Most speech corpora contain read speech, either for practical reasons because eliciting non-read speech is more difficult or simply because the intended application or investigation requires read speech. Read speech can be recorded by using so called prompt sheets or by displaying text on a graphical output device.
Dictation speech is a special case of read speech: the speakers are asked to read a text as in a dictation task. Exact instructions must be specified how special cases like acronyms and numbers have to be spelled consistently.