The Yamaha MG 12/4 is a compact 12-channel analog mixing console designed to combine, process, and route multiple audio signals (such as microphones, instruments, and playback devices) into balanced stereo or group outputs for live sound, small bands, and home recording. 

Key Functions & What It Does

• Signal Mixing: Takes up to 12 total audio inputs (typically featuring mono microphone/line channels and stereo line channels) and blends them into a unified main stereo mix.
• Preamplification: Uses built-in low-noise microphone preamps to boost quiet mic signals to line level, complete with switchable +48V phantom power for condenser microphones. 
• Tone Shaping (EQ): Applies a 3-band channel equalizer (high, mid, low frequencies) and high-pass filters to clean up or sculpt the sound of individual channels.
• Dynamics Control: Features built-in compression on select mono channels to smooth out uneven vocal or instrument volumes.
• Routing & Buses: Provides 4 total buses (main stereo bus and a stereo group/subgroup bus) along with auxiliary (AUX) sends to route audio to external effects processors or stage monitor speakers.
• Outputs: Sends the final combined audio via balanced XLR or 1/4-inch main outputs, group outputs, and a dedicated headphone/monitor jack.

Presented in excellent condition with power lead and AC power adaptor in original box.