Voiceprint, a visual representation of a person's voice used for purposes of identification. A voiceprint is made with a sound spectrograph, a device used to analyze complex sound waves. The voiceprint appears as a pattern of tracings that indicate the moment-by-moment distribution and relative strengths of a voice's component frequencies. The voiceprints of different people speaking the same words generally show patterns unique to each speaker. Unlike fingerprints, however, voiceprints made at different times (of the same person speaking the same words) may show some variation. Voiceprints were first used as evidence in a court of law in 1966.
The terrorist attacks of Sept. 11, 2001, had a profound effect on the United States -- and the world. Trace the progression of events in this timeline.
If you need an analogy for PRISM, one apt comparison would be to HBO's show "The Wire." Just swap "U.S. government" for Baltimore police, "Internet data" for phone wiretaps, and name the target as "really anyone" instead of drug traffickers. Got it?