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Ask the Engineer: Which mic should I use?

Engineer Rob Byers gathers sound in the woods with an enormous microphone.Editor’s note: Rob Byers is a production specialist on NPR’s Editorial Training Team and the author of “Ask the Engineer,” an occasional series of advice about audiocraft and production for AIR. He has worked at Minnesota Public Radio/American Public Media, and as an audio engineer at NPR, and mixes the Criminal podcast for Radiotopia.

And, above all, he’s a wellspring of thoughtful advice about everything that can make audio sound good. This column was published in collaboration with NPR’s Editorial Training Team and is available (with a lot of other excellent advice and resources) at Training.NPR.org.

Without further ado:


Which mic should I use?

Most audio producers and reporters heading into the field will have the basics: a handheld recorder of some kind, a pair of headphones, and one or two microphones.

But which mic should you use?

This is one of the most common questions about field recording and the decision can be confusing. We usually make the choice based on the pickup pattern — the directions from which the mic captures the most sound. But that’s not always the best way! With a little more info we can make a better choice for the job at hand.

Get to know the mics

Different mics allow you to work more effectively in various situations. Understanding the mic you have will allow you to use it more effectively.

Let’s start by exploring those pickup patterns to ensure we understand them.

  • Omnidirectional microphones capture sound from all directions equally. Whether the sound source is behind, in front of, or beside the mic, it’s all the same.
  • Cardioid mics have an upside-down heart-shaped pickup pattern – they capture mostly from the front, not so well from the sides, and reject sound at the rear.
  • The shotgun microphone narrowly focuses on whatever is directly in front of it (even sounds at a distance), rejecting sounds from the sides and the rear.

As Neil Tevault, longtime NPR broadcast recording technician, explains it:

“Pickup patterns are like the inverse of lights (since light shines out but sound radiates towards a mic). An omnidirectional mic is like a bare light bulb, shining on all things equally. A cardioid mic is a like a flashlight, shining forward in a wide but focused pattern and blocking light behind. The shotgun mic is like a laser, narrowly focused on one spot.”

An omnidirectional mic picks up sounds from all directions equally, so you need to hold it close to your subject if there are competing background sounds.  

Which Mic 1 Facebook
Illustration by Chris Kindred, NPR

The shotgun mic focuses wherever it is pointed with a narrow and long beam. It can be really helpful if you can’t get close to your subject.

Which Mic 2 Facebook
Illustration by Chris Kindred, NPR

The cardioid mic is directional and is good at rejecting noise from behind.  However, it can often be quite sensitive to plosives!

Which Mic Web 3 Facebook
Illustration by Chris Kindred, NPR

There’s another factor we need to take into consideration when selecting a microphone. You may have heard the terms dynamic and condenser. These two words describe the inner workings of the microphone. (For the curious, dynamic microphones rely on the movement of a coil around a magnet to turn sound into an audio signal, while condenser microphones use a capacitor.)

These descriptors are used in conjunction with the pickup pattern to give a complete picture of how the microphone operates. It is common for reporters to have one of each – a dynamic omnidirectional mic (like the ElectroVoice RE50N/D-B) and a condenser shotgun (like the Audio Technica AT8035) are frequent choices.

So we’ve got the pickup patterns (omnidirectional, cardioid, and shotgun) and dynamic vs condenser mics. Given all of this, how do you determine which mic to use for field reporting?

Rules of thumb

Here are a few tried-and-true rules of thumb that will achieve reliable results in most reporter-style field situations:

• Omnidirectional microphones experience less wind noise and handle p-pops better than cardioids and shotguns.

If you find yourself outside on a windy day without proper wind protection for your shotgun mic, pull out the omni. An omni will fare much better in gusty winds than a shotgun or cardioid mic.

Windscreen
Proper wind protection for recording with a shotgun outdoors. (NPR image)

• Omnidirectional mics have to be held close to the primary sound – sometimes very close.

