Fourier series of a periodic rectangular pulse has a continuous sepctrum

for a signal to be reproduced without distortion alll harmonics should be present

The SI unit of audio frequency is the hertz (Hz). It is the property of sound that most determines pitch. The generally accepted standard range of audible frequencies is20 to 20,000 Hz, although the range of frequencies individuals hear is greatly influenced by environmental factors.

Coaxial cables have a bandwidth in the range of 750 MHz