Hennessey, J.
In this case of first impression in this Commonwealth, the single issue argued by the defendant concerns the judge’s allowing in evidence, from an expert witness introduced by the Commonwealth, opinions as to voice identification based in part on visual analysis of spectrograms, commonly referred to as “voiceprints.” We conclude that the evidence was properly admitted.
The defendant was convicted, after a jury trial, on three indictments charging him with the kidnapping and first degree murder of Paul Cavalieri, and extortion from the victim’s father.1 The appeal is under G. L. c. 278, §§ 33A-33G.
[193]*193The evidence in the case was as follows. Paul Cavalieri, thirteen years old, left his house in the early evening of November 2, 1972. He did not return home that night, or ever thereafter. Two days later the boy’s mother received a telephone call in which a voice said in a whisper, “you will receive instructions.” Although Mrs. Cavalieri had known the defendant for seventeen years, she did not recognize the voice.
With permission of the Cavalieris, a “tap” was placed on their telephone for the recording of incoming calls, and a so called “trap” was also placed on the telephone to assist in the tracing of such calls.
A few days after that, a ransom note was received demanding $50,000. In the ensuing several days, the victim’s father received several telephone calls all concerned with his son and the payment of ransom. He did not recognize the caller’s voice. Following instructions in the note and in the telephone calls, the father left the ransom money at two different locations; the money was not picked up. As a result of the third telephone call, he left the money at a new and different location. At 12:10 a.m. on November 10, 1972, a white male was observed by police picking up the money. Sometime later, and not far away, other officers observed a man carrying a white bag come out of the woods and get into a red station wagon. By tracing the vehicle, they learned the identity of the driver, one Tardiff. From him, they learned of the identity of the defendant as a person who, on a pretext, had persuaded Tardiff to leave the defendant on a highway near the place where the ransom had been left, and to pick up the defendant later, at a prearranged place.
The defendant was arrested. The police warned him of his constitutional rights in terms that are not now contested, as to adequacy, by the defendant. The [194]*194defendant admitted to the police that he had picked up the package, but he contended that he had done it for pay of $500 from a man in the drug traffic business. He denied having made telephone calls to the Cavalieris.
The defendant told of leaving the money where he had been instructed to by the man who had hired him. The police recovered the money later (not at the place told to them by the defendant), but rather as a result of information received from a man named Delaney, in whom the defendant had confided the location of the money. A package of black bags, identified as the same kind as the bag in which the ransom had been recovered by the police, was found in the defendant’s vehicle. The defendant’s personal effects and his automobile were stained by the dye that had been put on the ransom money.
On April 12, 1973, the body of Paul Cavalieri was found in a wooded area in North Attleborough. Death had been caused by gunshot wounds. In addition to the evidence outlined above, it was shown at trial that a .38 caliber Colt revolver had been found by police in the defendant’s apartment. An expert testified that the bullets found in the victim’s body could have been fired from that gun, as shown by rifling impressions on the bullets, but due to oxidation on the bullets there were not sufficient microscopic marks for identification. Ammunition for the gun was also discovered in the defendant’s apartment and this ammunition, like the bullets found in the victim’s body, was of a rare type. In addition, five staples found in the ransom note were examined and determined to be consistent in manufacture and size with a stapler and staples owned by the defendant. About the time of the victim’s disappearance, the defendant was admittedly near the place where, the victim was last seen alive. The defendant’s car was seen several times near the place where the “drop” of ransom money was first made, at the time when the money, in response to telephoned instructions, had been left at that location.
[195]*195Eight witnesses listened at the trial to one of the recorded telephone calls. Seven of these witnesses had heard the defendant speak on the telephone on prior occasions. Six of them identified the voice as that of the defendant. The eighth witness had not heard prior telephone talks of the defendant; he also identified the voice as that of the defendant. The witnesses were particularly definite in identifying certain words which were said, not in a whisper, but clearly. Only one of the eight witnesses, called as to this issue, could make no voice identification.
All of the “tapped” recorded telephone calls to the Cavalieris had been whispered, at least for the most part, by the caller. Several exemplars of the defendant’s voice reading the words of the previously recorded telephone calls, including exemplars in the defendant’s whispering voice, were given to the police. The telephone tapes and the exemplars were sent to Lt. Ernest W. Nash of the Michigan State police.
