1. A method comprising: presenting a plurality of human-testers with obtained speech utterances; receiving, for each presented speech utterance, one or more human-tester generated speech utterances being human repetitions of the presented speech utterance; generating an utterance-specific scoring model for each one of a plurality of the obtained speech utterances, based on respective human-tester generated speech utterances, each scoring model being usable to estimate a level of speech naturalness for a respective one of the obtained speech utterances; and obtaining a speech naturalness score for each presented speech utterance by respectively applying the utterance-specific scoring model to each presented speech utterance, wherein at least one of: the presenting, the receiving, the generating, and the obtaining is performed by at least one computer.