The case for aural perceptual speaker identification.

Once forensic speaker identification (SI) was recognized as an entity, it was predicted that valid computer based identification systems would quickly become a reality. This has not happened and the review to follow will provide some of the reasons why. Notable among them are (1) the sharp underestimation of its complexity and (2) its confounding with speaker verification (SV). Consideration of these (and related) issues will be followed by a brief history about how the need for SI developed and some of the responses to the problem. Since much of the SI development preceded the structuring of appropriate standards, the recommended stop-gap response described here is based on somewhat uncoordinated, but extensive, research. The product of that effort will be reviewed and organized into a platform which supports SI procedures consistent with the forensic model. Also discussed are the standards which have been established, their impact on SI development and its present limitations. How the cited approach interacts both with progress in verification and the developing SI machine-based identification systems also will be considered. Finally, a few suggestions will be made that should assist in upgrading the effectiveness of aural perceptual speaker identification (AP SI).

An Approach to Speaker Identification.

This presentation will provide standards upon which any attempts to meet the challenge of identifying speakers by voice should be based. It is organized into a model based on (i) application of a rigorous research program validating the system, (ii) an upgrading of the organization of the SI area, and (iii) exploitation of new technology. The second part of the presentation will describe an illustrative speech/voice approach to SI development. This effort is also based on an extensive corpus of research. It is suggested that application of the cited standards, plus the illustrative model, will permit reasonable progress to be made. Finally, a number of procedural recommendations are made; they should enhance the efficacy of the proposed approach.

Vocal fold dynamics for frequency change.

This article provides a review of data drawn from a series of related experiments to demonstrate how frequency change (Δf0) is accomplished in the modal register. The research cited involves studies of (1) laryngeal size, (2) vocal fold length, (3) vocal fold thickness, and (4) subglottic pressure; new data describe their effect on vocal fold mass. It was found that changes in these dimensions (1) explain how the shifts in frequency are accomplished, (2) establish the way vocal fold mass can be measured, and (3) strongly support the aerodynamic-myoelastic theory of phonation.

Issues in forensic voice.

The following article provides a general review of an area that can be referred to as Forensic Voice. Its goals will be outlined and that discussion will be followed by a description of its major elements. Considered are (1) the processing and analysis of spoken utterances, (2) distorted speech, (3) enhancement of speech intelligibility (re: surveillance and other recordings), (4) transcripts, (5) authentication of recordings, (6) speaker identification, and (7) the detection of deception, intoxication, and emotions in speech. Stress in speech and the psychological stress evaluation systems (that some individuals attempt to use as lie detectors) also will be considered. Points of entry will be suggested for individuals with the kinds of backgrounds possessed by professionals already working in the voice area.

On pubescent voice change in males.

This review of adolescent voice change (AVC) in males is introduced by a brief historical overview of the area. That effort is followed by a summarization of those core studies which describe the AVC process in the normal boy. Although no new experiments are presented, a number of related investigations are organized into a cohesive base-one that permits development of an AVC model The model, then, can be employed to establish a reasonable description of the process by providing information about its initiation, duration, and completion. It also assists in establishing perspectives about pubescent voice change and a baseline for future research.

Perceiving the effects of ethanol intoxication on voice.

Many conditions operate to degrade the quality of the human voice. Alcohol intoxication is one of them. In this project, the objectives were to examine the ability of human listeners to accurately estimate both the presence and severity of intoxication from two types of speech samples. A review of available data suggests that, although listeners can often identify individuals who are intoxicated simply by hearing samples of their voice, they are less efficient at accurately determining the severity of this condition. A number of aural-perceptual studies were carried out to test these relationships. Populations of speakers, selected based on rigorous criteria, provided orally read and extemporaneous utterances when sober and at three highly controlled levels of intoxication. Listener groups of university students and professionals attempted to identify both the existence and specific level of intoxication present. It was found that these individuals were proficient in recognizing the presence of, and increases in, intoxication but were less accurate in gauging the specific levels. Several subordinate relationships were also investigated. In this regard, statistically significant differences were not found between male and female listeners or between professionals and lay listeners; however, they were found for different classes of speech. That is, it was shown that text difficulty correlated with severity of effect.

