An overview of the Lincoln Laboratory speech recognition system

The Lincoln speech recognition system is capable of recognizing spoken sentences made up of words drawn from a limited vocabulary and constrained to conform to a context‐free grammar. Speech input is taken from a close‐talking, noise‐cancelling microphone in a relatively noisy computer room. The speech is digitized and subjected to a detailed acoustic‐phonetic analysis [C. J. Weinstein et al., Proc. IEEE Symposium on Speech Recognition (April 1974), pp. 89–100] which produces a string of acoustic phonetic elements (APELs). The APEL string is scanned by a linguistic module which attempts to find and score candidate sentences which satisfy the syntactic and semantic constraints of the grammar and which are composed of words having acceptable matches between phonemic dictionary spellings and APEL representations. Typical sentences of 3‐ to 4‐sec duration require the order of one minute of computer processing. Tests have involved vocabularies of 125 to 500 words, grammar of varying complexity, many speakers (both male and female), and several hundred test sentences. [This work was sponsored by the Advanced Research Projects Agency of the Department of Defense.]