Choosing and using mics for video production

As more and more individuals and organisations share their stories and marketing messages via video, it is becoming increasingly important to ensure the quality of your video production is as high as possible, in order to compete in a crowded marketplace. While a great deal of emphasis is often placed upon the visual quality of our video content, the crucial partner to this, the audio, is frequently neglected. However, just as a blurred or badly lit image will degrade a viewer’s experience, distorted, confused, or incongruous sounding audio will do the same; in fact, arguably more so! If we want our marketing videos to engage viewers and leave them with the best impression of our brand, it’s important to pay attention to offering the best audio possible. Fortunately, there are some very simple steps we can take and surprisingly affordable purchasing options available, to bring our sound to the next level, well beyond anything we can hope to achieve with a built-in camera mic or mobile device mic. This article looks at a range of microphone options, discussing how and when they’re best used to deliver the most engaging audio possible for your videos.

Location, location, location

Before we even start to consider equipment, it’s a good idea to discuss what is often the real elephant in the room when it comes to audio recording, and that is the space you’re recording in itself. In just the same way that it’s always desirable to shoot video in an environment where you can control lighting as much as possible, it’s just as desirable to capture audio in an environment where you can pin down the sound! Difficult environments for audio, i.e. spaces with hard flat surfaces that bounce sound around, result in confused or unnatural sounding audio. If you work in a room with unfortunate acoustics, try hanging some drapes or blankets in front of the walls, put a rug on the floor and close the curtains. Equally, environments where unwanted sounds are being generated, such as noisy air-con, traffic noise, buzzing refrigerators, etc, are rarely a good place to start. If you can, chose a space to shoot where these things are less of an issue, if you can’t, take steps to control them such as closing windows, turning off the ventilation system and the fridge for a while, and so on. 

Of course, there are numerous products available for helping to treat room acoustics, but these can prove expensive and tend to be installation focussed (i.e. for permanent studio use), rather than portable items. Acoustic foam, for example, takes audio (kinetic) energy and turns this into thermal energy, and is very effective at reducing audio reflections in a room but is both costly and unsightly and definitely, won’t look good in your lounge. If you can only set up your studio temporarily, or if you’re on the move and have time to deploy them, acoustic blankets can be useful for taming room acoustics when hung in front of walls or placed on the floor. Although not as effective as foam traps, these are far more practical for location work. A very cost-effective and versatile product for controlling higher frequency reflections is Molton stage fabric, which is used, as the name suggests, for theatrical drapes and in film and TV studios all over the world. Molton can be purchased for just a few pounds per square meter from Amazon.

Microphone placement: proximity and axis

The key to choosing and using microphones is understanding a couple of simple principles governing how well microphones function and which can improve the audio captured by even the most modest mic, or conversely, ruin the sound captured by the best equipment money can buy.

Proximity:

Proximity concerns the distance between a sound source, for our purposes most likely a voice, and the microphone used to capture it. As a general rule, the closer a mic is placed to the target sound source, the better the audio it captures will be. Sound waves attenuate or become quieter with distance, therefore the further a mic is away from its target sound source, the weaker the signal (the sound we want to record) will be. However, this isn’t just about overall sound level, if it were we could simply crank up the audio gain on our camera or audio recorder and voila! What is even more important to understand, is that with distance, the relative level of our target audio (signal) is lower in comparison to all other sounds in the environment and also to any hiss or hum introduced by the electronic circuitry of the microphone itself and/or the camera or audio recorder we’re using (noise). This is known as SNR or signal-to-noise ratio, and what we aim for in virtually all circumstances, when recording audio, is the best signal-to-noise ratio possible! To this end, as a general rule, we aim to get the mic as close to the target sound source as we can.

Placing our mic close to a sound source inevitably means using an off-camera mic. For all mics except Lavalier mics (see below), this necessitates two completely essential pieces of equipment, both of which can be very affordable:

First, we need a microphone lead or cable of some kind to connect the now remote mic to our camera. This will usually be a female XLR to mini (3.5mm) TRS (stereo) jack plug for DSLR cameras or female XLR to male XLR for external recorders/audio interfaces and professional video cameras. Don’t be tempted to buy a 20m long monster, as this will inevitably be more trouble to manage than it is worth. In most circumstances, a 5m lead will probably do just fine. An alternative to a wired connection is using wireless, but this can be both expensive and also troublesome in some environments.

Second, we need a mic stand in order to support our mic on-set. This may be a simple clamp on a desk stand for vlogging or it could be an extra-large boom stand used for overhead mics. Alternatively, if we work with a dedicated sound recordist you could use a boom pole. When filming interviews, I personally use a boom pole clamped to a heavy 3m C-stand so I can fly in a mic in from the side and keep everything well out of shot. In addition to this, particularly if we are using a condenser mic of any kind, including shotgun designs, we will need some kind of shock mount to isolate the mic from unwanted vibration.

