What are sources connected to an audio mixing device so they can be broadcast or recorded?

The correct choice relates to the role of an input channel in audio mixing devices. An input channel is designed specifically to accept various audio sources—such as microphones, instruments, or other audio playback devices—allowing these signals to be processed, mixed, and subsequently either recorded or broadcasted.

By having multiple input channels, audio mixers can handle a range of audio feeds, each adjustable for level, tone, and effects before finally sending the collective sound to the output, whether that’s for recording or live transmission. Using various input channels allows sound engineers to create a balanced mix from different sources, which is crucial in both broadcasting and recording environments, ensuring clarity and control over the final audio output.

The other options do not correctly describe the connection of audio sources to mixing devices. An output channel refers to where the mixed audio signal is sent out, a signal path is more about the route taken by audio from input to output rather than the channel itself, and a transmission line typically pertains to the physical medium through which signals travel rather than the mixing devices' input mechanics.