What are the opposite words for two-channel?

The antonym for "two-channel" would be "mono" as it denotes a single channel or sound source. It is also referred to as monaural or monophonic, opposite to stereo or binaural sound systems. This means that there is only one audio input and output for the audio playback, unlike the two-channel system that has two separate channels for left and right audio streams. The mono sound system is commonly used in older audio devices or retro music systems, while the modern audio systems prefer a multi-channel or surround sound system that offers a more immersive listening experience.