On a microphone’s spec sheet you will see terms such as “unidirectional” and “omnidirectional”. These describe the “polar pattern”, which shows from which directions a microphone picks up sound most easily. In home recording and cover-song recording, most microphones are unidirectional. Knowing why, and what the other types are good for, makes choosing and placing a microphone less confusing. This article uses official materials from the microphone maker Shure to sort out the differences between polar patterns and how they relate to the proximity effect.
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Bottom line: for home vocal recording, start by thinking “unidirectional”
- A polar pattern describes “from which directions a microphone picks up sound most easily”. Shure calls a diagram that shows, angle by angle, whether the microphone picks up sound from the front or from other directions more strongly a “polar pattern”.
- Shure describes the commonly used patterns in three groups: omnidirectional, unidirectional and bidirectional.
- For recording cover-song vocals, a unidirectional pattern (Shure describes cardioid as the common one), which picks up the voice in front and picks up less from behind, looks like a good fit.
- The proximity effect (the bass getting stronger the closer you get to the microphone) occurs, in Shure’s explanation, with unidirectional microphones. It is said to be less likely with omnidirectional ones.
What a polar pattern is
Shure explains a polar pattern as “how sensitivity changes depending on the direction or angle of the sound reaching the microphone.” A diagram that goes all the way around the microphone, 360 degrees, and draws how much the sensitivity changes at each angle is the polar pattern.
The diagram is simple to read. The front of the microphone is 0 degrees. If the line bulges far outward at 0 degrees, the microphone picks up sound from the front well. If the line dips inward at 180 degrees (directly behind), it means sound from behind is picked up less.
What matters here is that a polar pattern is not a “function that removes noise” but a property of “which directions are picked up relatively quieter”. Even if the sensitivity at the back is low, sound coming in from the front is picked up, noise included.
The three basic patterns and how each picks up sound
Omnidirectional: picks up all directions equally
Shure explains that an omnidirectional microphone “responds equally from any angle, with a pickup range of the full 360 degrees.” Drawn as a polar pattern, it is almost a circle.
- Strengths: Shure explains that omnidirectional gives a natural, open sound and suits recording acoustic instruments such as an acoustic guitar.
- Weaknesses: It also picks up a lot of room sound (ambience). Shure words it as something that can be an attraction if the room sounds good. It also explains that at live venues it easily picks up the sound of the speakers, and feedback (a howling sound) is more likely.
- How to adjust: Shure explains that the balance between the direct sound and the room sound can be set by changing the distance between the microphone and the instrument.
When recording at home, room reverberation and air conditioner noise are likely to come in as they are, so an omnidirectional microphone may be a candidate when you have a quiet environment with a well-controlled room sound.
Unidirectional: picks up mainly the front
A unidirectional pattern picks up sound from one particular direction the most. Shure explains that the most common is the “cardioid”, which looks heart-shaped. Sensitivity is highest at the front (0 degrees) and lowest directly behind (180 degrees).
- Shure explains that the ambient sound a cardioid picks up is about one third of that of an omnidirectional one.
- The practical pickup angle (effective range) is given as 131 degrees, and it is described as able to handle one or two singers and to keep picking up a singer who moves a little.
- It also explains that at live shows it is more resistant to feedback than omnidirectional.
In other words, by pointing it at the voice, you can keep down the room sound and the sound from behind while recording mainly the voice. The fact that most vocal microphones for home recording are cardioid is probably because this property is easy to use.
Relatives of unidirectional: supercardioid and hypercardioid
Shure introduces supercardioid and hypercardioid as types that pick up an even narrower area in front than cardioid. The pickup angle is 115 degrees for supercardioid and 105 degrees for hypercardioid. They pick up even less of the surrounding sound, but sensitivity directly behind does not drop completely, and the direction that picks up least shifts to a diagonal toward the rear.
For that reason Shure advises taking care where you place stage monitor speakers. However, this is mainly a live-sound matter. If you simply record alone at home, cardioid is unlikely to give you trouble to begin with.
Bidirectional (figure-8): picks up front and back, not the sides
A bidirectional pattern has high sensitivity at both the front (0 degrees) and directly behind (180 degrees), and lowest sensitivity at the sides. Because the shape resembles the number “8”, it is also called “figure-8”.
- Shure explains that it can be used to record two sources at the same time, such as two singers facing each other.
