Taittirīyopaniṣat 01.02
ॐ शिक्षां व्याख्यास्यामः। वर्णस्वरः। मात्रा बलम्। साम सन्तानः। इत्युक्तः शीक्षाध्यायः ॥२॥
Oṃ. We shall explain phonetics: letters and sounds, measure, strength, intonation, and continuity. Thus is the chapter on phonetics stated.
Taittirīyopaniṣat 01.02
वरणीयो वर्णः। स्वरतेस्तु स्वरः। मानात् त्राता मात्रा। बलरूपः। समश्च सर्वरूपेषु। सन्ततश्च।
As he is the desirable object (varaṇīyaḥ), he is 'varṇaḥ', the letter depicting the sound. As he is the one who takes delight in himself (svarateḥ), he is called 'svaraḥ', the vowel sound.
The unit of measure is the protector. It has the form of strength. It is equal in all forms and is continuous.
वर्णादिवाचकं रूपं ज्नेयं वरणादिनामकम्। विष्णोर्वर्णादिसंस्थं च पुंसु तत्तत्क्रियाप्रदम्॥
The form that denotes varṇa and similar categories should be understood as named beginning with varaṇa. That which is established in Viṣṇu, beginning with varṇa, and in a person, grants each corresponding action.