Most acoustic models used by ‘Open Source’ speech recognition (or Speech-to-Text) engines are ‘Closed Source’. They do not give you access to the speech audio and transcriptions (i.e. the speech corpus) used to create the acoustic model.

The reason for this is that Free and Open Source (‘FOSS’) projects are required to purchase large speech corpora with restrictive licensing. Although there are a few instances of small FOSS speech corpora that could be used to create acoustic models, the vast majority of corpora (especially large corpora best suited to building good acoustic models) must be purchased under restrictive licenses.