Explanation: Double-sideband AM (Amplitude Modulation) signals transmit a carrier wave along with two sidebands, each containing the modulating audio information. The total bandwidth required for a DSB AM signal is twice the highest audio frequency component. For good fidelity voice or music, audio frequencies up to approximately 5 KHz are desirable. Therefore, for a highest audio frequency of 5 KHz, the required bandwidth would be $2 \times 5 \text{ KHz} = 10 \text{ KHz}$. A receiver's IF selectivity of 10 KHz is optimum for faithfully reproducing such AM signals, allowing both sidebands and the carrier to pass while minimizing adjacent interference. Conversely, other modes require much narrower bandwidths: * **SSB voice** typically needs 2.4 to 3 KHz. * **CW** (Morse code) needs a very narrow bandwidth, typically 100 to 500 Hz. * **FSK RTTY** (radioteletype) needs bandwidth from a few hundred Hz up to 2 KHz, depending on shift and baud rate. Using a 10 KHz filter for these narrower modes would introduce excessive noise and interference, degrading reception.