Axis:

Microphone axis is a more complex concept than proximity, but nonetheless important, as changing a microphone’s axis or direction relative to a sound source can subtly change the tonal characteristics of the sound it is capturing, as well as affecting the all-important signal to noise ratio discussed above. Different mics are designed to pick up sounds in a more or less three-dimensional pattern around the mic element. Some mics are designed to be directional and to pick up sounds from directly in front of the mic element more effectively than sound coming from the side or from behind. Others are designed to be more omnidirectional and to pick up from a much broader, effectively spherical field around the mic element. Others still are designed to pick up in a more hemispherical pattern above a flat surface. However, to complicate things further, directional mics don’t reject off-axis sounds from across the frequency spectrum in equal proportion, therefore a directional mic that is off-axis (pointed in the wrong direction) won’t just pick up less of our target sound, it will also change its tone, which may be desirable or not! In recording studios, sound engineers will often use the off-axis characteristics of a mic to subtly colour the sound of an instrument, and part of their skill is understanding how different mics reject different parts of the audio spectrum when placed at different angles to a sound source.

Types of Microphone and their different characteristics

Lavalier mics

Lavalier/lav/lapel/tie clip mics (choose whichever name you like best) are primarily designed to get in good and close to the source of a talent’s voice. They tend, rather counter-intuitively, towards having an omnidirectional pickup pattern, mainly because when used in such close proximity to a talent’s body a more directional mic might struggle with things like the side-to-side movement of the head. However, because they are so close to the target sound source, they can maintain an excellent signal-to-noise ratio between this and sounds in the surrounding environment. You will often see lav mics used in newsgathering situations or used with wireless systems on TV, where they can be clipped onto someone’s clothing in order to capture a very clean recording of their voice. Lav mics tend to be very small and can be deployed discreetly. The downside of lav mics is that because they have such a small mic element or capsule, the sound they produce can lack both richness and clarity, making them a less than ideal choice in many situations. They remain a staple for video production, particularly in noisier environments like trade shows. Lav mics are available for all budgets, with models aimed at shooting with a mobile device coming in for as little as £30, while top-flight units like the Countryman B3 costing several hundred pounds, more if coupled with a suitable wireless system.

Some recommended lav mics:

• Rode Smart Lav, which connects directly to many models of mobile phone
• Rode Lav, can easily be used wired or connected to a wireless system such as the RodeLink or Video Mic Go systems
• Sennheiser EW G4 Wireless with ME2 Lav mic, probably the closest thing we have to an industry-standard wireless lav mic

Small Diaphragm Condenser mics

Often overlooked in favour of shotgun microphones, small diaphragm condenser (SDC) or pencil condenser mics are a staple of the recording industry, often used as overhead mics for acoustic instruments. They also perform exceptionally well when used indoors to record dialogue for video. Perfectly respectable SDCs can be purchased for as little as £100 and because of their price point are often purchased as matched pairs for stereo recording. One point to remember with SDCs or any other type of condenser mic (also sometimes called a capacitor mic) is that they require power to create a potential difference across the condenser/capacitor. This can be either from internal batteries or from 48v phantom power provided by a video camera or an audio recorder. Because they require phantom power and therefore have an XLR output connector, they cannot be plugged directly into a DSLR camera.  These mics are renowned for sounding transparent and natural with great high-frequency definition. SDCs normally exhibit either a cardioid (quite directional) or hyper-cardioid (very directional) polar pattern, which makes them extremely useful for voice recording at more of a distance from source. Condenser mics are very sensitive, so a shock mount is essential.

Some recommended small-diaphragm condenser mics:

• SE Electronic SE7 or SE8
• AKG C1000s, which has a compartment to be powered by a 9V battery
• Rode NT5

Dynamic mics

Sometimes the simplest ideas are the most effective and this certainly goes for dynamic mics, which are very simple in design, inherently robust, and self-powered for many applications. They are a great choice for run and gun style interviews in noisy environments as they can be placed very close to the talent’s mouth and screamed down if necessary. Low on finesse but high on practicality, with perfectly respectable results if used sensibly, dynamic mics are a common choice as starter mics and will be as at home in the hands of a death metal vocalist as they will be being passed around a group of athletes during a post-event interview. Dynamic mics such as the Sure SM57 and SM58 are found on stages and in studios the world over and are regarded as both industry standards and true classics. Dynamic mics provide their own power, but may not produce a high enough gain to suit many camera pre-amps, being better suited to use with dedicated audio recorders. While dynamic mics rarely sound anywhere near as natural and transparent as condenser mics, perfectly usable results are possible with a little eq in post-production (see below).

