AFAIK current ASR systems uses grapheme transcriptions for training their acoustic models. So they have the speech and the transcription "Hello World" and durin

AFAIK current ASR systems uses grapheme transcriptions for training their acoustic models. So they have the speech and the transcription "Hello World" and during training, they are automatically converted to phones kind of "hələʊ wɜ:ld" using extensive phonetic dictionaries and some algorithms. 9287 is context dependent phones. like "a" but there is a "b" on the left and "r" on the right. Theoretically for 40 phones you end up 40^3 context dependent phones. But in practice this number is much lower.