Some background is important for understanding the admissibility of expert testimony on new technology, because several court cases have challenged and refined admissibility procedures.  Throughout legal history, problems have arisen in the courtroom when novel information was presented that seemed difficult to evaluate for its accuracy, so rules were devised for deciding whether the evidence presented ought to have legal weight.

Before examining specific spectrograph-relevant cases, a look at the evolution of judicial procedure regarding scientific evidence helps to understand what the courts have said about voiceprints.

In 1923, the District of Columbia Court of Appeals issued an opinion that became the guideline for the admissibility of scientific evidence.  In a case know as Frye, the defense counsel tried to enter evidence about a device that measured blood pressure during deception (a forerunner to the polygraph).  The court decided that the thing from which the testimony is deduced must be "sufficiently established to have gained general acceptance in the particular field in which it belongs."  It also had to be determined that the information was beyond the general knowledge of the jury.  This Frye standard became general practice in most courts and continued to influence decisions for many years.  It prevented courts from running mini-trials about the scientific evidence itself.

However, critics claimed that the Frye standard excluded theories that were novel but nevertheless supported by evidence.  In 1975 the Federal Rules of Evidence became effective and Rule 702 states: "If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training or education, may testify thereto in the form of an opinion or otherwise."   However, the courts varied greatly in the way they followed this standard.

The Frye test was more effectively replaced in many states by a standard cited in 1993 in the Supreme Court's decision in Daubert v. Merrill Dow Pharmaceuticals, Inc., which emphasizes the trial judge's responsibility as a gatekeeper.  The court decided that "scientific" means having a grounding in the methods and procedures of science, and "knowledge" must be stronger than subjective belief or unsupported speculation.  The judge has only to focus on the methodology, not on the conclusion, and also must decide whether the scientific evidence applies to the facts of the case.  In other words, judges have to determine:

• whether the theory can be tested
• whether the potential error rate is known
• whether it was reviewed by peers and has attracted widespread acceptance within a relevant scientific community
• Whether the opinion is relevant to the issue in dispute.

With voice spectrography, the National Academy of Science concluded in 1979 that, "The degree of accuracy and the corresponding error rates of aural-visual voice identification vary widely from case to case."  In other words, the graph interpretation was viewed as lacking in standards, the equipment quality could be suspect, and the conditions under which a voice sample is taken vary so much as to have a significant impact on the identification procedure.  The same goes for the knowledge and skill of the interpreter. That meant that there appeared to be no adequate scientific basis for bringing the results into court as sufficiently reliable for judges or juries to make just decisions based upon it.

Nevertheless, this technology has been introduced in court in every state and only Maryland does not allow spectrograph evidence.

Despite rulings in states like New Jersey and California, which used Frye as a guideline, courts in Florida admitted spectrograms in 1972 as corroborative evidence: As long as other methods of identifying a suspect were used, voiceprints could be brought in.  Eventually courts across the country began to yield as more and more experts came in to verify the reliability of the machine.  Courts were especially impressed with the testimony of Dr. Oscar Tosi, who initially had testified against the use of the spectrograph.  After extensive research of his own, he had switched his position and declared it to be highly reliable.

However, in a California case, People v. Law, the appellate judge reversed a conviction, which was gained with the help of a spectrogram, based on the fact that no study had been carried out to test the effects on voiceprints of disguised or mimicked voices.

Nevertheless, courts eventually gave greater weight to the testimony of those experts who had direct empirical experience in the field than to academic critics.  Voiceprint technology did not have to prove to be infallible to be accepted as evidence.  In the case of Reed v. State, the definition of "scientific community" was broadened to include people who had sufficient scientific background to understand the process in question and form a judgment about it.  That decision assisted admissibility.    

As voiceprint technology and interpretations become more widely used, increasingly more courts are responding favorably to it.  Nevertheless, it remains an unsettled question, in particular when courts review older decisions based on the technology in its early stages.

"People are generally misinformed about voice identification," Tom Owen says.  "I've never failed to qualify as an expert witness, nor failed to be heard in a case.  Those who say that this technology is not accepted really have no clue.  The only courts that have rejected it, did so in the seventies on the basis of the Frye hearings.  It's decided on a case-by-case basis, but the only scientific community that counts for consensus is the community that is engaged in doing the work.  In every case where someone has offered counter-testimony, that person was a teacher from a local college who did not actually participate actively in spectrographic analysis.  They should not be considered part of the scientific community that is doing the work."

Owen also points out that the trial decisions in the seventies were based on testimony from technicians who only used the voiceprint.  "Now law enforcement primarily uses the aural spectrographic method, which means we listen to the tape first and then do the spectrograph.  The American College of Forensic Examiners, which now controls who gets certified, has taken the position that the only way to do this is the aural spectrographic method.  You have to actually listen to the tape, not just look at the graph."

Certain precautions are observed during trials that provide clear context for the evidence and that work to ensure that all such testimony is properly understood.  Juries are allowed to see the voiceprint and hear the tape recordings.  The other side scrutinizes the expert's qualifications and the machine's quality.  In the end, the jury is generally instructed to assign whatever weight they want to the evidence.  That means that a lot will depend on the experience and demeanor of the voiceprint expert.  To be convincing he or she needs proper training.