4: Good Sound

Disregard good sound at your peril. It’s often said that good pictures and bad sound will lose you an audience, whereas average pictures and good sound will keep an audience.

Most camcorder users rely upon the cam’s built-in mic to capture sound.

For the occasional holiday video or record of a family gathering, this is often adequate, but when it comes to recording and mixing a more professional-sounding video production, the cam’s internal mic is often woefully inadequate.

Their dynamic range is restricted, they pop at the slightest puff of wind and they can sound horribly tinny when played back through a decent hi-fi sound system.

To be fair to manufacturers, they’re caught between a rock and hard place; they’re applying compromise design principles in order to keep everyone from the once-a-year user to the enthusiast happy.

Furthermore, they know that mics need to be at the front of the unit yet inconspicuous and must record the sound that’s meant to be recorded and not the system noise and motor whir af the cam itself. These microphones are often of the electret-condenser type, and produce a generally limited frequency response.

They’re pretty useless at capturing those nice, round low frequences associated with bass guitars, bassoons and even the lovely, tremor-like, rumble of surf on a west-coast beach – largely because their sensitivity is usually up in the higher and middle frequency ranges. Built-in mics are not known for their low frequency response characteristics.

In this situation, there’s only one course of action – buy an external mic. No matter how good a cam’s built-in microphone is, there’s no substitute for a separate microphone positioned close to the source.

For someone speaking to the camera at a distance of, say, 3 metres from the lens, you’ll be mistaken for thinking that the sound recording will be adequate, even indoors. For this reason, it’s worth investing in at least one external microphone that you can place near, or even attached to, your subject.

Bare necessities

The choice of microphones can be daunting for the beginner, but for the hobbyist whose aim is to acquire a general, directional, microphone that can alternately be attached to the camcorder during general shots and which can be either hand-held by the presenter or placed onto a mic stand at other times, then there are several high-quality micophones to choose from. It’s very much a question of what you expect to be doing, of course.

If you’re hoping to record the dialogue of, say, a group of people arranged in a semi-circle, your best bet would be to position a microphone where they could all be picked up equally. But what sort of microphone would it be?

A microphone’s sensitivity is classified according to the type of pickup contained inside it. What you want in this instance is a mic that is good at picking up sounds immediately in front of it but not so good at picking up the sound either side. Ideally, you’ll use a microphone with a cardioid sensitivity pattern. This will enable the sound from each speaker to be recorded in roughly equal proportions.

If a directional mic were to be used in this situation, you’d end up with a recording in which the sound of the person immediately in front of the mic would be predominant.

Different types of microphones are designed to do different jobs, and that’s why a good sound recordist will have a variety of mics in a sound kit. Sometimes, you might be called upon to close-mic a speaker in a hall whilst at the same time pick up some of the atmosphere of the venue. Add to that the fact that high quality stereo is required, and you’ll find you’re already have to think ahead.

For a solo speaker, it might be that a good quality capacitor mic – like the Audio Technica ATR30 – mounted on a sturdy mic stand will do the trick. But what if the speaker plans to go walkabout?

Well, providing that the movement is restricted, you could get away with a clip mic (alternatively called a tie-mic) like the surprisingly high quality, low-cost Canford Audio LEM-3 (as pictured, right).

You’ll need a long length of extension cable, of course – and don’t skimp on the quality.

If the speaker needs to go on a longer walkabout, you’ll probably need a radio mic; low cost versions tend to be very tinny, and it’s often worth hiring in a professional kit for the day if the job warrants it.

For a decent stereo effect, you’ll need to look at ways of flying a couple of microphones to the left and right of the “sound stage” respectively in order to give a good mixed stereo spread to your hi-fi recording.

Place a couple of cardioid mics either side of the hall, and well above people’s heads, and feed the sound back to a sound mixer, where these can be positioned L and R in the mix, and where it will be balanced with the individual mic sources – such as the speaker mic referred to above.

There are several good stereo mixers which can be used for this purpose – but enlist the help of someone who knows how to fly a mixer in a live setting.

