| 摘要 |
A method and apparatus for automatically identifying a program broadcast by a radio station or by a television channel, or recorded on a medium, by adding an inaudible encoded message to the sound signal of the program, the message identifying the broadcasting channel or station, the program, and/or the exact date. In one embodiment the sound signal is transmitted via an analog-to-digital converter to a data processor enabling frequency components to be split up, enabling the energy in some of the frequency components to be altered in a predetermined manner to form an encoded identification message, and with the output from the data processor being connected via a digital-to-analog converter to an audio output for broadcasting or recording the sound signal. In another embodiment, an analog bandpass filter is employed to separate a band of frequencies from the sound signal so that energy in the separated band may be thus altered to encode the sound signal. The invention is particularly applicable to measuring the audiences of programs that are broadcast by radio or television, or that are recorded.
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