Can you hear me now?" asks the popular Verizon commercial. In audio analysis, the answer may well have been "Yes." But that didn't mean the evidence could be used. Limitations in first-generation audio analysis techniques and tools often prevented forensic analysts from making sense out of what they heard.
Advances in digital sound recording technology and audio analysis software have changed this. The restriction on audio forensic analysis traditionally has been the ability of software programs to manipulate sound data. Today's sophisticated software packages are a boon to forensic analysts because they permit analysis, manipulation and interpretation of audiotapes to recover information that in the past may have been lost. Now, complex analysis can even take place on older equipment, which has always been able to collect sound data - the limitation has typically been in the software.
Today's police departments and prosecutors understand valuable evidence often rests on an answering machine recording, cell phone message, 911 call tapes, etc. Most state crime laboratories and many private companies now perform audio forensic investigation. As the use of this evidence increases, "mum's the word" may take on new meaning among the criminal element, who may soon find what they say is as incriminating as what they do.
The value of audio evidence
Audio evidence was once overlooked because law enforcement lacked convenient means of analysis. This changed as federal funds became available to enhance forensic laboratories' ability to analyze both audio and visual evidence. In fact, the Department of Homeland Security has allocated funds for small- to mid-sized departments to add audio forensics capabilities.
A number of companies produce forensic audio analysis software packages. These vary in the types and depth of analysis they perform as well as in price, which can range from $400 to $1,500. Among the companies marketing this software are: Enhanced Audio Inc. of York, Pennsylvania; Cedar Audio of Portland, Maine; Clarifying Technologies of Raleigh, North Carolina; and Sound Forge, a division of Sony Corporation. (See "Establishing the audio/video forensic lab" on Page 140.)
But it's no panacea. It's true advances in electronic communications and security technology that have led to an increase in the number and types of audio recording devices (cell phones, video cameras, computer voicemail, cassette recorders and audio recording security cameras to name a few). However, in many cases the recording quality of the device itself remains relatively poor. While a recording may sound good to the average listener, the level of background noise, the ability to reliably reproduce speech frequencies without distortion and the audio frequency spectrum they can record are factors in obtaining an audio recording of sufficient quality for evidentiary purposes.
Don't spoil the evidence
Handling audio recordings and tapes is also a critically important factor in developing defensible audio evidence. As with all crime scene evidence, strict chain-of-custody rules and procedures must be adhered to. When a piece of audio evidence is found, it should be immediately placed in an evidence bag or appropriate container and shipped to the audio lab. Evidence should not be lugged around in a coat pocket for hours or left on the front seat of a closed squad car in 95-degree temperatures. This situation not only leads to evidence degradation but also can provide a point for the defense to question the data. Audio evidence also should not be copied to low-quality recording equipment. This evidence should only be reproduced and analyzed on certified equipment designed for audio forensic use.