We turn now to the issue raised in these appeals: the admission in evidence of the voice identification opinions based on voice spectrograms. In an extensive voir dire hearing as to the admissibility of the evidence, Dr. Oscar Tosi, described as “a professor at Michigan State University and director of the Speech and Hearing Research Laboratory,” and Lt. Ernest W. Nash of the Michigan State police, described as “of the Voice Identification Unit, which is a unit of the Scientific Criminal Laboratory, stationed at East Lansing, Michigan,” both introduced by the Commonwealth, testified at length in support of the admissibility of the evidence. Of the two only Lt. Nash subsequently testified before the jury, after the judge had ruled that his expert opinions were admissible. Dr. Louis J. Gerstman, introduced by the defendant, testified in general that voice spectrogram analysis is unreliable and that, at this time, voice spectrograms should not be used as a means of identification in a forensic situation. No issue is raised as to the qualifica[196]*196tians of Lt. Nash, or, indeed, any of the three expert witnesses. The sole issue relates to whether the expert evidence of Lt. Nash offered here has been shown to be sufficiently reliable to be admissible in evidence.
In Commonwealth v. Fatalo, 346 Mass. 266, 269 (1963), and Commonwealth v. A Juvenile, 365 Mass. 421, 425-426 (1974), cases concerned with the admissibility of polygraphic evidence, we adopted the standard of admissibility as to expert opinions based on scientific discoveries as first stated in the case of Frye v. United States, 293 F. 1013, 1014 (D. C. Cir. 1923): “Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define.
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Hennessey, J.
In this case of first impression in this Commonwealth, the single issue argued by the defendant concerns the judge’s allowing in evidence, from an expert witness introduced by the Commonwealth, opinions as to voice identification based in part on visual analysis of spectrograms, commonly referred to as “voiceprints.” We conclude that the evidence was properly admitted.
The defendant was convicted, after a jury trial, on three indictments charging him with the kidnapping and first degree murder of Paul Cavalieri, and extortion from the victim’s father.1 The appeal is under G. L. c. 278, §§ 33A-33G.
[193]*193The evidence in the case was as follows. Paul Cavalieri, thirteen years old, left his house in the early evening of November 2, 1972. He did not return home that night, or ever thereafter. Two days later the boy’s mother received a telephone call in which a voice said in a whisper, “you will receive instructions.” Although Mrs. Cavalieri had known the defendant for seventeen years, she did not recognize the voice.
With permission of the Cavalieris, a “tap” was placed on their telephone for the recording of incoming calls, and a so called “trap” was also placed on the telephone to assist in the tracing of such calls.
A few days after that, a ransom note was received demanding $50,000. In the ensuing several days, the victim’s father received several telephone calls all concerned with his son and the payment of ransom. He did not recognize the caller’s voice. Following instructions in the note and in the telephone calls, the father left the ransom money at two different locations; the money was not picked up. As a result of the third telephone call, he left the money at a new and different location. At 12:10 a.m. on November 10, 1972, a white male was observed by police picking up the money. Sometime later, and not far away, other officers observed a man carrying a white bag come out of the woods and get into a red station wagon. By tracing the vehicle, they learned the identity of the driver, one Tardiff. From him, they learned of the identity of the defendant as a person who, on a pretext, had persuaded Tardiff to leave the defendant on a highway near the place where the ransom had been left, and to pick up the defendant later, at a prearranged place.
The defendant was arrested. The police warned him of his constitutional rights in terms that are not now contested, as to adequacy, by the defendant. The [194]*194defendant admitted to the police that he had picked up the package, but he contended that he had done it for pay of $500 from a man in the drug traffic business. He denied having made telephone calls to the Cavalieris.
The defendant told of leaving the money where he had been instructed to by the man who had hired him. The police recovered the money later (not at the place told to them by the defendant), but rather as a result of information received from a man named Delaney, in whom the defendant had confided the location of the money. A package of black bags, identified as the same kind as the bag in which the ransom had been recovered by the police, was found in the defendant’s vehicle. The defendant’s personal effects and his automobile were stained by the dye that had been put on the ransom money.
