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 On the day in engineering history, President Richard M.
Nixon agreed to comply with a Congressional subpoena which required him to surrender
audio tapes of his Oval Office conversations about the Watergate scandal, a
massive campaign of political spying and sabotage. In February of 1971, Nixon
had ordered the Technical Services Division of the U.S. Secret Service to
install a recording system in his White House office. Secret service agents
placed line-taps on the telephones and installed hidden microphones around the
President's office. Later, after two Washington
Post reporters learned about a break-in at Democratic National Committee
headquarters, a White House aid revealed the existence of the White House
recording system during Congressional testimony.
Dictaphones and DictaBelts
To record telephone conversations, the White House recording
system used a series of DictaBelt machines. These sound-recording devices were
introduced by the American Dictaphone Company in 1947, and soon replaced many older
dictation devices that used wax cylinders as their recording medium. The name "Dictaphone"
is a trademark of their inventor, but has become a common way to refer to all
such dictation machines of that era. Dictaphone technology cut a mechanical groove
into a transparent plastic belt called a DictaBelt. Each Dictaphone machine held
two DictaBelts, and the machine would switch automatically to the second belt to
begin recording before the first belt ended. This resulted in an overlap, and
prevented any interruption in the recording of a conversation.
Electret Microphones
and Sony TC-800B Tape Recorders
To capture in-person conversations, the White House recording system used electret microphones, small condenser microphones which
eliminated the need for a power supply by using a permanently-charged material.
During the 1970s, most electret microphones used a thin metallized Teflon foil
invented by Gerhard Sessler and Jim West of Bell Laboratories. In the Nixon
White House, conversations captured by microphone were recorded on Sony TC-800B
tape recorders. The audio tapes which these devices used consisted of a thin,
plastic base coated with ferric oxide. As the tape passed over the tape head, the
ferric oxide particles were reoriented by the head's magnetic field. After
recording, the tape was covered with magnetized patches of various depths and
directions, which were then translated into sounds.
Resources:
http://en.wikipedia.org/wiki/Watergate_tapes
http://www.washingtonpost.com/wp-srv/onpolitics/watergate/chronology.htm#1973
http://www.paperlessarchives.com/watergate.html
http://millercenter.virginia.edu/index.php/academic/presidentialrecordings/pages/tapes_lbj
http://www.wired.com/wired/archive/10.07/nixon_pr.html
http://www.answers.com/topic/dictabelt
http://www.washingtonpost.com/wp-srv/onpolitics/watergate/chronology.htm
http://www.answers.com/topic/dictation-machine
http://en.wikipedia.org/wiki/Lavalier_microphone
http://en.wikipedia.org/wiki/Electret_microphone
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