The generation of synthetic speech signals in order to convey information to listeners, usually based upon a verbal or textual request by the users. This speech synthesis typically employs a computer program and requires access to storage of portions of speech previously spoken by humans. The naturalness of the synthetic voice depends on several factors, including the vocabulary of words to pronounce, the amount of stored speech, and the complexity of the synthesis programs. The most basic voice response simply plays back appropriate short verbal responses, which are only copies of human speech signals stored using digital sampling technology. The most universal systems, on the other hand, are capable of transforming any given text into comprehensible speech for a given language. These latter systems so far exist for only 20 or so of the world's major languages, and are flawed in producing speech that, while usually intelligible, sounds unnatural.