The AKG C391 B high-performance small-diaphragm condenser microphone is a combination of the Blue Line Series CK91 and the SE300 pre-amplifier. The microphone has a cardioid polar pattern, a low self-noise and very good transient response for a bright and brilliant sound. It also features the ability to quickly interchange its capsule with one of the other capsules of the Blue Line Series, making it an excellent mic for demanding broadcast applications. The C391 B provides a switchable bass roll-off/attenuator with three positions: flat, 75Hz and 10db attenuation.