Because omni mics pick up sound equally from all directions, any sound in your environment will compete with the primary sound you want to record. Use proximity to your advantage. The closer you are to a sound source, the louder it is, meaning it will be more present in your recording than the sounds from the space around you. If you can’t get close…

• Shotgun microphones have a long reach, which can be helpful when you have to record at a distance.

This is what shotgun mics are known for – their pickup pattern is long and narrow, allowing the mic to focus on distant sounds and reject extraneous sounds from the sides. This can be really helpful in an environment like a “halls of the capitol building”-style scrum when you can’t get close to the voice you need to record or where there is extraneous sound in the environment competing with your source.

• Cardioid microphones can be helpful for handheld, back-and-forth style interviewing but lack the advantages of omnis and shotguns.
Most cardioid mics meant for field use are built to alleviate handling noise. Their pickup pattern can also be used to reject sound from behind the mic. This is nice for on-the-street interviews with one microphone, but it lacks the specific advantages of omnis and shots mentioned above. Alternatively…

• Shotgun mics (and many other condensers) are susceptible to handling noise.

Shotgun mics aren’t built to be held in the hand, but many reporters do it and end up with handling noise on their recordings. The sound of fingers sliding across the surface of the mic or tendons and bones creaking often rears its head at the most inopportune times (like when recording quiet ambience)! Handling noise can be prevented by using a pistol grip with a shock mount, like these common models.

Hand-holding a shotgun mic risks recording handling noise — audible creaks and vibrations transferred from the muscles and bones in your hands to the mic.
Hand-holding a shotgun mic risks recording handling noise — audible creaks and vibrations transferred from the muscles and bones in your hands to the mic.
A pistol grip with a shock mount prevents the sound of handling noise from reaching the microphone.
A pistol grip with a shock mount prevents the sound of handling noise from reaching the microphone.

• Shotgun mics and other condensers often have a helpful high-pass filter.

The high-pass filter removes unwanted rumble and low-frequency noise. That can help alleviate (but not prevent) p-pops, wind noise, handling noise, and level problems with low frequency sounds (like that of a bus zooming by during an on-the-street interview). The filter is usually turned on via a switch on the side of the microphone. Some audio engineers prefer to leave the filter on at all times unless they are recording something where low frequency is important. (Learn more and hear examples of high pass filters  in this article at AIR.)

A high-pass filter on an Audio Technica shotgun.
A high-pass filter on an Audio Technica shotgun.

• Shotgun mics and other condensers often have wonderful presence but can be sensitive to loud sounds.

Condenser mics are known for their present, clear sound and will usually have a crisper sound than a dynamic mic. This sensitivity, however, can mean that they don’t always handle loud sounds well. If you know you will work in a loud area (like in a factory or around loud vehicles) where the voices you want to record will speak very loudly, you may have a hard time managing levels.

• Shotgun mics and other condensers require phantom power, which is an extra drain on battery life.

One of the defining characteristics of condenser microphones is that they require phantom power — a small amount of voltage provided by the recorder. This extra draw on a handheld recorder’s batteries should be considered when choosing a mic. Some models of condensers (like the AT 8035 mentioned previously) can operate on their own battery, sparing those of the recorder. (Just remember to remove the battery from the mic when it’s not in use! They have a habit of corroding and making a mess of the battery compartment.)

This list may feel like a lot to remember, but odds are you already know much of it from experience and intuition! Keep in mind that mics are simply tools and there isn’t a tool that works well in every situation. Each tool has its strengths and weaknesses. Get comfortable with that idea, learn the characteristics outlined above, and you’ll be well-suited to capturing great sound no matter the environment.

Have fun out there!

 

Special thanks to NPR’s Neil Tevault and Serri Graslie (@sgraslie on Twitter) for help with this article.

Where can I learn more?

Gear for starting out field recording

Transom

As I Hear It – Choosing the right microphone