Stress and deception in speech: evaluating layered voice analysis.

This study was designed to evaluate commonly used voice stress analyzers--in this case the layered voice analysis (LVA) system. The research protocol involved the use of a speech database containing materials recorded while highly controlled deception and stress levels were systematically varied. Subjects were 24 each males/females (age range 18-63 years) drawn from a diverse population. All held strong views about some issue; they were required to make intense contradictory statements while believing that they would be heard/seen by peers. The LVA system was then evaluated by means of a double blind study using two types of examiners: a pair of scientists trained and certified by the manufacturer in the proper use of the system and two highly experienced LVA instructors provided by this same firm. The results showed that the "true positive" (or hit) rates for all examiners averaged near chance (42-56%) for all conditions, types of materials (e.g., stress vs. unstressed, truth vs. deception), and examiners (scientists vs. manufacturers). Most importantly, the false positive rate was very high, ranging from 40% to 65%. Sensitivity statistics confirmed that the LVA system operated at about chance levels in the detection of truth, deception, and the presence of high and low vocal stress states.

Evaluation of the NITV CVSA.

The purpose of this study was to evaluate a commonly used voice stress analyzer, the National Institute of Truth Verification's (NITV) Computer Voice Stress Analyzer (CVSA), using a speech database containing materials recorded (i) in the laboratory, while highly controlled deceptive and shock-induced stress levels were systematically varied, and (ii) during a field procedure. Subjects were 24 each males/females (age range 18-63 years) drawn from a representative population. All held strong views on an issue and were required to make sharply derogatory statements about it. The CVSA system was then evaluated in a double-blind study using three sets of examiners: (i) two UF scientists trained/certified by NITV in CVSA operation, (ii) three experienced NITV operators provided by the manufacturer and (iii) five experimental phoneticians. The results showed that the "true positive" (or hit) rates for all examiners ranged from chance to somewhat higher levels (c. 50-65%) for all conditions and types of materials (e.g., stress vs. unstressed, truth vs. deception). However, the false-positive rate was just as high - often higher. Sensitivity statistics demonstrated that the CVSA system operated at about chance level.

Speaking rate and fundamental frequency as speech cues to perceived age.

This study aimed to specify a set of acoustic cues fundamental to vocal aging and to establish their perceptual relevance, using acoustic analysis and perceptual testing. Three experiments were conducted to identify the perceptual correlates of the aging voice. The first experiment analyzed important voice parameters that signal a person's age for 16 older males and 14 younger males. In the second and third experiments, these acoustic patterns were systematically shifted through resynthesis to see if perceived age would be significantly influenced. In the second experiment, the older and younger male voices were resynthesized by manipulating speaking rate and fundamental frequency to shift the perceived age of the groups toward each other. In the third experiment, older and middle-aged male voices were resynthesized in a similar manner. In both perceptual studies, an age estimation task with naive listeners was used. The results of the first experiment showed that, in older speakers, sentence, word, and diphthong durations were all significantly longer and mean fundamental frequency was significantly higher than for the younger group. In the second experiment, only the manipulation of speaking rate resulted in a significant shift in perceived age, and it did so only for the older subjects. In the third experiment, a significant shift in age estimates was observed for the middle-aged, but not the older, voices when speaking rate was manipulated. The results of both perception tests suggest that speaking rate, but possibly not fundamental frequency, is a perceptually relevant cue to age in voice.

The false vocal folds: shape and size in frontal view during phonation based on laminagraphic tracings.

The geometry of the false vocal fold region during phonation is important to the understanding of the aerodynamics and acoustics of voice. The shape and dimensions of this region during phonation were estimated using laminagraphic tracings of the larynx. Laminagrams from two previous studies, one with non-singer subjects (Experiment I, Hollien and Colton, 1969) and the other with singers (Experiment II, Wilson, 1972), were traced, photocopied, and measured. Statistical analysis showed significantly greater false vocal fold height in males than females for both experiments. The false vocal fold gap was also significantly greater in males than females for Experiment II, but reached only borderline significance for Experiment I. For each gender, most of the linear measures were greater in Experiment I when compared to Experiment II; these differences may be passive in nature (due to actual differences in subject size) or active (due to muscle contraction that displaced the false vocal folds during singing).