7. An apparatus comprising: at least one processor programmed to perform: providing a first prompt to obtain a text-dependent audio sample from a user at an evaluation stage; providing a second prompt to obtain a text-independent audio sample from the user at the evaluation stage; and making an authentication decision about the user based, at least in part, on results of: a comparison between characteristics of the text-dependent audio sample and an enrollment audio sample received at an enrollment stage and a comparison between characteristics of the text-dependent audio sample and the text-independent audio sample.
7. An apparatus comprising: at least one processor programmed to perform: providing a first prompt to obtain a text-dependent audio sample from a user at an evaluation stage; providing a second prompt to obtain a text-independent audio sample from the user at the evaluation stage; and making an authentication decision about the user based, at least in part, on results of: a comparison between characteristics of the text-dependent audio sample and an enrollment audio sample received at an enrollment stage and a comparison between characteristics of the text-dependent audio sample and the text-independent audio sample. 8. The apparatus of claim 7 , wherein the at least one processor is programmed to generate an utterance validation score based, at least in part, on the text-independent audio sample received at the evaluation stage.