The Sennheiser MD 421 was released in 1960 to much acclaim, with a very tight cardioid polar pattern that borders on "supercardioid" at many frequencies and a clear, present sound that was far superior to most dynamic mics of the era.

The MD 421-HL model features a 3-pin DIN connector, dual impedance and unbalanced operation. The HL model does have the M-S (music-to-speech) high-pass filter switch, though it only has two positions.