When should you use a cardioid microphone? This is a question I get asked a lot. There are a few basic guidelines I lay out for my trainees and you can do the same. When should you use a cardioid microphone?
What is a cardioid microphone? It is also sometimes referred to as a “C” microphone or a “D” microphone. Essentially it is a microphone that takes sound waves and converts them to electrical signals. This makes the signal strong enough to use with an amplifier but not so strong as to destroy the signal or produce what is commonly called “shatter” effects.
What does this mean? It means your microphone will take very strong sound waves, and if done incorrectly, will produce a signal that is directional. Basically it will give you directional audio. If you send the signal in only one direction, it will be very “thin” and not very directional. However, if you send the signal in both directions, you will get a much stronger signal which will be much more directional and will make the audio much more listenable.
How is this useful? Well, let’s say you are recording vocals. In order to capture the voices from each source, you would need to record with two microphones, each one with its own cardioid-type patterns. Now imagine trying to mix the two mics during the same session, this would be impossible without using an external mixer. With an external mixer, you can feed both microphones different signal sources and use polar response patterns to get the desired result.
Another advantage of having a cardioid-type microphone is that the front diaphragm acts as a cardioid and acts to dampen the back noise. The rear null point has a lot to do with the sound level as well and needs to be carefully set up. The reason for the rear null point is so that the sound can be controlled by the front diaphragm better and so that the sound from the rear microphone can be amplified without losing the quality of the sound from the front microphones.
How is this useful? Well, in conjunction with the above mentioned null points, the on-axis response pattern (or cardioid) is used to “tune” the sound and isolate the frequencies that will produce the best sound quality. Basically the on-axis response pattern captures the highest frequency that can be amplified without losing any of the other frequencies. As you get into more advanced audio recording techniques, such as mastering, you’ll find that using on-axis responses is more beneficial. It’s also used for tracking since tracking with cardioid microphones is much easier than tracking with anything else.