As any other modems, the design of these "air modems" must account for factors such as the data rate, the error probability and the computational overhead at the receiver. On top of that, these modems must also account for aesthetic and psychoacoustic factors. I will show how to vary certain parameters in standard modulation techniques such as ASK, FSK and Spread-Spectrum to obain communication systems in which the messages are musical and other familiar sounds, rather than modem sounds. Some applications of this technology will be discussed. I will also present the basis of a framework for studying low bit rate communication systems including air modems, bird songs, and human speach.