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In this master thesis, a voice encryption system was programmed as a real-time
software application. The idea was based on a previous graduation thesis and is
meant to show an example of the possibilities of signal processing for educational
use. The application uses a frequency scrambling technique on an audio signal taken
from the computer microphone input and plays it scrambled back to the speakers, or
other way around to descramble the signal. The basic idea is to use a frequency
channel decomposition through digital signal filtering and down-sampling.
Reassembling these sub-bands in a different order, a scrambled voice signal is the
result. In addition, the scrambling process is embedded into a “software framework”
which allows the use of an audio data stream from and to a sound card through
different APIs so a computer platform real-time application can be accomplished.