Question
What is added to an FM speech channel to boost the higher audio frequencies?
Answer Options
- A) A de-emphasis network
- B) A harmonic enhancer
- C) A heterodyne enhancer
- D) A pre-emphasis network
Correct Answer: D
Explanation
In an FM system, the high-frequency components of the modulating signal (voice, music) are generally more susceptible to noise and interference than the low-frequency components. To improve the signal-to-noise ratio of the recovered audio, a form of intentional distortion is introduced at the transmitter, which is then corrected at the receiver.
A pre-emphasis network is a filter circuit added to an \text{FM} speech channel to boost the higher audio frequencies relative to the lower frequencies before modulation. This intentional boosting of the high-frequency components helps them overcome noise introduced in the transmission path. The receiver then uses a complementary de-emphasis circuit to flatten the frequency response back to normal.
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