Ten Minute Master No115

Any reflections and reverberations (ambient sound) that are present in a room will be

picked up by a microphone alongside the direct (instrument) sound.

Microphone positioningHow a mic is placed can make a great difference to the sounds it captures. Grant Bridgeman takes a stand...

C hoosing where and how you place a microphone is a fundamental task encountered on an

often daily basis by musicians working in a multitude of different environments and scenarios. Indeed, so fundamental is the issue that it’s rarely given a second thought, but on closer inspection, the concepts behind good mic placement and the improved results that understanding them can yield will pay dividends in both the studio and on stage.

Typically, mics are placed in such a way as to capture an authentic representation of an instrument or vocalist as heard in a live environment. The problem with this approach is that human hearing works very differently from a recording system. Our ears pick up all of the sounds that surround

us, and our brain sorts and fi lters this information according to priority. This is known as the cocktail party effect (a term coined in 1953 by British scientist Colin Cherry), which describes our ability to selectively focus on specifi c conversations that are going on around us despite being in a noisy environment.

On the recordA recording path, of course, is incapable of such intelligent discrimination, capturing every sound that arrives at the microphone’s location (the quality of the recording being dependent on the capabilities of the microphone’s individual components, of course).

To appreciate how this will affect the sounds it picks up, try walking around an instrument as it is being played. You’ll clearly notice differences in the timbre of

the sound of the instrument as your location changes in relation to it.

As you hear itOne of the most common complaints you will hear from musicians listening to a recording of themselves being played back is ‘it doesn’t sound like that when I’m playing’. The reasons for this are very simple – if not immediately obvious. When you’re playing an instrument, your ears are in a fi xed position in relation to both the instrument and the room. But when instruments are mic’ed up for multitrack recordings, the microphones are generally

positioned fairly close to the instrument to ensure they pick up the direct (instrument) sound and reduce the refl ected (ambient) sound from the room. This approach offers more control and fl exibility during the mixing process.

To accurately capture the sound you hear when you’re playing, a good starting point is to place a microphone close to your ears, which will result in less direct sound and more ambient sound being recorded. This isn’t standard practice, of course, but it does bring us back to the original question of microphone placement. A more suitable answer, therefore, may be

Instruments don’t radiate frequencies evenly – there will always be a certain ‘sweet spot’

that has the sonic colour to suit your recording. All you need to do is find it...

Refl ections Sound source Microphone Sound source Sweet spot

40 November 2007 MusicTech MAGAZINE www.musictechmag.co.uk

Illustration showing the polar response of an AKG 414: the on-axis frequency response is

excellent, but it changes very quickly in the higher frequencies when off-axis.

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Ten Minute Master No115 Microphone positioning

that ‘good’ microphone placement will capture the sound of a performance in a way that suits the production style.

For example, recording a violin in an acoustically treated environment will yield a dry recording that can be processed afterwards to simulate different acoustic environments. If you recorded the same violin in a large church, you would capture the direct sound of the violin alongside some of the reflected sound from the environment. In isolation, the violin recorded in the church would probably sound better than

the dry studio violin, but it may not suit a particular track, so the mic’ing process itself needs to be thought through as part of the whole production.

Getting closeThe reflectivity of an environment effects even close microphone positioning, which is why a great deal of consideration is paid to recording studio design to make them as acoustically neutral as possible. The acoustic influences of a room can be reduced somewhat by altering the position of the instrument within the room and using directional microphones – try positioning the source and microphone so that the rejection axis of the microphone is directed towards the ‘room’.

However, even when using a directional microphone orientated to reject the ambient sound of the room, there will still – in all

likelihood – be reflected sound reaching the on-axis elements of the microphone.

One fact that is often ignored is that a mic’s polar pattern is three-dimensional, so although a cardioid will reject sound from the rear, it will pick up reflections arriving at the sides from the floor and ceiling. This is where the distance factor of different polar patterns becomes an important consideration.

Cardioid arrestMicrophone polar patterns and frequency responses are designed to help the recording process by

offering different solutions to different recording tasks, with the cardioid microphone being undoubtedly the most commonly used design within the studio environment (and rightly so). It offers a great combination of rejection characteristics and even frequency response across the on-axis region, although checking the polar pattern is always worthwhile as there can often be less rejection of higher frequencies at the rear of the microphone.

Figure-8 microphones offer some of the most flexible positioning options, but they’re often overlooked in project studios. This is largely due to the fact that the rear of the microphone offers no rejection, making them prone to picking up room reflections. That said, the ability of the sides of the microphone to reject sound at 90 degrees to the main axis does offer many opportunities. Figure-8 mics

are often used in pairs to record two instruments in close proximity, exploiting the natural rejection characteristics to provide isolation between the instruments.

The best way to assess your microphone positioning is to wear closed-back headphones in the recording room and listen to the changes in sound that can be achieved by even small microphone movements. There isn’t a single microphone position that will guarantee a good recording (although there are excellent guides for starting points), but by listening to the

results you can achieve even with budget microphones, it quickly becomes apparent that the placement of the mic is, to some extent, more important than the quality of the mic itself.

Splendid isolation Arranging and positioning microphones would be impossible without stands and shockmounts. Stands in particular have a hard time in the studio, with constant use and over-tightening taking their toll over time.

Maintaining stands may be the least appealing of any studio tasks, but it pays to ensure that any clamps are loosened before you try adjusting a stand. This helps the clamps last longer and prevents drooping.

Shockmounts are sold with many condenser microphones and are designed to minimise structure-borne noise being

transmitted to the mic. Isolating the mic stand with a piece of carpet or specially designed isolation pads from suppliers such as Auralex can also help alleviate structure-borne noise.

There is a lot of science behind the correct placement of microphones, but simply taking the time to learn a little basic knowledge and applying it with practical experimentation can achieve excellent results. MTM

Tech Terms■ Distance factor

A comparison of the sensitivity of a directional microphone to that of an omni-directional microphone in any given direction.

■ Shockmount Suspension units that use materials with elastic properties to isolate the body of a microphone from structure-borne noise.

■ Structure-borne noise Vibrations that are carried through the solid components of a room (floor, ceiling) as opposed to through the air.

FURTHER INFO■ A concise explanation of the

cocktail party effect can be found at: http://hincapie.psych.purdue.edu/Research/Cocktail.html

■ Find technical information on numerous microphones at: www.microphone-data.com

■ The Shure website has a great range of articles in its Educational Library section: www.shure.com/ProAudio/TechLibrary/EducationalArticles

■ The Institute of Broadcast Sound has a wide range of papers and discussions on its website discussing microphones and microphone placement: www.ibs.org.uk/public/lineuparchive/index.php?dir=./2004/Feb-Mar

Many microphones – particularly high-end models – come with a purpose-designed

shockmount to reduce structure-borne noise being picked up by the mic.

Understanding how to set up mics will pay dividends in both the studio and on stage.

Isolating a microphone stand from the floor itself is another way to reduce structure-

borne noise. This can be achieved with specialist solutions or a little improvisation.

MusicTech MAGAZINE November 2007 41 www.musictechmag.co.uk