Using a microphone

What are the different types of microphones, and what makes one type more suitable to a particular recording situation?

There are various types of microphone, which can be categorised according to their directionality (ie where they pick up sound from), and the technology used to record the sound (e.g. condenser, dynamic, etc.). We’re not going to go into massive detail on this page – but just give an overview of what you might want to be aware of in choosing and using microphones.

Left: Various mics – from top to bottom: AKG D5 (Dynamic), Milab LSR-2000 (Cardioid Condenser), Shure 16A (Cardioid Condenser), Audio Technica ATM25 (Hypercardioid Dynamic). Right: A Neumann U87 condenser microphone with shock mount

Directionality

All microphones will have a directionality – i.e. where the microphone is ‘focused’ on. Omnidirectional mics are sensitive to sound from all around them; unidirectional mics are focused in one direction; while bidirectional mics are like unidirectional mics but pick up sound from two opposite directions in one plane (like, from directly in front and directly behind). Omnidrectional mics are good for situations where the sound source is moving around.

Transducer technology

Dynamic microphones

Dynamic microphones are robust and can withstand a wide range of sounds – making them well-suited to situations like recording live music. Dynamic microphones can be either moving coil microphones or ribbon microphones. Moving coil microphones are the most durable type of microphone and can often withstand high sound pressure levels – for recording, say, loud music. Ribbon microphones are often much more fragile. Dynamic microphones do not need phantom power to operate. In fact, phantom power will break most ribbon microphones.

Condenser (capacitor) microphones

Condenser (or capacitor) microphones require power – typically 48 V, called phantom power. Vibrations in the air cause the capacitance to change, converting vibrational energy into electrical modulation. Condenser microphones are generally more sensitive than dynamic microphones – making them better suited to subtle sounds, including vocals.

Diaphragm size

The size of the microphone’s diaphragm has an effect on its frequency response. Generally microphones with smaller diaphragms such as pencil condenser microphones pick up higher frequencies well. Larger diaphragm microphones can pickup lower frequencies better.

Choosing a mic

So, as you can see, there are a range of options when choosing a microphone. If you are recording a range of different situations (live music, spoken interviews, on-the-move recording), and you have a budget, it makes sense to buy a range of microphones and use the most appropriate one for each job. If your budget is more limited, think about all the different things you need to use the mic for and try to find something which will do a reasonable job of as many of them as possible.

For vocalists a simple cardioid dynamic mic is a good starting point. For interview work, go for a mono mic. You can use a stereo mic for recording atmospheric sound/wildtrack and actuality, but if you want to record voices in stereo, you need to think carefully about how many mics you will need and where you’re going to place them. For video makers, a useful option is a condenser mic with selectable directionality, so you can change between cardioid and hypercardioid. If you can afford three mics, consider a hand-held dynamic, a shotgun condenser, and a lapel mic.

Cardioid mics

These mics are directional, and they’re more sensitive to sounds coming from one particular direction, often the front of the mic. Cardioid mics are good for favouring one sound while rejecting another from a different direction, but you need to know what you’re doing. If you’re just starting out, take an omni mic. It’s the most flexible, and cardioid mics need more careful use.

Omni-directional mics

An omni is an omni-directional mic, meaning it picks up sounds from all directions. It’s a good general purpose mic, particularly useful for interview work, but also good for recording atmos and actuality. Many a package has been made using only an omni mic.

Clip mics

Often used in TV as they’re less obtrusive. Clip mics are usually small omni mics. There are a variety of sizes, but they’re all small enough to clip on to clothing. Where you clip the mic is very important – too far from the voice and it will sound distant; too close to the chin and it can sound muffled. You need to consider your interviewee’s clothing – certain fabric will rustle, which will degrade the recording. And if you clip a mic to a man’s shirt, make sure that his tie doesn’t fall across the mic. Clip mics have their uses but hand-held mics will generally give you a better sound.

The mic and its accessories

As well as your mic, you will need:

A windshield: often a foam cap which covers the business end of the mic. The windshield minimises wind noise on location.

A lead: connects your mic to your portable recorder. Before you set off, check you’ve got the correct lead with the right connections for the portable recorder you’re using.

Batteries: some mics need to be powered by a small battery. Check before you leave and replace if you’re in any doubt about how old the battery is. If you’re going to be spending a long time on location, take spare batteries.

Tip: For emergency waterproofing of your mic (if you really have to record that location interview in the pouring rain) slip a condom over your mic, under the windshield!

Headphones: Remember… a mic will pick up noises that you may not hear – or that your brain tends to filter out. So always wear headphones when you’re recording.

Sound issues

Handling

If your mic is likely to be subjected to any sort of handling noise or vibration, you will need a mic which will help prevent this noise from being picked up. High quality hand-held mics usually attempt to isolate the diaphragm from vibrations using foam padding, suspension, or some other method. Low quality mics tend to transfer vibrations from the casing right into the diaphragm, resulting in a terrible noise.

Placing the mic

It’s very important to get the placing of the mic right – to get the right distance between mic and subject. In general, place the microphone as close as practical to the subject without getting so close that you introduce unwanted effects. The aim is to achieve a good balance between the subject sound and the ambient noise. You will generally want the subject sound to be the clear focus, filled out with a moderate or low level of ambient noise. The desired balance will vary depending on the situation and the required effect. For example, interviews usually work best with very low ambient noise. However if you want to point out to your audience that the surroundings are very noisy you could hold the mic slightly further away from the subject. It is possible to get too close – e.g., if a vocal mic is to close to the speaker’s mouth, the audio may be unnaturally bassy (boomy, excessive low frequencies), and you may get ‘popping’ and other unpleasant noises. Consider the following problems and solutions… Problem 1: Recording an interview in a noisy environment (e.g. busy street, sports event, press conference) and trying to get a good level on the speaker/interviewee above the background noise Solution 1: Position the mic closer than usual, but be very careful to avoid popping. Set your level with the mic in this position. Problem 2: Recording both a quiet and loud voice – and getting the balance of levels right Solution 2: So that you’re not constantly fiddling with the levels, set your level against one of the voices and then position the mic so that it is nearer to the quiet voice and further away from the loud voice.

Large and open spaces

If you are recording in a large room, say a hall, this can cause echos and reverberations. You can improve sound quality by avoiding recording in the middle of the room, moving to one side. (However, not too close to the wall, as this may pick up too much reflected sound.) If you can muffle echoes by closing curtains, that can also help the sound quality.

Things to note

Be aware of what type of mic you’re using. In particular, you should know about its directional characteristics. Make sure you do a sound check yourself, well before the interview. Position yourself and the microphone, and speak exactly as you intend to during the interview. If the mic has an on/off switch, keep an eye on it. If the mic is battery-powered, make sure you turn it off when you’ve finished. Hold the microphone firmly. Remember that the mic will pick up any handling noise so be careful not to move your hand around on the mic casing, or bump the mic into anything. If you’re exposed to the wind, try and give the mic some shelter. Hold the mic at a constant distance and angle from your mouth (or your subject’s mouth). Around 15-20cm from the mouth should be fine. Any more than this, and not only will the voice become weak, but other noises will become more prominent. Any closer than this, and you’ll get various unpleasant sound effects (such as “popping”). Always direct the mic towards the person who’s talking. You can also use mic-pointing to direct your subjects. When you point it at yourself, you’re talking. When you point it at the subject, you’re saying “Now it’s your turn to talk”. If you have more than one subject, you can use the mic to point toward the person you want to speak. Never give the mic away during an interview. It’s not uncommon for a subject to want to hold the mic, but don’t let them. It creates all sort of problems and it’s just not worth it.