
Musical sound: The sound produced due to regular and periodic vibrations, that is pleasing to hear, is called musical sound. While singing, the vocal chords of a singer vibrate with regular periodic motion. Similarly when the strings of a sitar are excited to produce a certain note, they vibrate with regular periodic motion. The sound of clapping is usually unpleasant, but rhythmic clapping of hands may produce a pleasant sound. This is due to the regular vibration of the source. Similarly patter of raindrops on tin roofs or the clickety sound of train wheels may be sonorous.
Noise: The sound produced by an irregular or short lived vibration is called noise. The explosion of a cracker, firing of a gun, horn of a car, etc., are noises.
Tone: Musical sound of a single frequency is called a tone. When the source of sound vibrates in SHM, it produces a tone. The two prongs of a tuning fork vibrate in SHM and produce the sound of a single frequency. Thus, the sound of a tuning fork is a pure tone.
Note: Musical sound due to a mixture of more than one frequencies is called a note. The sound produced by different musical instruments consists, in general, of more than one tones. If a tone is compared with monochromatic light such as red light, a note can be compared with compound light, i.e., white light.
The tones within a note are classified on the basis of their frequencies.
Fundamental tone: The tone with the lowest frequency present in a note is called the fundamental tone.
Overtones: The tones in a note, other than the fundamental tone, are called overtones.
Harmonics: Harmonics are tones having frequencies that are integral multiples of that of the fundamental tone. The fundamental tone is also a harmonic.
Octave: A tone whose frequency is twice that of the fundamental tone is said to be the octave of the fundamental tone.
Suppose, a musical note consists of tones of frequencies 200 Hz, 300 Hz, 400 Hz, 500 Hz and 600 Hz. So it can be said:
i) Each of these live different frequencies corresponds to a tone,
ii) The combination of these five tones is a note,
iii) The tone of 200 Hz is the fundamental tone,
iv) The tones having frequencies 300 Hz, 400 Hz, 500 Hz, 600 Hz are overtones,
v) Both of the two tones of frequencies 400 Hz and 600 Hz are harmonics, as the frequencies are 2 and 3 times that of the fundamental tone respectively. The tone of 400 Hz is called the second harmonic as its frequency is 2 times that of the fundamental tone, Similarly, the tone of 600 Hz is called the third harmonic. The fundamental tone is called the first harmonic.
vi) The tone of 400 Hz is the octave because this frequency is twice the frequency of the fundamental tone.
Characteristics of musical sound or note: There are three characteristics which differentiate musical notes. These are loudness, pitch and quality.
- Loudness: Loudness is related to the sound energy reaching our ears per unit time. If the sound energy reaching our ears in I second goes up, we perceive a corresponding increase in the loudness.
- Pitch: It is that characteristic which differentiates a sharp or a shrill sound from a grave one. It increases with the increase in frequency of the source.
- Quality or timbre: It is that characteristic of a musical note which enables us to distinguish between a note emitted by one musical instrument from a note of the same loudness and pitch emitted by another instrument. It depends on the number of overtones present in a note and their relation with the fundamental tone.