Directional microphones are designed to pick up sound primarily from one direction and suppress sounds coming from other directions. The most common type is the cardioid microphone, whose pickup characteristic when graphically represented resembles the shape of a heart. This means that it is most sensitive to sound coming directly from the front, while it picks up sounds from the sides with less intensity and almost completely ignores sounds coming from behind. This characteristic is useful in situations where it is necessary to isolate a particular sound source from ambient noise. For example, when recording a vocal or podcast, the microphone focuses on the speaker's voice and minimizes unwanted room noises such as echoes or computer noise. During live performances on stage, the cardioid characteristic helps prevent feedback, which is an annoying squeak caused by the microphone picking itself up from the speakers. Because the back of the microphone is insensitive, the eavesdropper can be pointed at the performer without their sound leaking back into the microphone.