The Śākala tradition is mainly followed in Maharashtra, Karnataka, Kerala, Odisha, Tamil Nadu and Uttar Pradesh.
The Mahābhāṣya of Patañjali refers to 21 śākhās of the Rigveda; however, according to Śaunaka's Caraṇa-vyuha there are five śākhās for the Rigveda: the Śākala, Bāṣkala, Aśvalayana, Śaṅkhāyana, and Māṇḍukāyana, of which only the Śākala and Bāṣkala and very few of the Aśvalayana are now extent.
[1] As far as the Rigveda is concerned only Śākala Śākhā is preserved out of 21 which existed at one time.
There is a claim that Śaṅkhāyana Śākhā is still known to a few Vedapathis in Uttar Pradesh and Gujarat but this is not certain.
[3][1][4][1][5][6] Śikṣā as a term for phonetics, is first used in Taittirīya Upaniṣad, which gives its various components which include Varna (individual sounds) and Svara (accent).