What is the primary characteristic of a cardioid microphone?

The primary characteristic of a cardioid microphone is indeed its heart-shaped pick-up pattern. This design allows the microphone to capture sound primarily from the front while reducing sound from the sides and rear. This directional characteristic makes cardioid microphones particularly effective for live performances, recording vocals, or isolating a particular sound source, as they can minimize background noise and feedback from other instruments or sounds in the environment.

In contrast, other microphones might capture sound more evenly from multiple directions, which can be less desirable in situations where you want to focus on a specific sound source. The unique shape of the cardioid pattern allows for greater control over audio input, which is one of the reasons it's a popular choice in various audio settings.

The concept of requiring an external power source does not apply universally to cardioid microphones, as many dynamic cardioid microphones operate without needing phantom power. Additionally, the design and function of cardioid microphones are not restricted to indoor use, as they can also be effective in outdoor environments, making their flexibility an important characteristic.