Be cause the voice, like handwriting, is dynamic and variant, several samples of each spoken phrase are desired for analysis. Unless the questioned call sounds like a read statement, the suspect should not be allowed to read the phrases from a transcript but should repeat each phrase after it is spoken by someone else. To avoid an unnatural verbal response, the suspect should repeat the first phrase and proceed in the same manner with each successive phrase. When all phrases have been record ed, the same procedure should be repeated at least two more times beginning with the first word or phrase. The suspect may be asked to read the phrases if a very poor job of repeating is done.
Some people do a better job of reading than repeating the phrases.
If the caller's voice was disguised, the suspect should give a normal sample and a disguised one as in the questioned call. Recorded evidence should be wrapped in tinfoil to protect it from possible contact with a magnetic field if it is submitted by mail. The evidence should be shipped in a secure container that will prevent the evidence from tearing through the packaging material. Do not submit a copy of your investigative report with the evidence. The examiner does not want to know the details of the case.