On April 12, 1973, the body of Paul Cavalieri was found in a wooded area in North Attleborough. Death had been caused by gunshot wounds. In addition to the evidence outlined above, it was shown at trial that a .38 caliber Colt revolver had been found by police in the defendant’s apartment. An expert testified that the bullets found in the victim’s body could have been fired from that gun, as shown by rifling impressions on the bullets, but due to oxidation on the bullets there were not sufficient microscopic marks for identification. Ammunition for the gun was also discovered in the defendant’s apartment and this ammunition, like the bullets found in the victim’s body, was of a rare type. In addition, five staples found in the ransom note were examined and determined to be consistent in manufacture and size with a stapler and staples owned by the defendant. About the time of the victim’s disappearance, the defendant was admittedly near the place where, the victim was last seen alive. The defendant’s car was seen several times near the place where the “drop” of ransom money was first made, at the time when the money, in response to telephoned instructions, had been left at that location.
[195]*195Eight witnesses listened at the trial to one of the recorded telephone calls. Seven of these witnesses had heard the defendant speak on the telephone on prior occasions. Six of them identified the voice as that of the defendant. The eighth witness had not heard prior telephone talks of the defendant; he also identified the voice as that of the defendant. The witnesses were particularly definite in identifying certain words which were said, not in a whisper, but clearly. Only one of the eight witnesses, called as to this issue, could make no voice identification.
All of the “tapped” recorded telephone calls to the Cavalieris had been whispered, at least for the most part, by the caller. Several exemplars of the defendant’s voice reading the words of the previously recorded telephone calls, including exemplars in the defendant’s whispering voice, were given to the police. The telephone tapes and the exemplars were sent to Lt. Ernest W. Nash of the Michigan State police.
We turn now to the issue raised in these appeals: the admission in evidence of the voice identification opinions based on voice spectrograms. In an extensive voir dire hearing as to the admissibility of the evidence, Dr. Oscar Tosi, described as “a professor at Michigan State University and director of the Speech and Hearing Research Laboratory,” and Lt. Ernest W. Nash of the Michigan State police, described as “of the Voice Identification Unit, which is a unit of the Scientific Criminal Laboratory, stationed at East Lansing, Michigan,” both introduced by the Commonwealth, testified at length in support of the admissibility of the evidence. Of the two only Lt. Nash subsequently testified before the jury, after the judge had ruled that his expert opinions were admissible. Dr. Louis J. Gerstman, introduced by the defendant, testified in general that voice spectrogram analysis is unreliable and that, at this time, voice spectrograms should not be used as a means of identification in a forensic situation. No issue is raised as to the qualifica[196]*196tians of Lt. Nash, or, indeed, any of the three expert witnesses. The sole issue relates to whether the expert evidence of Lt. Nash offered here has been shown to be sufficiently reliable to be admissible in evidence.
In Commonwealth v. Fatalo, 346 Mass. 266, 269 (1963), and Commonwealth v. A Juvenile, 365 Mass. 421, 425-426 (1974), cases concerned with the admissibility of polygraphic evidence, we adopted the standard of admissibility as to expert opinions based on scientific discoveries as first stated in the case of Frye v. United States, 293 F. 1013, 1014 (D. C. Cir. 1923): “Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs” (emphasis added).
In the Fatalo case, supra, at 269, we said: “Judicial acceptance of a scientific theory or instrument can occur only when it follows a general acceptance by the community of scientists involved. When supported by substantial authority establishing scientific reliability, this court has not hesitated to accept the benefits of science.” See also Commonwealth v. Stappen, 336 Mass. 174, 176-177 (1957), and Commonwealth v. Devlin, 365 Mass. 149, 153, fn. 3 (1974).
In accordance with the standards articulated in the Fatalo case, we, as a preliminary matter, consider the nature of the scientific machine involved. Like some other scientific devices, a spectrographie machine signifies its results by producing graphic patterns on a paper, patterns which are then the subject of analysis by the examiner. The spectrogram portrays three main parameters of speech: time (horizontal axis), frequency (vertical axis), [197]*197and relative amplitude or intensity (degree of shading in the different time/frequency regions). Identification is attempted by both aural and visual means. The operator compares voices by listening to recordings of known and unknown voices, and by visually analyzing high-speed sound spectrograms of each voice. If he finds sufficient points of similarity, he will indicate that two voice exemplars were made by the same person.
