Now that the students have seen representations of music and speech on the computer, we move into the issue of how to communicate this information. We present two lectures. The first is on AM/FM modulation, and borrows on the students experience tuning a radio station and selecting a television channel. We do not perform any noise analysis, but simply demonstrate how to communicate information carried by a modulating waveform. In the laboratory, the students leverage their previous laboratories on real-time tone generation to build a system that generates touch tones, i.e., a dual-tone modulated-frequency (DTMF) system [9][3]. We also have them recognize the presence of a '1' digit in real time.
The second lecture is on binary frequency shift keying (BFSK) and its use in digital modems. We introduce the issue of matched filtering for this binary case. In the laboratory, the students reuse the DTMF codec from the previous laboratory to build a simple BFSK modem.