A channel is one independent stream of audio samples meant for one speaker position. Mono is a single channel, stereo is two (left and right), 5.1 has six, and an immersive 7.1.4 layout has twelve. Each channel is full-bandwidth except the LFE (.1), which is band-limited for the subwoofer. Channels are the traditional, speaker-bound way to carry surround: the mix is baked for a specific layout, and players downmix when the playback system has fewer speakers. Object-based formats like Dolby Atmos break this model by storing sounds with positional metadata instead, but channels remain the backbone of nearly all delivery today.