Some popular dynamic mics:

• Sure SM58, having a slight presence peak this mic is very good for all kinds of very close voice work, would probably survive a nuclear bomb blast
• AKG D5, a little more refined than the SM58 perhaps but nowhere near as robust
• Sennheiser E835, another dynamic mic renowned for its longevity

Shotgun Mics

Shotgun mics are regarded as extremely directional, I.e. beyond hyper-cardioid in terms of their polar pattern, as they are designed to reject sound from the sides using the physics of phase cancellation. Suffice it to say that they are extremely good for recording voices at a greater distance while preserving a good SNR with ambient sounds and are frequently seen on boom poles above the heads of talent in the TV and movie industries. They also have a tendency towards enriching low-frequency information when used very close to the target sound source (known as the proximity effect), which makes them a popular choice for voiceover work in some circles (think Don LaFontaine). When working outdoors, shotgun mics are invaluable and can be used to focus on the voice of your talent like a laser, even from several feet away, making them easy to keep out of the shot. Contrary to popular belief, however, shotgun mics aren’t always the best choice for indoor use, as early reflection information from walls, can play havoc with their phase cancellation properties, resulting in what is known as comb filtering, where narrow frequency bands are cut or boosted quite sharply resulting in an unnaturally coloured sound. 

Most shotgun mics require phantom power from the camera, with some being self-powered from an internal battery. Mics described by manufacturers as video mics are of a shotgun design, as their ability to isolate more distant sound sources makes them better suited to being mounted on camera than other mic types, though this is never ideal. Like SDCs shotgun mics are very sensitive and require a shock mount. Shotgun mics are sometimes handheld by news reporters, who mount them on special hand grips with built-in shock mounts. Because of their sensitivity, shotgun mics are invariably used with furry windshields or dead cats, when used outdoors. Even more effective blimp windshields are also available.

Some popular shotgun mics:

• Rode NTG series
• Deity S Mic 2
• Sennheiser MKE 600, which can be battery powered, making it ideal for use with a DSLR

Monitor your audio whenever you can

Obviously, if you are the talent in your video, you may not want to appear on screen sporting headphones, but in all other circumstances, monitoring the audio going into your camera or audio recorder is always the best way to spot any issues as you are recording! No one will have a problem taking a scene again if you spot a problem and make some adjustments to your audio track between takes, but you’re going to prove very unpopular if you constantly recall everyone for reshoots because you weren’t paying attention during filming. Get a good pair of isolating or closed-back headphones such as Sennheiser HD380 or Beyerdynamic DT 100, as these will help you to really zone in on the audio you are capturing. Don’t, under any circumstances, confused isolating headphones with noise-canceling headphones as these may mask problems you need to be aware of.

Record a safety track

If your camera or audio recorder allows it, simultaneously recording a safety track, maybe 10 or 12db quieter the main audio track, is always a good idea. Doing this will mean that if your talent becomes over-enthusiastic at any point and the signal from their voice begins to clip, you can substitute a portion of your safety track in post-production, thereby quickly repairing the problem. Photographers are used to doing a similar trick with bracketed exposure, which often saves the day.

Pay attention to your sound in post

No matter how hard you try, getting the audio on multiple video clips to be uniform at the capture stage, is virtually impossible. While it is always best to aim for the highest standards of audio capture during filming, a certain amount of normalisation will inevitably be required in post-production in order to unify volume levels and tonal balance between clips. However, like a lot else to do with audio, this is often overlooked with the result being a less than coherent soundtrack to an otherwise successful production. All editing software, no matter how basic has equalisation (tonal correction) and gain (volume) control available. More advanced packages may also have audio compression and limiting, both of which are designed to reduce the dynamic range of audio; however, these should be used with care to avoid an unnatural sounding result. Other audio toys include things like duckers, which automatically lower music tracks slightly when a voice enters. By all means, experiment with all of the tools at your disposal, but remember that there is rarely, if ever, a fix in the mix for badly recorded source material, so taking time to get the best result possible at the production stage is always wise.

Practice makes perfect

At the end of the day, regardless of the choice and quality of equipment available, your own ears are by far the most important link in the chain when it comes to sound recording. However, just like any other skill, active listening requires both learning and practice. In the first instance, you need to be able to discern between good and bad results, and though this is clearly very subjective in some respects, after a while you will be able to hear when, for example, an audio signal is beginning to clip, when too much room ambiance is present or when over-enthusiastic eq is causing sibilance; all of which can be judged far more objectively. Similarly, noticing incongruous sounds like hiss and hum isn’t something we do easily, as we live constantly surrounded by ambient noise that we try, either consciously or unconsciously, to block out. Just as we learn to notice when things look out of place in the frame of a video, we can, with a little work, develop similar auditory discrimination.

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