1. A method for use with a speech-enabled application, the method comprising: receiving, from the speech-enabled application, input comprising a plurality of text strings; identifying a first portion of a first text string of the plurality of text strings that differs from a corresponding first portion of a second text string of the plurality of text strings, and a second portion of the first text string that does not differ from a corresponding second portion of the second text string; assigning contrastive stress to the identified first portion of the first text string, but not to the identified second portion of the first text string; generating, using at least one computer system, speech synthesis output corresponding to the plurality of text strings, the speech synthesis output identifying a plurality of audio recordings to render the plurality of text strings as speech, at least one of the plurality of audio recordings being selected to render the first portion of the first text string as speech carrying contrastive stress, to contrast with the rendering of the second text string; and providing the speech synthesis output for the speech-enabled application.