Phoneme, Grapheme, Lexicon & Design Choices for ASR

Definitions:

Phoneme – Distinct sounds in a language

Grapheme – Distinct unit written in a language

Lexicon – Dictionary that maps phoneme to graph(i.e. Arpabet)

Architecture design choices of the above for ASR :

1. Target audio straight to Grapheme(without lexicon) – so basically extract features to Graphemes(words) – used in small datasets.

2. Go through intermediate step from audio to phoneme to grapheme (less comparisons).