- The pickup angle is narrow, and if there is no other source directly behind the microphone, it can also be used to isolate a single voice.
- However, Shure writes that “in many cases only one side is used.”
In home recording for a single singer, there may not be many situations that call for bidirectional. Recording a duet with one microphone is one possible case.
How polar patterns relate to the proximity effect
The proximity effect is the phenomenon where the closer you bring the microphone to your mouth, the stronger the bass you record. Shure explains that with a unidirectional microphone, the bass increases the closer the distance to the source. It also advises that when you get closer than 1 foot (about 30 centimeters), you should be careful about the proximity effect and cut the low end if needed.
- Unidirectional (cardioid and so on): The bass increases as you get closer. It can add warmth to the voice, but if you get too close it can sound muffled. How to think about distance is explained in “Microphone distance and pop filter use for cover-song recording“.
- Omnidirectional: Shure gives an example that with an omnidirectional microphone you can avoid the proximity effect and also reduce pop noise (the blast of air on “p” sounds).
- Subcardioid: A pattern between omnidirectional and cardioid, with a very small proximity effect, Shure explains.
What we can say here is that how easily the proximity effect appears changes with the type of polar pattern. How large or small the change in sound is when you vary the microphone distance is also considered to be related to the polar pattern.
How to choose for home vocal recording
From here on, these are ways to think about where to use each pattern, based on the official explanations. How it actually sounds changes with the microphone model and the room.
- Recording one vocalist: Unidirectional (cardioid) is the basic choice. It picks up mainly the voice and reduces the room sound behind you.
- Worried about room reverberation: Choose cardioid and sing facing the front. An omnidirectional microphone also picks up a lot of room sound, so it may get in more if the room is not well controlled.
- Recording an acoustic instrument naturally: As Shure treats omnidirectional as suited to acoustic instruments, it is a candidate in a quiet room.
- Two or more people on one microphone: Shure’s materials describe bidirectional for two people facing each other, and omnidirectional for several people gathered around.
- Microphones with pattern switching: Shure describes a multi-pattern microphone, whose pattern can be switched, as “two microphones in one”. If you want to try various patterns with a single microphone, choosing a switchable one is an approach.
The difference between condenser and dynamic microphones is explained in “Dynamic vs condenser microphones“, and if you want to compare microphones, you can check “Microphone comparison list“.
Cautions about microphone direction and placement
- Do not point it the wrong way: A unidirectional microphone has a pickup face (the front). Which face is the front differs from microphone to microphone, so check the instruction manual.
- Do not put a source directly behind it: With supercardioid, hypercardioid and bidirectional, some sensitivity remains directly behind.
- Angling it changes the sound: Shure explains that “off-axis (away from the front), the frequency response is not consistent, and especially the highs change and can sound unnatural.” Recording a voice from the front is the basic approach.
- Adjust the sound with distance: Distance changes the balance between the direct sound and the room sound.
Frequently asked questions
Q. With a unidirectional microphone, does sound from behind disappear completely?
It does not disappear completely. A unidirectional microphone only “picks up sound from behind less”; it does not pick up none at all. Shure also explains that the ambient sound a cardioid picks up is about one third of an omnidirectional one, and does not say it is zero.
Q. Can I not use an omnidirectional microphone for cover-song recording?
It is not that you cannot. But since it also picks up a lot of room sound, it suits a place where the room sound is well controlled. It is safest to start by thinking of unidirectional as the basic choice.
Q. Is the proximity effect a bad thing?
Not necessarily. It can make a voice sound warmer. Shure advises adjusting the low end when you use the microphone close. Decide how to deal with it based on whether you want to get close to the microphone.
Q. Where can I find the polar pattern of a USB microphone?
It is written in the product’s spec sheet or instruction manual. It may be written in English terms such as “Cardioid”, “Omnidirectional” or “Bidirectional”. It is reassuring to check before you choose.
Summary
A polar pattern describes “from which directions a microphone picks up sound”. Omnidirectional picks up all directions, unidirectional picks up mainly the front, and bidirectional picks up the front and back. For home vocal recording, treat unidirectional, which picks up the voice in front, as the basic choice, and remembering that it brings the proximity effect makes it easier to adjust distance. When you choose a microphone, also look at the polar pattern entry on the spec sheet.
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