This cause has been remanded for a pretrial hearing to determine whether the voiceprint technique in voice identification and the equipment producing the print have sufficient scientific acceptance whereby they produce uniform and reasonably reliable results and will contribute materially to the ascertainment of the truth, and as such is admissible as evidence. State v. Cary, 49 N.J. 343, 352 (1967).
Spectrogram voice identification is a recently developed technique that allegedly is able to identify a person from graphic representations of his voice. If reliable as an identification tool it will have enormous potential as a forensic aid.
The sound spectrograph with which we are here concerned was first developed at Bell Laboratories in this State about 1941. The instrument produces a permanent spectrogram, which is a graphic display of complex signals. The spectrograph is a basic research instrument used in many laboratories for research studies of sound, music and speech.
Voiceprint identification is the method by which a person can be identified from a spectographic examination of his taped voice, the spectrograph being capable of reproducing graphic impressions from tapes of human utterances. Specifically, ten frequently used cue words are normally involved: the, to, and, me, on, is, you, I, it, a. When the source material from which the voice is to be identified is contextual, these specific cue words are excerpted and compared with previously recorded voiceprints of or containing the same cue words.
The basic principle underlying the use of the voiceprint method is that whenever a sound is uttered, an energy output is required to transform it into an intelligible word. This energy output is electronically recorded on a sound spectrograph from the tape recording in the one-tenth of a second that it takes to utter the sound, and is thereafter transferred by the spectograph into a "contour" or "bar" print. The print is a visual representation of the utterance.
The voiceprint can then be used for comparison and identification purposes.
There are two basic types of voiceprints: (a) "bar" and (b) "contour." Both types may be the result of a person uttering a cue word or other words as taped. The "bar" voiceprint shows the resonance bars of the person's voice. The pattern of the bars determines what word is being said. In addition thereto, the voiceprint has dimensions of time (plotted from left to right, i.e., the beginning of the word is at the left and the end is at the right); the frequency is plotted along the vertical axis (the lower pitch of sound appears at bottom and higher pitch toward the top); and the loudness is ascertained by examining the blackness of the printing (the darker lines of the bar represent greater intensity of sound at each frequency for a particular time).
The "contour" voiceprint is identical with the "bar" print with regard to time and frequency measurements. The level of loudness, however, differs somewhat from that of the "bar" print. The various contours or "peaks" indicate the changes in intensity of sound at each frequency for a particular time. It has been suggested by an expert in the field of voiceprinting that it is easier to detect patterns of the "bar" voiceprint, but that the "contour" voiceprint is more easily analyzed and is also more easily reproduced in print.
The inquiry in this area is whether identification by a voiceprint has the claimed validity and, if so, to what degree? In other words, having several voiceprints, among which there are two made by the same person, can a trained individual, by reading, comparing and analyzing the spectrogram, determine with a high degree of certainty which of those voiceprints are of the same person; or having a known print to be compared with an unknown print, can it be reliably determined that it is or is not the voice of the same person; or having a pre-identified print that is to be compared with an unidentified print, can it be reliably determined that the two prints are or are not voiceprints of the same person's voice? Can the utterances of two or more persons produce
the same print? Is the technique generally recognized by the scientific ...