Which sound mix utilizes only a single channel for audio?

The correct response is rooted in the definition and characteristics of audio mixing techniques. Mono, short for monophonic sound, involves the use of a single audio channel. This means that all audio playback, regardless of the source material, is directed through one channel, providing a uniform sound experience that does not vary by speaker placement. In contrast, stereo involves a dual-channel setup, which allows for a more rich listening experience by panning sounds across the left and right speakers. Surround sound expands on this concept even further, incorporating multiple channels for an immersive audio environment, typically involving at least five channels. Ambisonic sound goes further to provide a three-dimensional audio experience, capturing sound from all directions with multiple channels. Thus, mono distinguishes itself as the sole method that relies solely on one channel for its sound output, making it the correct answer for this question.