Simple Acoustics

Abstract

Much of the material contained in this book involves the use, analysis and/or understanding of sound. For example, if we were to analyze the speech contained on a tape recording resulting from an electronic surveillance, the “material” we would process is the acoustic signal of that conversation which was captured on magnetic tape. How did it get there? Or to be more specific: what is its nature; what are its features; what are the actual codes it contains? Yet another example: let us say that we are attempting to evaluate a tape recording to see if it is authentic or has been modified in some manner. All of the sounds we can hear when the tape is played have been created by either some sort of acoustic event or electronic disturbance; we must understand their nature if we are to make valid judgments of authenticity. Another example can be found in the case I will call “Watch Out For Your Relatives.” A caller attempted to extort money from a wealthy women. She recorded the second of several calls, which she believed was made by one of her nephews. The stored acoustic signals (the telephone call) and the exemplars later made of the nephews’ voices (as well as those of foils, or controls) became the basis of a speaker identification task. The outcome was that one of the nephews was identified as the extortionist. All of these examples relate in some manner to basic acoustics; indeed, the list that could be provided is a very long one. The items cited simply illustrate the fact that an individual must have a basic understanding of acoustics if he or she is going to comprehend and/or carry out the many different processes and procedures described in this book.