What happens when you plug a mic into a line or instrument input? - YouTube
resistors - Line level to microphone level to record - Electrical Engineering Stack Exchange
Whirlwind PB12 Passive Press Box with 1 Line in to 12 Mic out
Amazon.com: LZSIG Mini Audio Mixer,Stereo Line Mixer for Sub-Mixing,Ultra Low-Noise,4-Channel,Microphone Independent Control, 1/4" & 1/8" TRS Output and Input, for Guitars,Bass,Keyboards or Stage Mixer Extension : Musical Instruments
MIC LEVEL vs LINE LEVEL: Audio Levels Explained – Audio University