Voiceprints, like fingerprints, may be unique and almost unchangeable

In tests, voiceprints had been made of the same word spoken by different persons, each person uttering it several different times. Each utterance of the word was voice-printed on a separate card. Then the cards were shuffled, and trained subjects were asked to group the cards representing each voice. Out of about 25,-000 decisions, these trained people made the right decisions more than 97 per cent of the time.