Which of the following terms describes an interface that allows multiple audio sources to be mixed together?

An audio mixer is an essential device in the audio production process, specifically designed to combine multiple audio sources into a single output. It provides the necessary controls to adjust levels, balances, and effects for each audio input, allowing for a cohesive sound mix. This functionality is crucial in various contexts, such as live sound reinforcement, studio recording, and broadcasting.

On the other hand, an audio interface mainly serves as a bridge between audio equipment and a computer, converting analog signals to digital and vice versa, but it does not inherently mix audio sources. An audio decoder converts digital audio signals into analog form or processes audio formats, focusing on signal interpretation rather than mixing multiple sources. An audio splitter sends a single audio signal to multiple output destinations without mixing, thereby preserving the original source rather than combining various inputs.

Therefore, the term that best describes an interface for mixing multiple audio sources together is indeed the audio mixer.