Ba is the voiced labial stop and the third letter of the labial class, differing from the head of the class by voicing alone. It carries the inherent short a, takes the full range of vowel marks, and enters conjuncts in the ordinary way.
Its distinguishing problem is not phonetic but graphic. In many Indic manuscript hands the letters for this sound and for the labial semivowel are drawn so alike that scribes confuse them, and the two sounds fell together in several of the languages written with these scripts, so the confusion entered by the ear as well as by the eye. Siddham shares the difficulty in full.
The consequence for anyone editing a text preserved in the script is that a manuscript reading of one letter is often an editorial decision about the other. Where a word is known from elsewhere the decision is easy; where it is a name, a technical term or a syllable from a dharani, it may not be recoverable at all, and a responsible edition marks the uncertainty rather than choosing silently.
The letter itself is unremarkable in the vocabulary, less frequent than most of the labial class, and its position in the table is fixed by voicing in the same way as the voiced stop in each of the other four classes.