The Physics of Sound

Not all musicians like to get into the science or physics of sound, just like not all students of physics are not interested in music! Here is some basic information for the exceptions who might be interested in both!


  1. Sound is a form of energy generated from objects, propagated through a medium.
  2. Frequencies that can be heard by living beings are called “Dhwani” in Sanskrit.
  3. Sounds are of two kinds:
    1. Musical (“naad“) and
    2. Non-musical (noise or “kolaahal“).


  1. Naad is a Dhwani that has relatively consistent sound properties i.e. it has consistency of frequency, amplitude and timbre. Naad, literally, is the sound of music.
  2. The commonest example of ‘Naad‘ is a musical sound made on a stretched string under constant tension.
  3. It is thus ‘musical sound’ or ‘sangitik dhwani’ as it is pleasing to the human ear.
  4. There are two kinds of Naad:
    • Ahat Naad – any musical sound that emanates from the striking of two objects.
    • Anahat Naad – is more of an abstract musical sound. It is said to be the sound of the cosmos which can be attained through meditation.
  5. Saptak is a range of musical sound frequencies and thus there are infinite naads in the saptak.


  1. To create music, we need to ‘dwell’ on certain naads. Musicologists, with the help of natural consonant laws and mathematical calculations have identified 22 Naads to define music – called shrutis.
  2. So, from Ahat Naad, which is millions of nano-tones, we got 22 distinguishable micro tones used in Indian Music known as Shrutis, which range from 261.63 Hz to 496.69 Hz in frequency.


  1. From these came twelve Svaras or notes in an octave out of which seven were shudhh/pure notes and five were vikrit i.e. slightly lower or higher than some of the pure notes.
  2. Each raag or melodic composition requires certain kinds of shrutis in order to set a specific mood (as the correct mood in Indian Classical music performance is achieved only with proper pitching which comes with the proper use of shrutis).
  3. The chosen shrutis thus become the representatives of the svaras of that raag.
  4. So every svar is a shruti, and every shruti is a naad, every naad is a dhwani but the vice versa is not true. 
  5. Carnatic Music uses the Shrutis in a more pronounced way. Hence, it uses more svaras.
  6. More about Svaras, Shrutis & Saptak here: The Science of Music

What turns some Sounds into Music?

  1. All music is sound, but not all sound is music. In fact, most sound is not music; it is noise
  2. Music was one of the earliest forms of nonverbal auditory communication between the producer and the receiver.
  3. Music is different from other forms of auditory communication, like speech in being more universal and evoking emotion. It is also relative and subjective. What is music to one person may be noise to another.
  4. All music is based upon and conditioned by relations between sounds, and all pleasant sounds do not qualify as music. For example, the ringing of a bell is not unpleasant, but it is not music. Whistling is a pleasant enough sound, but not music – unless the pressure of the breath is varied and the sound then might start approaching the quality of music. So it is not just sound but variations in sound that go into the making of music.
  5. We can identify the difference between two constant sounds e.g. between the constant ring of a bell and the constant hum of our whistling. We can also recognize the difference between the rings of two different types of bells.
  6. But the volume alone is not sufficient to distinguish between constant sounds. e.g. we can tell apart two persons on the phone, even if they be of the same age and sex. It is easy if age-difference is big e.g.a 21-year-old and a 3-year-old, even if both males; gender is even easier. but still, there is something distinct about every sound – and that is Pitch!
  7. Pitch makes us sound gruff or shrill or low and high or flat and sharp.
  8. Therefore, there are two key attributes of sound:
    • The first defines the volume of sound on the spectrum between soft and loud.
    • The 2nd helps us identify the difference between sounds – Pitch!

  1. Read More about Pitch, Svaras, Shrutis & Saptak here: The Science of Music.
  2. Read More about How Sound Waves Work.
  3. Many concepts in this write-up have been excerpted or reproduced from a series of very informative & educative articles by Anjum Altaf. You can read the original here: An Idiot’s Guide to Music.]

More on Indian Classical Music:
The Alchemy of Indian Classical Music

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