Using Directional Microphones for Recording Speech

A microphone can pick up sounds from all directions or a specific direction depending on its technical built. This sensitity to sound from one or more directions is called Directionality. Based on this property, there are 3 main types of microphones available -

Omnidirectional Microphones

Unidirectional Microphones

Bidirectional Microphones

Omnidirectional Microphones

These microphones pick up sounds from all directions and are generally used only when there are multiple speakers involved in a recording (as would be in the case of a conference or meetings).

These microphones are not recommended for recording the speech of a single speaker unless you’re recording in a quite room with little or no surrounding noise. This is because omnidirectional microphones capture sounds from all directions and therefore a lot of unwanted sounds such as shifting chairs, doors opening, side conversations, vehicles passing by, etc. can also get recorded.

When using an omnidirectional microphone in an indoors setting, it’s a good idea choose a quiet room and lay down some ground rules for the participants before beginning recording. When outdoors, the microphone should be placed as close to the speaker as possible.

Unidirectional Microphones

These microphones pick up sounds from a single direction – i.e. the direction they’re facing. There are 2 major types of unidirectional microphones -

Shotgun Microphones

Shotgun microphones are best for outdoor recordings because they have a very narrow ‘angle of acceptance’ or ‘pickup pattern’ or simply put, the area from which they pick up sound. This means they can pick up the particular sound they’re directly towards and reject all other surrounding noise to produce a very clear recording.

Long shotgun microphones provide the highest level of directionality and pick up sound from only the person/object that they’re pointed at. This leads to a very high quality of recording and makes them ideal for noisy locations.

The downside of using these microphones is that since they’re very long (and often used with a boom), they normally need a second person to operate. Also, the microphone must consistently be pointed directly towards the speaker – any movement away from the speaker will result in an interruption of the flow of sound to the microphone and thereby impact the recording.

Short shotgun microphones are, well, shorter. Their properties are similar to the long shotgun microphones, the only difference lying in the slightly wider ‘angle of acceptance’ of the short shotgun. They are more portable as well; this makes them the microphones of choice for outdoor recordings that require a degree of mobility – such as interviews conducted on the street.

Shotgun microphones are especially useful when the speaker is not close to the microphone. The more the distance between the speaker and the microphone, the more directional the microphone needs to be.

Cardioid Microphones

Cardioid microphones are the ones used most commonly for speech recording. That’s because they are directional like the shotgun microphones yet offer flexibility in terms of the ‘angle of acceptance’ as well as size and portability.

They pick up sound mainly from the direction that they’re pointed in, some from the far sides of the microphone, and very little from behind the microphone. Since they’re unidirectional, they eliminate a lot of surrounding noise and produce high quality recordings.

Bidirectional Microphones

As the name suggests, these bidirectional microphones pick up sounds from two opposite directions and reject sound from other sides. Also known as figure-of-eight microphones, these microphones are useful for recording two-person interviews where two people are seated on the opposite sides of a table. Bidirectional microphones are not very commonly used because of their limited application.

Some microphones come with multiple options that allow users to switch from let’s say cardioid to omnidirectional mode when required.