The BK-5B is a vintage ribbon microphone with a uni-directional (cardioid) pickup pattern, which is uncommon for a ribbon microphone. Like most vintage RCA microphone it also has a voice switch that changes the low end response of the microphone. “M” is full range while “V1” and “V2” are low-cut filters. Compared to most ribbon microphones it has a strong midrange response which makes it a popular choice on guitar amps.