Microphone Pickup Patterns – What does that shape mean?
One of the often overlooked (or misunderstood) aspects of microphone technology is the “pickup pattern.” All microphones have some type of directionality – that is, they respond differently if a sound source is coming directly into the microphone versus from a various other angles.
If the sound source (let’s use your voice – I mean, this is a voiceover-oriented resource after all…) is coming straight into the microphone diaphragm (the moving part that changes sound waves into electrical energy), most microphones will replicate that sound to the best of its ability. As you move further to the side or “behind” the mic, that’s when things will tend to change a bit. How the microphone responds to that – in terms of capturing the energy of your voice – as you move “off-axis” is what the pickup pattern graphic represents.
You should understand that the pick up pattern graphic shows you a view from above the microphone. That graphic is from the perspective looking down on the top of the mic – as if gravity stopped working and you were pressed up against your ceiling looking down at your well-secured-to-the-floor microphone.
The Zero-degree point on that circle is the “front” of the microphone – where you might position yourself normally.
If you look at the Cardioid Pickup Pattern example here, (on some mic reference sheets the Zero-degree position is turned to the bottom), you’ll see a shape that extends out from the center. The edge of the circle is the theoretical “best” response, which means that audio coming in from that angle is not reduced by the microphone.
The pickup diagram for the Cardioid (heart-shaped) microphone pattern tells you is that the microphone is most sensitive to sound coming in from the front (where the blue arrow is), and will tend to “refuse” sound coming in from the other side (the red arrow points to that part).
The nature of that Cardioid pickup-pattern microphone is to be more directional.
It’s why periodically we tear apart all the cables and wires and gear in a recording situation trying to figure out why we have a low input level, only to find that we had the microphone pointed the wrong way. (Yes, personal experience…and easy to do with some large diaphragm condenser microphones that have cryptic external graphics.)
Anything in between the center (zero response) and the edge (maximum response) means the response is somewhere between 100% or 0% points.
In contrast, the Omnidirectional microphone in the above example will tend to pick up sound equally well from any direction – that’s why the pickup pattern graphic is a circle for that type of microphone. It’s why a certain mic might sound “noisy” in a live recording space – it doesn’t discriminate by the direction the sound is coming from.
Of course, it’s not quite as simple as that – the pickup pattern will vary by frequency, so often you’ll get a more detailed diagram from the mic maker that shows this as several overlaid shapes. In general, as you move off-axis, the high frequencies will be affected first, while you may find low frequencies continue to come through even though well away from the Zero-angle.
A simple single-shape reference supplied with many mics is probably an average, or just shows the mid-range response. The above image with overlaid response shapes is most accurate (depending of course on the quality of testing the mic manufacturer employed). If you look at the blue 16,000 Hz line, for example, you’ll see that this mic will capture less of that frequency at 60 degrees than it will capture 500 Hz sound. The red shape on the left half will indicate that low frequency sounds (125 Hz) continue to come through to the mic even at 150 degrees.
For voice actors recording in an imperfect (i.e. “noisy) environment, this directionality is generally a good thing. It can be used to reduce environmental sounds and also reduce certain frequencies – as I mentioned elsewhere, a quick way to reduce sibilance is to reposition the microphone.
Putting this information together with your microphone’s Frequency Response Curve will help you see what your microphone may be hearing within your recording space.