The TIMIT corpus
A joint effort by MIT, SRI and Texas Instruments produced a corpus of 630 speakers across eight dialects, annotated at the phoneme level.
Why it matters
Speech recognition got a shared ruler five years before text processing got the Penn Treebank.
Each speaker read ten phonetically rich sentences: 6300 sentences in all, more than five hours of speech with time-aligned transcription. The recording was done at Texas Instruments, transcription at MIT, verification and publication by NIST. The corpus is still used as a teaching example, though its size is long since trivial. What it established matters more: results became comparable between laboratories.