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The two golden rules of microphone placement

There is nothing in audio as important as microphone placement. So what are the ground rules for getting this right?

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Two microphones...

  • The Shure SM57 - $99
  • The Neumann U87 - $3,599.95

At such wildly different prices (offered by an online retailer in the USA) you should expect these microphones to sound different. And they do. Whether there is $3,500.95 worth of difference is open to debate, but microphone selection is an important component of recording technique.

However there is one way to make much more of a difference to the sound, using the same mic. Just move it by 30 cm (1 foot). Microphone positioning makes a hugely greater difference than microphone selection. And improving your microphone's position costs nothing but a little time.

The importance of microphone placement or positioning cannot be overstated. The professional way to do it, for any instrument or voice, is to start from a point that is known to be good from experience. Then move the mic to different positions to find the ultimate sweet spot. This is best done with two people - the engineer and his or her assistant while monitoring in a separate control room on loudspeakers. It is more difficult for one person to do this while monitoring on headphones, but the objective is the same.

But suppose you don't have so much experience yet. Or none - Suppose this is your first time setting a microphone. Where do you start?

Let's imagine you have an acoustic instrument to record, to keep things simple in mono with a single mic. You only have one mic so microphone selection isn't an issue. Let's suppose the instrument is a guitar, and suppose you want to achieve a natural sound.

Step one is to find out where in your recording space the guitar sounds best. Normally it is better to be well away from walls and hard surfaces other than the floor, but try out a few locations and see what difference there is to the ear. There might not be much difference in a small room with similar surfaces all round. But if you have the luxury of recording in, say, a local hall or community centre, there may be more options. Similarly if part of the floor is carpeted and part not - soft and hard surfaces will affect the sound differently.

So, once you have a good position for the instrument, walk around while the musician plays. Find a spot that is good to listen from. And so...

Golden Rule No. 1

Point the microphone at the instrument from the best listening position.

It would be an odd thing to do to position the microphone somewhere other than the best listening position. This might sound a little like stating the obvious, but often the obvious solution to an issue is the best solution. Or at least try out the obvious solution first before going along seemingly less promising routes.

There are exceptions to this rule. Ambience mics, the side mic in an MS pair, the fine art of angling the mic slightly to fine-tune its response to the sound source etc. But these are the very few exceptions that test the rule but don't by any means break it.

So once you have placed your microphone on a stand, in the best listening position, pointing at the instrument, you're good to go on to...

Golden Rule No. 2

Move the microphone closer to the sound source.

Remember that we're aiming for a natural sound here. But while the best listening position to the human ear would seem to offer the most natural sound, we have to consider the differences between the ear and the microphone.

The human ear is connected to the human brain. The human brain, which some consider to be the most complex thing in the entire universe, can process the sound picked up by the ears and make sense of it. It can separate out the ambience and reverberation of the room and focus in on the direct sound of the instrument.

The microphone, even if it is a directional microphone, cannot do this anywhere near as well. So what sounds good to you in the best listening position won't sound as good to the microphone - there will almost certainly be too much reverb.

To focus in on the direct sound of the instrument, all that is necessary is to move the microphone closer. How much closer should be determined by experiment. For a natural sound, aim to achieve the best balance between the direct and reflected components, as judged from the sound coming from your monitor loudspeakers.

Having followed Golden Rules 1 and 2, you're good to go. If your room has good acoustics and a low noise background, and you are working with a good musician who plays a good instrument, your recording will be first class.

More to it?

Of course there is much more to microphone placement than these two rules, especially if you're aiming for a larger-than-life sound, which is often the case other than in classical music. Stereo techniques, and methods of recording groups of instruments and voices require additional considerations. But the two Golden Rules will get you an awful long way along the route to success. I highly recommend them.

Audio

Here's a quick example of the difference between two microphone positions of just 25 cm (less than a foot). Both mics are the Bruel & Kjaer (now DPA) 4011 model. Download the zip file, expand it and import the files into your DAW for close listening. Audio Masterclass students have access to the full session with longer examples and many more microphone positions, with video. The guitarist is Audio Masterclass Featured Artist Mick Hutchings. The photo above shows one of the closer positions tested.

The above article in video form...

By David Mellor Tuesday October 10, 2017
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