The choice of using frequency modulation (FM) for sound and amplitude modulation (AM) for video in TV broadcasting is primarily due to historical and technical considerations. Let me explain in more detail:
Bandwidth requirements: Sound signals have a much narrower frequency range compared to video signals. By using frequency modulation (FM) for sound, a larger bandwidth can be allocated to accommodate the variations in audio frequencies. This allows for higher fidelity reproduction of sound, capturing a wide range of frequencies. On the other hand, video signals contain a broader range of information, including variations in brightness and color. Amplitude modulation (AM) is used for video to conserve bandwidth and transmit the necessary information effectively.
Noise immunity: FM is generally more resilient to noise and interference compared to AM. This property of FM makes it suitable for carrying audio signals, where preserving the quality and fidelity of the sound is crucial. By using FM, the audio signal can resist noise and maintain its clarity better than if it were modulated using AM. Video signals, on the other hand, are less sensitive to noise interference, and therefore the use of AM for video transmission is acceptable.
Compatibility with existing systems: The choice of FM for sound and AM for video in TV broadcasting systems was made many decades ago when these standards were established. At the time, it was determined that this combination provided a practical and effective solution for transmitting both audio and video signals using the available technology. Changing these standards would have required significant modifications to existing broadcasting infrastructure, which would have been costly and disruptive.
In summary, the use of FM for sound and AM for video in TV broadcasting is a result of the historical development of broadcasting standards, bandwidth requirements, noise immunity considerations, and the compatibility with existing systems. It is important to note that the distinction between sound as intensity (AM) and pictures as intensity (AM) is not the sole factor determining the choice of modulation, but rather a combination of technical and practical considerations.