The examiner thus draws his conclusions not only from a visual but also from an aural comparison. It can be said that, at least in these aspects and considering the relative importance of subjective reasoning by the examiner, the process bears a closer resemblance to polygraph testing than it does to fingerprint or handwriting analysis. In some important respects, however, the claims made in support of the polygraph are fundamentally different from those made for the spectrograph, and in those distinctions lies part of our reasoning in treating the two differently. Most important is the breadth of the inference urged from the reading of the respective machines. Relying in part on voice characteristics demonstrated and measured by the spectrograph, the examiner there seeks to do no more than compare voices. In contrast, from the measurements reflected by the polygraph, the examiner then extrapolates to arrive at a judgment of something not directly measured by the machine, that is, the credibility of the person examined. In so doing, polygraphic evidence, with its purported ability to discern truth in testimony, may constitute, in any case, a force which intrudes far into the jury’s most important functions of determining credibility of witnesses and finding facts. We are aware that scientific proof may in some instances assume “a posture of mystic infallibility in the eyes of a jury of laymen.” United States v. Addison, 498 F. 2d 741, 744 (D. C. Cir. 1974). For the reasons we have cited, that consideration does not lead us to exclude the voice identification opinions here nor to impose so restrictive a standard of admis[198]*198sibility as we applied to polygraphic evidence in Commonwealth v. A Juvenile, 365 Mass. 421 (1974).
In reaching our conclusion that the evidence was properly admitted, we have examined relevant decisions from other jurisdictions; relevant writings in scientific journals and other sources; and the evidence produced at the trial as to reliability and general acceptance of the principle. We start with the concepts that neither infallibility nor unanimous acceptance of the principle need be proved to justify its admission in evidence.
As to the judicial acceptance of spectrography, it is undoubtedly more useful to consider the holdings of various courts since the year 1971 than prior thereto. The conclusions from two years of extensive laboratory tests supervised by Dr. Tosi were first made available in 1971. No comparable study was made before or has been made since this one.
Of the appellate courts which have considered the admissibility issue since these results were published, courts in three States (Minnesota, Florida, and California) have ruled that such voice identification evidence is admissible: State ex rel. Trimble v. Hedman, 291 Minn. 442 (1971) (voiceprints admissible to establish probable cause and for corroborative purposes); Worley v. State, 263 So. 2d 613 (Ct. App. Fla. 1972) (voiceprints properly admitted to corroborate voice identification); Alea v. State, 265 So. 2d 96 (Dist. Ct. App. Fla. 1972); Hodo v. Superior Court, 30 Cal. App. 3d 778 (1973). In addition, the Supreme Court of New Jersey indicated that growing acceptance of the technique might prompt it to reconsider its prior rejection of the evidence. State v. Andretta, 61 N. J. 544 (1972).2 Two appellate courts [199]*199which have ruled since the Tosi study have decided that the evidence is inadmissible. United States v. Addison, 498 F. 2d 741 (D. G. Cir. 1974). People v. Law, 40 Cal. App. 3d 69 (1974). The Law case goes no further than to say that such evidence is not admissible where the voice to be identified was disguised or mimicked.
Literature of the field does not reflect unanimous approval of the technique on the part of those who, from their writings, claim to be qualified to speak. Favorable comments in strong support have, of course, been written in the reports of the studies directed by Dr. Tosi. While some scientists have written in approval, others appear from their writings to have serious reservations as to the issue of admissibility.3
[200]*200The voir dire hearing as to admissibility conducted by the judge in this case was lengthy and comprehensive. Evidence reflected not only the qualifications and opinions of Dr. Tosi and Lt. Nash, but also appraised the qualifications (or lack of same) of those who have written in opposition to the use of the spectrograph in voice identification. At the hearing, a substantial showing of reliability was made from the results of the Tosi labora[201]*201tory experiment which culminated in 1971. In that study a total of approximately 35,000 trials of identification were conducted. The 250 speakers, all males, and all English speaking, were selected at random from a homogeneous population of students at Michigan State University. Visual examinations of spectrograms were conducted by twenty-nine trained examiners. Results, as published, indicated an error of six per cent false identifications and approximately twelve per cent false eliminations. Other correlated and detailed opinions as recorded by the examiners supported a conclusion that, if the examiners had been able to express no opinion when in doubt, errors of identification would be about two per cent.
From the testimony of Dr. Tosí and Lt. Nash the trial judge could well conclude that forensic experience of the witnesses, since the major laboratory study, had reduced the chance of error in their findings to a negligible amount. First, it was shown that the “real life” examiner listens to the voices in addition to visually inspecting the spectrograms, and it is the combination of both aural and visual comparison which enhances reliability.4 Second, the forensic examiner has experience and training in audiology and speech science beyond that of a usual laboratory worker. Third, the professional [202]*202examiner, unlike the laboratory worker, can take all the time he wants to make his decision, and he can examine and reexamine all the words he believes to be necessary, if these words are available for study. Fourth, the professional examiner, unlike the laboratory examiner, can select any one of several alternative types of decisions and, most important, he is free to choose to come to no decision in any given case. Lieutenant Nash testified that he had examined forensically 3,300 voices in the hope of identifying them; that he had positively eliminated slightly more than 1,900 of them, and had positively identified only slightly more than 500 of them. He thus came to no decision in almost a third of the cases.
