What minimum number of audio channels must a digital bitstream contain to qualify as 5.1?

To qualify as a 5.1 audio system, a digital bitstream must contain a minimum of six audio channels. This configuration typically includes five full-range channels for the main audio tracks—left, center, right, left surround, and right surround—plus one low-frequency effects (subwoofer) channel, which is designated as the ".1" in 5.1.

Each of these channels plays a specific role in delivering a comprehensive surround sound experience, where stereo channels (two channels) are inadequate for creating the immersive effect provided by the multiple dedicated channels. Thus, the requirement of six channels is what distinguishes 5.1 audio systems from simpler audio formats.