Gone fishin’

Many readers will be familiar with the method of placing a directional microphone onto the end of a telescopic boom – called a “fishpole” in the business – and holding it in position over the main sound source.

Used with an appropriate rifle-mic like the Sennheiser MKE300 or even one of the modules in the Sennheiser K6 kit (containing one of each of a cardioid, hypercardioid and omnidirectional mic element), the mic can be placed in the most optimum position. Make sure that the mic is protected by a good shock-proof cradle and, if shooting outdoors, that it’s protected from wind noise by a “hairy harry” windshield.

A question of balance

Where consumer-format camcorders and sound accessories differ from their professional counterparts is in the way that the electrical signals are sent down the cable to the mixer or recorder.

Pro sound sources use three-pin XLR “balanced” audio connectors, whereas most consumer formats use either a 3.5mm or 6.3mm jack (stereo and mono) unbalanced line as pictured left. A balanced line uses both an in-phase (“hot”) and an out-of-phase (“cold”) connection, together with an earth strap. The idea is that the effects of hum and interference that can occur in longer cable runs can be minimised as the hot signal connection counteracts with that of the cold phase.

Consumer cams’ mic sockets are almost always a single-pole jack with only a signal wire and earth connection, so you’ll need to either buy a set of converters, or wire up your own conversion cables. Alternatively, you could always fork out for a conversion box of the sort used by broadcast DV cam users – like the Beech Tek box or the VideoAge DXA-4.

It’s in the cans

Perhaps it goes without saying that if you – or a colleague – have responsibility for monitoring sound, then don’t skimp on the “cans”. A good closed-cup pair of headphones is essential of you’re serious about sound, so buy the best you can afford.

Sensitivity Patterns

There are essentially three main types of microphone sensitivity pattern. They are cardioid, hypercardioid and omni-directional. Cardioid mics are so called because their pick-up pattern resembles a heart shape. Look at its polar diagram and you’ll see that it’s useful for recording sound in a sweep that extends approximately 45 degrees either side if it.

Cardioid mics aren’t that sensitive to sounds originating from behind the mic. A hypercardioid mic limits the range of sensitivity to sounds coming from a narrow field in front of the mic.

If, however, you’re looking to record several sound sources which arrive at the mic from various angles, then you’ll need an omnidirectional mic. These are much more sensitive to all-round sound sources, and are useful for group dialogue and general atmos recording.

Microphone Pick-up Types

Sound waves are converted into electrical signals in two principal ways – by using either capacitor microphones or dynamic microphones.

The principle of the capacitor – otherwise known as a condenser – microphone is that sound waves hit an electrostatically-charged plate. The movement of the plate causes the capacitance to vary, and it’s this change that is picked up and amplified.

A more recent, and lower cost, addition to the capacitor family is the electret condenser, found in many cheaper microphones – from built-in mics on camcorders to tie-clip mics and even hand-held mics – whose internal pickup plate is permanently charged with power from a resident battery supply. Their quality is not as good as their more expensive cousins, and will drop as the battery supply decreases.

Dynamic mics are also called moving coil mics because of their resemblance to a dynamo – the electrical energy results from the movement of a moving coil within a magnetic field. As sound waves hit a diaphram attached to the coil, it vibrates, and electrical signals are then passed to a built-in transformer which regulates the signal according to the sensitivity of the recording system.

By and large, capacitor (condenser) mics are preferred by professional users, especially in general recording situations.

Get Connected

Being serious about sound means acquiring more than just the mics themselves. You’ll need to invest in a lot of cable, for a start, and this should be the best mic cable you can afford – and lots of it.

Table-top mic stands, gaffer-grips, tape of varying colours for cable identification – they all become essential in time. Connectors – whether they be XLR, jack or phono – should be of high quality, and able to withstand the rigours of day-to-day use.

It’s useful to accumulate a kit of adaptor plugs and “sex-changers”, too; you can never have enough – and you simply never know when you’ll need them.

Words and pictures: Colin Barrett, SimplyDV. No unauthorised reproduction or distribution. Copyright 2002-2009.