While sound waves in their physical form are three-dimensional, when we refer to sound waves in the context of audio transmission, we often simplify their representation to two dimensions: frequency and amplitude. This simplification is known as the frequency modulation (FM) technique used in radio broadcasting.
In FM radio, the audio signal (which contains information about the sound waves) is modulated onto a carrier wave by varying its frequency. The amplitude of the carrier wave remains constant, and only the frequency is modified according to the audio signal. This modulation process is achieved by changing the instantaneous frequency of the carrier wave in proportion to the variations in the audio signal.
To understand how the sound is accurately transmitted with FM, we need to consider the concept of modulation index. The modulation index determines the extent to which the frequency of the carrier wave varies. By controlling the modulation index, it is possible to accurately reproduce the variations in the audio signal.
When the audio signal has a low amplitude or volume, the frequency deviation of the carrier wave is small, while a high amplitude audio signal results in a larger frequency deviation. This modulation of the carrier wave allows the audio signal to be encoded in the frequency variations of the wave.
At the receiving end, the FM radio receiver demodulates the carrier wave, extracting the original audio signal from the frequency-modulated wave. The receiver detects and decodes the changes in frequency to reconstruct the original sound wave, including both its frequency (pitch) and amplitude (volume) variations.
In summary, although sound waves themselves are three-dimensional, FM radio simplifies their representation to two dimensions (frequency and amplitude) for transmission purposes. The frequency modulation technique encodes the audio signal by varying the carrier wave's frequency, while the amplitude remains constant. This modulation and subsequent demodulation process allows for accurate transmission and reproduction of the original sound wave.