Explanation: When designing an audio filter, the fundamental goal is to select or reject specific audio frequencies. An audio filter's ability to pass a certain range of frequencies while attenuating others is defined by its **bandpass characteristics**. This includes parameters like the center frequency, bandwidth, and the steepness of the roll-off. Op-amps are ideal for active audio filters because they provide gain and can create precise frequency responses using only resistors and capacitors, eliminating the need for bulky inductors. In amateur radio, audio filters are critical for improving signal intelligibility, especially for CW (narrow filters for Morse code) and SSB (filters to pass voice frequencies, typically 300-3000 Hz), by reducing noise and interference outside the desired passband. The other options are incorrect: * **B) Desired current gain:** While an op-amp provides gain, the *primary parameter* defining a filter is its frequency response, not specifically current gain. The gain is used to implement the desired frequency characteristics. * **C) Temperature coefficient:** This describes how a component's value changes with temperature. While important for circuit stability, it doesn't define the filter's fundamental frequency-selective function. * **D) Output-offset overshoot:** This relates to transient response or DC error characteristics of the op-amp itself, not the filter's primary function of frequency selection.