What device is used by a radio station to select and control the level of audio sources to be put on the air?

The device used by a radio station to select and control the level of audio sources to be put on the air is the audio mixing console. This tool is fundamental in managing multiple audio inputs—from microphones to music players—and allows an operator to blend these sources together into a cohesive output for broadcast.

An audio mixing console provides essential features such as volume control, panning, and equalization for each audio channel, enabling the operator to achieve the desired sound quality and balance. It ensures that the final output is mixed properly before being transmitted, which is crucial for maintaining professionalism and clarity in radio broadcasts.

While the other options play important roles in audio processing, they do not encompass the full range of functions that an audio mixing console provides. A microphone preamp primarily amplifies the signal from a microphone, an equalizer adjusts frequency levels for tone shaping, and an audio compressor controls the dynamic range of audio signals. However, none of these devices combine the selection and level control functionalities that are essential for getting audio on the air as effectively as an audio mixing console.