In what scenario would you use a 'line-level' audio signal?

Using a 'line-level' audio signal is most applicable when sending audio signals from one device to another. Line-level signals are standardized levels of audio voltage that are typically used for interconnecting audio devices such as mixers, amplifiers, and effects processors. These signals are much stronger than microphone-level signals, which require amplification, and are less prone to noise over longer cables.

In contrast, when inputting sound to a recording device, that scenario might involve the use of various signal levels including microphone or instrument levels depending on the setup and desired quality. Connecting microphones directly to amplifiers involves microphone-level signals, which are lower in voltage and require special preamplification. Lastly, transmitting audio wirelessly does not specifically align with line-level signals; wireless systems utilize modulation techniques to send audio over the air and can transmit a range of audio signal levels. Thus, the correct application of line-level audio is primarily associated with inter-device connections.