Helping the law make a sound case
Deciphering the words of an urban rapper was probably the last way Martin Barry ever thought he would earn his living when he studied languages at Cambridge.
But his expertise helped convict the man, who was accused of plotting to kill a pregnant woman.
"It was one of my punch-the-air moments," said the former head of linguistics at the University of Manchester, who has been a full-time forensic voice expert for the past three years.
The case involved the rapper claiming he was recording a track in a studio when an attempt was made to murder the girlfriend of his friend and fellow rapper.
Mr Barry, 49, had to help prove whether there was a genuine date and time stamp on a recording by Kingsley Ogundele, known as rapper Snoopy Montana.
If the date was authentic, Ogundele had an alibi.
However, when he checked another recording with an earlier time stamp he found the two were identical.
This cast grave doubt on Ogundele's alibi because of the possibility his recording was merely a copy of an earlier rap.
It was Mr Barry's skill as a "voice detective" which helped him deliver his evidence.
But can confirming two recordings are identical be that difficult? Surely anyone listening could decide if they were the same?
Mr Barry said forensic voice experts subjected speech samples to careful listening, making a phonetic analysis of patterns of speech.
He also explained people's memories of voices were notoriously unreliable.
Mr Barry cited how one academic could not even recognise the voice of his own mother in a short recorded clip.
"People think it is easier to recognise familiar voices but that is because when you are speaking to your mother on the phone you are not expecting to hear anyone else."
But according to Mr Barry, the kind of evidence he and others in his field produce is unlikely to ever gain a conviction or acquittal on its own.
"People look for the 'CSI effect' where you hear them saying: 'That's the guy' - it doesn't work like that.
"It's not like DNA evidence, where you can have a sample which is a close match to a suspect.
"The human voice is very flexible."
Sometimes he is called on to help decipher words from the smallest scraps of acoustic evidence on crackling tapes.
Mr Barry explained that with degraded recordings, speech experts were piecing together fragments of sounds, vowels and consonants, like an archaeologist uncovering a wall inscription.
Analysing recorded evidence is a relatively new form of criminal inquiry with the first high profile instance being the infamous "I'm Jack" tapes sent to West Yorkshire Police during the Yorkshire Ripper investigations in the late 1970s.
The voice experts called on by police pinpointed the man's accent to a district of Sunderland.
'It was a hoax'
"They also told police they felt sure it was a hoax - even though this was not their field - and were ignored and more women were killed," said Mr Barry.
He explained while there were automatic computer-based systems for identifying voices these were not good enough for forensic purposes.
Surprisingly, in the digital era, many police forces still rely on cassette tapes, with their attendant background noise and poorer sound quality, for recording interviews.
The Association of Chief Police Officers recommended the switch to digital three years ago citing the difficulty in getting spare parts for analogue machines and criticisms from judges about the quality of recordings.