babble tapes have been used less by mobsters than by attorneys concerned that eavesdropping may violate attorney-client privilege. A babble tape is a digital file meant to be played in the background during conversations. The file is complex. Forty voice tracks run simultaneously (thirty-two in English, eight in other languages), and each track is compressed in frequency and time to produce additional “voices” that fill the entire frequency spectrum. There are also various non-human mechanical noises, and a periodic supersonic burst (inaudible to adult listeners) engineered specifically to interfere with the automatic gain-control system of an eavesdropping device configures itself to best pick up an audio signal. Most pertinent for present purposes, the voices on a babble tape used by an attorney include those of the client and the attorney themselves. The dense mélange of voices increases the difficulty of discerning any single voice.
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