Basic Acoustics, Swara and Shruti, Technical Terminology
What the domain covers
This is the theory-of-sound section: pitch, loudness, timbre, resonance, the 22 shrutis, and the technical vocabulary of Hindustani music. Expect one-line definitions and a small numerical question.
Core rules and concepts
- Sound is a vibration travelling as a wave. Frequency (Hz) fixes pitch; amplitude fixes loudness (decibel); the harmonic spectrum fixes timbre - that is why a sitar and a sarod on the same Sa sound different.
- A string's frequency depends on length, tension and mass per unit length: shorter, tighter, thinner strings sound higher. This is why frets shorten the sounding length and why pegs tune.
- Resonance explains the tumba and the tarab; overtones shape the jawari buzz.
- The saptak has 12 swaras (Sa, re, Re, ga, Ga, Ma, M̑, Pa, dha, Dha, ni, Ni). Shruti is the smallest theoretical interval; Bharata's Natyashastra gives 22 shrutis, and different traditions allot them differently among the swaras.
- Just-intonation ratios: Sa 1:1, Re 9:8, Ga 5:4, Ma 4:3, Pa 3:2, Dha 5:3, Ni 15:8. Equal temperament makes each semitone 100 cents.
Worked example
Take Sa = 240 Hz. Pa is the 3:2 ratio, so 240 × 3/2 = 360 Hz, which is 702 cents above Sa. In equal temperament Pa = 240 × 2^(7/12) ≈ 359.7 Hz. The 0.3 Hz difference is why trained ears hear just-intonation Pa as brighter than tempered Pa, and why tanpura tuning is done by ear.
Traps that cost marks
Treating shruti and swara as synonyms; saying there are 22 keys (shruti is an interval, not a note); confusing loudness with pitch; writing 'frequency' where timbre is meant. In terminology questions, define in one sentence - meend, kan, gamak, murki, jhala, toda - without examples.