1. A computer-implemented method of generating speech including audible breath sounds, the method comprising: receiving input text for text-to-speech (TTS) processing; identifying punctuation in the input text; determining a first location in the input text for insertion of a breath sound based at least in part on the punctuation; determining a second location in the input text for insertion of a breath sound based at least in part on the punctuation; determining a linguistic distance between the first location and second location; using a cost function to identify a first breath unit for the first location, the cost function based at least in part on the identified punctuation, the linguistic distance between the first location and second location, and a linguistic context of the first location; using the cost function to identify a second breath unit for the second location, the cost function based at least in part on the identified punctuation, the linguistic distance between the first location and second location, and a linguistic context of the second location; and synthesizing speech corresponding to the input text, wherein the synthesized speech comprises a first breath sound corresponding to the first breath unit at the first location and a second breath sound corresponding to the second breath unit at the second location.
3. The computer-implemented method of claim 1 , further comprising determining a rate of speech based at least in part on a duration of the first breath sound, and wherein synthesizing the speech is based at least in part on the determined rate of speech.