https://www.bilibili.com/video/BV1hZ4y1w7j1?p=2&vd_source=4aed82e35f26bb600bc5b46e65e25c22
phoneme: phonetic symbols, the basic unit of pronunciation, lexicon: vocabulary, Grapheme: the basic unit of writing, 26 letters
The blue box is rnn, 
The smallest pronunciation unit, its distribution is fixed, and the pronunciation is fixed
It is equivalent to using deeplearning to generate word2vec without mfcc
align is the relationship between mfcc and ab, the sum of all possible probabilities.
Exhaustively enumerate all possibilities in the following way, and sum them up to align.
