Spatial pickup geometry of a mic — cardioid, omnidirectional, figure-8. Defines what gets recorded from where. Critical for rejecting unwanted sound.
Every microphone does not hear equally in all directions. The polar pattern describes how sensitive the mic is to different directions in space — and this is one of the first decisions on set before you pound the poles into the ground. You don't choose the best microphone, but the best microphone with the right polar pattern for the situation.
The most common patterns are cardioid — heart-shaped, picks up from the front, strongly rejects the rear —, supercardioid with even tighter pickup and narrow null points, and omnidirectional, which is equally sensitive everywhere. Then there's the figure-8, which picks up from the front and rear but completely ignores the sides. With high-quality wireless and lavalier microphones, you'll also find hypercardioid patterns — even more precise than supercardioid, but also more temperamental with handling noise. Additionally, there's cardioid gradient — a gradual transition pattern between cardioid and supercardioid.
In practice, this means: If you're shooting in a noisy restaurant with only one actor, you need an aggressive supercardioid or hypercardioid on a boom, capturing the dialogue and relatively ignoring the background chorus. On a quiet location with an ambience focus, you'd use the omnidirectional because you want to capture the spatial atmosphere completely — all microphones in the scenario deliver the same polar pattern, and your mix will be consistent. For a two-person dialogue shot on a couch, a cardioid might suffice if you have clean positioning; however, if you're trying to reject the speaker box behind the camera, you'd switch to a supercardioid or position the microphone capsule differently.
A common mistake: choosing the polar pattern and then ignoring that it is frequency-dependent — at low frequencies, even cardioids become wider. A 60 Hz hum from behind will therefore penetrate even the best cardioid. That's why you combine polar pattern with positioning and with high-pass filters. The best pattern won't help you if the microphone is incorrectly positioned or misaligned. And remember: every pattern has its sweet spot — the distance and angle at which it works optimally.