A diphone brackets exactly one phoneme-to-phoneme transition. Diphone boundaries are usually positioned near the midpoint of the most stationary (non-changing) region of two consecutive phonemes. Theoretically, a phoneme inventory of 50 could give rise to up to 2,500 diphones, but not all diphones exist in a given language. For general American English, a minimum of about 1,500 diphones are necessary.

 Voice Sample Synthesis