Question

The audio signal:
(A) can be sent directly over the air for large distance
(B) cannot be sent directly over the air for large distance
(C) possess very high frequency
(D) none of the above

Answer 1

Hint: An audio signal is a representation of sound, typically using either a level of electrical voltage for analogue signals or a series of binary numbers for digital signals. Physical waveforms of sound are converted into electrical representations of these waveforms using transducers, such as a microphone, before being transmitted using a telephone line or radio.

Complete step by step answer:
Audio signals have frequencies in the audio frequency range of roughly \[20Hz\] to \[20,000Hz\]. These values correspond to the lower and upper limits of human hearing. These frequencies, although may seem high in truth, high frequency ranges from \[3MHz\] to \[30MHz\].
Coming to the transmission part of the question, signals must be amplified for long-distance transmissions but energy gets lost due to attenuation. The range of transmission depends upon the height of the transmitting antenna. To make long-distance transmissions, the height of the antenna needed is very large and impracticable. Also, since the frequency of the signal isn’t very high, over long-distance transmission, the energy of the signal is considerably reduced causing the signal to become distorted or indiscernible. Attenuation depends upon a lot of physical, external and internal factors.
All the above reasons establish that an audio signal cannot be sent directly over the air for large distances. Hence, option (B) is the correct answer.

Note: We have seen that air isn’t the appropriate medium for long-distance audio transmissions, so how do we do it? How do we transmit audio signals over large distances? There are two possible ways for long-distance audio transmissions. We can either modulate the audio signals’ frequency to the order of a few megahertz or we can use shielded cables with transformers at the sender and the receiver’s end.