The works of Ādi Śaṅkarācārya

Taittirīyopaniṣadbhāṣyam

Verse 2

शीक्षा व्याख्यास्याम ।वर्णः स्व-रः ।मात्रा बलम् ।साम सन्तानः ।इत्यु-क्तः शीक्षाध्याय ॥ १ ॥

In plain words

We shall now expound the science of phonetics: individual sounds, pitch accents, duration of pronunciation, strength of articulation, evenness of tone, and the continuity of recitation. Thus is declared the chapter on phonetics.

Close to the Sanskrit

Phonetics we shall expound. Sound, accent, quantity, strength, evenness, and continuity. Thus is declared the chapter on phonetics.