Taped conversations, such as the controversial recording of disgraced former cricket captain Hansie Cronje's alleged match-rigging, can be used as scientific evidence if properly examined.
Superintendent Jacques Grobbelaar, a forensic analyst from the South African Police Service forensic science laboratory's electronics component, said verifying the authenticity of recorded conversations and identifying specific speakers could be done by experts in this field.
Grobbelaar said it was possible to determine whether a tape had been edited or tampered with by analysing the recording with the aid of a computer.
He said the taped conversation would be listened to in full, and the sound waves placed on computer.
"When a person presses the record button, it leaves a unique magnetic impulse on the tape. The conversation is recorded and when the stop button is pressed it leaves another magnetic impulse.
"We look at these impulses and, if you run through the entire tape and find no unexplained impulses, you can generally say it is an authentic recording," said Grobbelaar.
He said the impulses were not always audible, and were always transferred from tape to tape if an edited tape was re-recorded. A study of a recording would, therefore, be considered an accurate evaluation if conducted by a qualified expert.
Voice authentication was another scientifically based analysis, mainly done on computer and involving a visual analysis of data.
Grobbelaar said the voice recording would be taken down on a spectrograph, which is a computerised graph showing the combination of sound frequency and energy given out by the signal over a set time period.
"You would analyse the sound bite from start to finish and view it visually on a graph. By analysing the contents and comparing it with a reference sample, you can match the voices and say whether or not it is the same person speaking," he said.
Grobbelaar said that in an ideal situation the person in question would be asked to give a sample recording, preferably with some of the phrases and words used on the original tape.
"That way you are sure you are comparing apples with apples. For a high probability match, you need as many words and phrases as possible to compare, and the more you have the more accurate your result will be," he said.