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Listener method


In the listener method, the decision of similarity is taken by human experts after audition of speech samples. One of the methods is the repeated listening of the available samples by a group of experts looking for similarities in linguistic, phonetic and acoustic features. The voices listening test can be done either sequentially or alternatively or finally, by simultaneous presentation of the voices, if allowed by the instrumentation. The acoustic material is carefully prepared, selecting from the database suitable utterances of the unknown and of the reference speaker, eventually augmented with voice samples coming from speakers with the same acoustic-phonetic characteristics. These utterances are then compared two by two, inverting pairs of voices from the same speaker. Studies have been carried out to investigate how well listeners can recognise speakers [Stevens et al. (1968)]. Listener performance is a function of acoustic variables such as the signal-to-noise ratio , the speech bandwidth , the amount of speech material, complex distortions  of the speech signal introduced by speech coding transmission systems, etc. Several experiments using different texts for comparing and evaluating the performance under different degraded conditions showed that human listeners are robust speaker recognisers  when presented with degraded speech. This is due to the fact that there are many sources of knowledge that contribute in various ways to speaker recognition , providing weak, moderate or high discrimination power. However, as with any human decision process, it must be stressed that the listener method leads to a subjective decision. Nevertheless, the listener method is still used in some countries for forensic applications as a technique for speaker recognition .

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