Companding

A modulation technique in which the carrier frequency is shifted by an amount proportional to the value of the modulating signal. The amplitude of the carrier signal remains constant. The information signal causes the carrier signal to increase or decrease its frequency based on the waveform of the information signal.
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A method of testing or defeating the robustness of a watermark. This attack applies “jitter” to a cover by splitting the file into a large number of samples, the deletes or duplicates one of the samples and puts the pieces back together. At this point the location of the embedded bytes cannot be found. This technique is nearly imperceptable when used on audio and video files.
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A measurement of the number of wave oscillations within a specific time identified using the unit Hertz (Hz), or oscillations per second. Radio waves have a frequency between 3 Hz and 300 GHz. The rate at which an electromagnetic waveform alternates, usually measured in Hertz.
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A piece of hardware used to connect computers (or certain other network devices) together via a serial cable (usually a telephone line). When data is sent from your computer, the modem takes the digital data and converts it to an analog signal (the modulator portion). When you receive data into your computer via modem, the modem takes the analog signal and converts it to a digital signal that your computer will understand (the demodulator portion).
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The most common and most important method that a telephone system in North America can use to sample a voice signal and convert that sample into an equivalent digital code. PCM is a digital modulation method that encodes a pulse amplitude modulated signal into a PCM signal.
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