The term 'Nada' is a Sanskrit word which means musical sound, 'Nada' is a combination of 'Nakar' means life or breath and 'Dakar' means fire or energy. When there is a combination of breath and energy 'Nada' or musical sound is produced. In other words, when breath is energised it gives rise to musical sound or 'Nada'. Thus, sound is produced by motion of some kind in the air or any energetic action in the air causes sound.
In fact, sound is a sensation caused by certain oscillatory motions of the particles of a body. Some sounds are melodious and some sounds are harsh and unpleasant to hear. But in every case the source of sound is in a state of vibration. If you closely watch anything which emits sound, you will observe a sort of vibration in it and along with it the sound. If you just pluck the string of a 'Sitar' or a 'Tanpura' ( Musical Instruments) with your finger, it will emit sound. On close observation the string will appear to vibrate. If you again touch the vibrating string with your finger, the vibration will stop and along with it the sound will also cease. Thus, it is clear that vibration is the cause of sound.
These vibrations continue one after the other for some time and stop after a while. When such vibrations are uniform they are called 'Regular Vibrations'. But when such vibrations are flitting , alternately fast and slow, they are called 'Irregular Vibrations'. Then again these vibrations last up to a stated interval of time ad sometimes these vibrations suddenly stop. When these vibrations last for a stated interval of time , they are called 'Non - Periodic vibrations' . Now the sound that is produced by regular and periodic vibrations is called unmusical sound or noise. In other words, a musical sound is produced by regular and continuous vibrations of a body but an unmusical sound or noise is produced by irregular and discontinuous vibrations of a body. Therefore, it can be said that "A musical note is the result of a regular and periodic vibrations of the air particles acting in the air, and therefore also of the body whence they proceed each particle passing through the same phrase at stated intervals of time. On the other hand, the motion to which noise is due is irregular and fitting, alternately fast and slow, and creating in the mind a bewildering and confusing effect of a more or less unpleasant character". 'Encyclopedia Britanica', Vol. I ninth edition. In other words, musical sound is produced by regular and periodic vibrations. It produces continuous and pleasing sensation on the ear. While noise is the result of irregular and non-periodic vibrations. It is a confused mixture of many discordant sounds. It creates in the mind a bewildering and confusing effect of an unpleasant character.
Sound can be divided into two categories :-
(2) Unmusical Sound or noise
Musical Sound or Nada : That sound which is produced by regular and periodic vibrations and which gives a pleasant sensation on the ear is called musical sound or 'Nada'. For example the sound of Sitar, Violin, turning-forks, Sonometer etc.
Unmusical sound or Noise : That sound which is produced by irregular and non-periodic vibrations and which gives an unpleasant sensation on the ear is called Unmusical sound or noise. For example the sound produced by gun shots, or by the hoofs of a running horse.
Since music is concerned with sound, therefore we are interested in that kind of sound alone which is capable of being used in music i.e. musical sound or 'Nada'. Unmusical sound or noise has no bearing with music.
Musical sounds have also been divided into two groups (1) 'Anahata Nada' and (2) 'Ahata Nada'
Anahata Nada : A sound without any earthly cause and which they consider to have existed from all eternity, after the following manner. When a man closes the orifices of his ears with his fingers, he perceives an inwards noise, to which they give this name.
Ahata Nada : A sound which proceeds from a cause which like speech, they consider to be an accident of air, occasioned by percussion
Musical sounds in general exhibit three different qualities, Viz (1) Loudness or Intensity, (2) Pitch and (3) Timbre
NADA :------
(1) INTENSITY
(2) PITCH
(3) TIMBRE
INTENSITY :
Intensity or Loudness of sound is also known as Magnitude of sound. Every body is familiar with the difference between a loud and feeble sound. Intensity of sound depends upon the greater of less energy by which the sound is produced. If the stretched wire of a Sitar is plucked lightly, it will produce less intense sound which will be audible to the persons sitting close by. But, if the same stretched wire is plucked forcibly, the sound will be intensive enough to be heard at a long distance. Again, when a drum is struck violently the sound is louder than when it is struck slowly. Soft and loud sound can also be produced from our throats. If a person pronounces softly the note 'Sa' of the middle octave, it will be audible only to the people sitting close to him. But if he pronounces the same 'Sa' loudly, it will be heard even by the people sitting at a long distance. Thus, intensity or magnitude of sound indicates that the sound which is being produced is soft or loud.
PITCH :
It is the property by which a note of higher pitch is distinguished from that of a lower pitch. If a person pronounces 'Sa Re Ga' these three notes one after the other, it will indicate that the sound of 'Re' is lower than the sound of 'Ga' and the sound of 'Sa' is lower than the sound of 'Re'. Thus a higher note is said to be of high pitch and a lower note is said to be low pitch. The pitch of a sound depends upon the rapidity of vibrations of frequencies of the sound per second. The pitch of a note is higher or lower in proportion to the number of vibrations or frequencies the higher is the pitch of sound;' and the lesser is the number of vibrations or frequencies the lower is the pitch of sound. For example, the frequencies of 'Pa' are greater than the frequencies of 'Sa'. Again, the frequencies of 'Ma' are lesser than the frequencies of 'Pa'. Therefore the pitch of the sound of 'Ma' is lower than the sound of 'Pa'. Hence the pitch of the sound indicates that the sound which is being produced is high or low.
TIMBRE :
Timbre is a French word which means the characteristic quality of sounds produced by each particular voice or instrument. The German word for Timbre is 'KLANGFABRE', KLANG + FABRE. 'Klang' means musical sound and 'Fabre' means colour or quality. Timbre is the property of sound by virtue of which the sounds of different instruments cab be distinguished one from the other or the voice of one man can be recognised from that of another man. The property of timbre enables us to recognise a sound simply by hearing it that it is a human voice. And if so and so is singing. Similarly when an instrument is played, we can say simply by hearing its sound as to what particular instrument is being played. It is by virtue of this property of sound that a blind man is able to recognise the sounds of different instruments or the voices of different persons simply by hearing their sounds or voices. Thus timbre indicates that the sound which is being produced is a human voice or belongs to some instrument such as 'Voilin, Sitar or Tabla.
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