Monday, December 15, 2008

Biometric Uniqueness

So you think you’re unique? Modern technology has affirmed what theologians have always known in a spiritual sense: Each of us is unique in the eyes of our Creator. That uniqueness also includes many different physical characteristics. A methodology called biometric verification has expanded far beyond the long-known handwriting analysis and fingerprinting. In the past few decades we have added, among others, voice prints, iris scanning, and DNA as identification tools. The latter two are as close to a sure thing as one could get. The chances of misidentification using them are virtually zero. The first method mentioned, voiceprints, graphically analyzes vocal sounds in a variety of ways. There is a musical quality associated with many of the sounds we hear, so I’ll use musical instruments to illustrate the point.

Consider a plucked violin string. Making our math easy, consider a string which vibrates back and forth 100 times per second. It would produce a sound of 100 hertz, displacing our eardrums 100 times per second. We would hear a “fundamental” pitch of 100 hz. The violin string would also vibrate in two parts, three parts, four parts, and so on. These string sections would produce pitches of 200 hz, 300 hz, and 400 hz, respectively, called overtones. The 200 hz tone is one octave higher, and each successive tone is higher, but by a smaller and smaller musical interval. What do we hear when the string is plucked? We hear only the pitch of 100 hz, but its sound is enriched and made unique by the overtones. Each instrument, when producing a pitch of 100 hz, sounds different from any other instrument because of the differing proportions and intensity of its overtones.

When I learned to play a baritone horn in high school, I quickly discovered that I could play many successive higher notes, without changing the fingering, just by tightening my lips in the mouthpiece. That’s because the entire column of air inside the horn was also vibrating as a half column, a one-third column, a one-fourth column, and so on. I could make the overtones sound alone by altering the mouthpiece conditions. Bugle players have no valves at all in their instruments. They create their melodies using only overtones, but they are limited to a smaller number of playable notes.

How many different human voices can you recognize? Dozens? Hundreds? The vocal cords and voice box of each person you know produce overtones slightly different from anyone else because the thickness, length, and physical quality of each person’s vocal cords are different from anyone else. This results in an endless variety of musical and vocal abilities and characteristics among our acquaintances. In other words, each person’s voice is unique. Beyond the physical processes of sound production, the miracle of the hearing process gives us even greater reason to acknowledge God’s wonders. This is a subject for a future post.