The U-47 was the first condenser microphone that could switch between omnidirectional and cardioid patterns. In electro-acoustics, these patterns commonly include omnidirectional, cardioid and hyper-cardioid microphone polar patterns. It included a Shure cardioid microphone headset. The pocket-sized Mikroport incorporated a dynamic moving-coil cartridge microphone with a cardioid pickup pattern. The NHK (Japanese broadcasting company) developed an alternative technique also involving 5 cardioid microphones. These compensate for the bass roll-off of the cardioid microphones and also add expansiveness. Sometimes the woofers have a cardioid characteristic. The signal is radiated in a cardioid pattern. Inverting this polar form shows that a parabola is the inverse of a cardioid. An epicycle with one cusp is a cardioid, two cusps is a nephroid. The picture shows the 4 most common positions of a cardioid and their polar equations. Hence a cardioid is a special pedal curve of a circle. "Remark&colon; "Not every inverse curve of a parabola is a cardioid. The proofs of these statement use in both cases the polar representation of the cardioid.