All of these conclusions have bearing on the evaluations of the criticism leveled by those writers who oppose use of spectrography in judicial identifications. For the most part they contend that the percentage of error will increase when conditions depart from the laboratory and are considered in the real world. To the extent that a convincing case is made, as in this case, that the professional examiner will achieve more reliable results than the laboratory examiner, then to that extent the opposition can be discounted.
The requirement, as in the Frye and Fatalo cases of general acceptance in the scientific community assures that those most qualified to assess the general validity of a scientific method will have the determinative voice. See United States v. Addison, 498 F. 2d 741, 743-744 (D. C. Cir. 1974). Additionally, the application of the rule protects the parties by assuring a reserve of experts who may be needed to testify.
It can be argued that both of these goals are endangered when only a limited number of persons claim [203]*203special knowledge in the field, as appears to be the case with spectrography. Limited in number though the experts may be, the requirement of the Frye rule of general acceptability is satisfied, in our opinion, if the principle is generally accepted by those who would be expected to be familiar with its use. In admitting evidence of a procedure called the Nalline test it was said: “No experts were called by the defendants and the expert testimony as above summarized stands uncontradicted in the record with this exception: Each of the People’s experts did admit on cross-examination that the medical profession generally is unfamiliar with the use of Nalline and therefore it cannot be truthfully said that the Nalline test has met with general acceptance by the medical profession as a whole, general acceptance being at present limited to those few in a specialized field who deal with the narcotic problem. Should this fact render the testimony inadmissible? We believe not. All of the medical testimony points to the reliability of the test. It has been generally accepted by those who would be expected to be familiar with its use. In this age of specialization more should not be required” (emphasis added). People v. Williams, 164 Cal. App. 2d Supp. 858, 861-862 (1958).
It has been suggested that the requirement of general acceptance, as in the Frye and Fatalo cases, should be modified or abandoned.5 See McCormick, Evidence § 203, p. 491 (2d ed. 1972), where it is said, “‘General scientific acceptance’ is a proper condition for taking judicial notice of scientific facts, but not a criterion for the admissibility of scientific evidence. Any relevant conclusions which are supported by a qualified expert [204]*204witness should be received unless there are other reasons for exclusion.” The suggestions by this author and others (see the concurring opinion of Mager, J., in the Worley case, supra, 263 So. 2d 613, 615 [1972]) urge that the opinions of a qualified expert should be received and that the considerations similar to those expressed in the Frye and Fatalo cases should be for the fact finder as to weight and value of the opinions.
There is no need for modification of the general principle of the Frye or Fatalo cases in order to uphold the judge’s ruling in this case. Examination of (1) the evidence as to admissibility presented before the judge, (2) judicial opinions from other jurisdictions, and (3) relevant scientific writings provides convincing proof to justify admission of the evidence. The considerable reliability proved by the Tosi experiment, the greatly added reliability induced by the application of further skills by the experienced examiner working under forensic conditions, and the totality of the evidence received at the voir dire hearing which tended to minimize the importance and weight of adverse or skeptical writings all serve to support a conclusion of general acceptability as required by the rule of the Fatalo and Frye cases.6
[205]*205We hold that there was no error in the admission of the contested opinions of Lt. Nash. Nothing that we have said in this opinion is intended to narrow the discretionary function of the trial judge in appraising the qualifications of an expert witness, or in excluding expert opinions for other reasons within the judge’s traditional area of discretion. We add that the admission of expert testimony as to spectrographie analysis should be subject to the closest of judicial scrutiny, particularly in any case where there is an absence of evidence of voice identification other than that of the voiceprint or where, but for the voiceprint, there would be insufficient evidence to warrant any inference of the defendant’s guilt. And, of course, as is traditional, once the voiceprint is admitted in evidence the jury may give it such weight as they deem proper.
We have reviewed the entire record in accordance with our duties under G. L. c. 278, § 33E, and we observe nothing which in justice indicates that we should modify the results reached by the jury.
Judgments affirmed.