Recording Sound - Microphone Choice [Part 2]

Click here for Part 1

Coming straight from part 1, there's a little more to learn about microphones. Obviously, we now know that dynamic microphones are great for high volume sounds, where as condensers are great for their dynamic range and sensitivity. What we're going to touch on next is the variation in sizes and shapes, as well as the 3D pattern at which sound is picked up relative to the diaphragm.

Rode NTG-1 with a smaller
1cm Diaphragm

Microphones are designed to receive sound. However, The way in which this is achieved varies widely depending on the size and polar pattern of a microphone. So what does this mean? Well imagine a set of speakers. The speaker cones come in several different sizes to help represent the broad range of frequencies. Tweeters are usually about 1" in diameter and deal with anything from 7-22kHz, with 4-5" cones handle the mids at 400-6Khz, which leaves large 10" cones that will delivery the very deep 20-300Hz range. This is no different for microphones.

AKG C414 with a larger
1" Diaphragm

The best way to think about this is setting up and recording a drum kit. The first part you may want to mic up is the snare drum. As the frequency range tends to be low to high mids (500Hz-5kHz), you won't need a large diaphragm microphone in order to fully replicate the sound realistically. Similarly, you won't want to use a pencil condenser microphone with a 1cm diaphragm; this would be more useful on the cymbals which create a lot of those higher frequencies. For the kick drum, which has a fundamental frequency ranging from 50-200Hz, the diaphragm on the microphone would need to be much larger: about 1" for most proprietary kick or condenser microphones. Some may even want to convert a medium sized speaker cone into a microphone, which would be able to pick up the sub frequencies of the kick (20-60Hz). However, I digress: can you tell which instrument I play yet?

The point is, before you pick a microphone, consider the frequency range that the source will be creating, or at least the frequency range that you'd like to use.

Now, polar patterns. Have you ever wondered why microphones are the shape and size they are? Why some are long and thin, where others can be cuboid-like or have the diaphragm exposed on 2 sides? These different designs have all been implemented for the purpose of creating a pick up pattern; better known as the Polar Pattern.

The Polar Pattern is a 3D shape (usually depicted in 2D) that highlights the area around a diaphragm that can pick up sound. There are 4 main patterns available for microphones, which are described below:

Omni-Directional Polar Pattern
credit:wikimedia.org

Omni-Directional - This is the simplest pattern available for a microphone and is the most basic to understand: it picks up sound from all directions equally. You can imagine the pick up pattern as being a large sphere around the diaphragm. This pattern can be found on a lot of vocal microphones and as a choice on many higher end condenser microphones.

Uses: As it works to pick up everything, it tends to give the most realistic representation of the sound, with both the source and reflections on the recording.

Cardioid Polar Pattern
credit:wikimedia.org

Cardioid - This pattern, much as the name may depict it to be, is shaped like a heart. Rather than picking up sound from all directions, it's only able to reach sounds on one side, with minimal 'leakage' of sound from the back. As you can see, there is a small amount from the rear, which is only due to the nature of a diaphragm being effected from either side regardless; for the most part though, this is a single direction pattern.

Uses: This pattern is particularly useful in both live and studio settings, where sound leakage may want to be avoided. For live purposes, you'll want to prevent as much leakage from other instruments as possible, so recording in this single direction very much helps. Similarly, if you want to record in a studio with as little reverberation as possible, the cardioid pattern should help with that.

Hyper-Cardioid Polar Pattern
credit:wikimedia.org

Hyper-Cardioid - Coming directly from the previous pattern, Hyper Cardioid is almost an exaggerated version of Cardioid, which is far more directional, leaving even less leaked sound or room tone to affect the source sound. However, what it gains in it's precision it looses in it's mono-directionality. I.e the pattern turns more into a figure-of-8 shape, which means sound is picked up from the rear. This shouldn't be significant enough to burden a recording though, especially with higher end microphones.

Uses: As this provides a more precise directionality, it is usually used for broadcast recording. For example, a lot of shotgun condenser microphones (such as the NTG-1 shown above) use this pattern so that the newscaster, who may be stood outside of a building or built up area, is picked up clearly at a distance without too much of the external noise being picked up.

Figure-of-8 Polar Pattern
credit:wikimedia.org

Figure-of-8 - Most common for condenser microphones which are exposed either side, figure of 8 is a fairly self explanatory recording pattern: sound is picked up equally from either opposite side of the diaphragm. By having this, two sources can be picked up either side of the microphone, without a large amount of spill that would otherwise occur on an omni-directional pattern. Similarly, a single source can be recorded, with a controlled amount of room tone to the desired effect.

Uses: One good example I read about recently was to use this pattern with a guitar amplifier either side of the microphone, with one guitar split and wired into both amps. As the distortion would be slightly different on either amp, this would create an almost doubled-up effect, which is naturally summed from either side of the mic to create a huge guitar sound. Also, for a lot of vocal work, you may want to record 2 singers either side of the mic for again the doubled up effect which is good for a pre-chorus emphasis.

Conclusion: These ideas are relatively simple to understand and are mostly common sense. However, knowing these simple steps and querying what your own microphones have can really change how you think about recording. Making sure the frequency response and directionality is accounted for can improve recordings greatly, especially with a combination of microphones and their respective polar patterns.

Next time, we'll go into the placement of microphones in relation to a source to make the most out of your recordings, as well as how multiple microphones can have adverse effects due to phase, with simple solutions to resolve this.

Thanks again for reading!

Alex.

Recording Sound - Microphone Choice [Part 1]

Recording Sound - Microphone Choice [Part 1]

So you want to record something. Where do you start? As you will already know, the process all starts with a sound occurring and one or several microphones picking up that sound. However, it isn't as simple as having any old microphone; there are many different types for lots of different applications. The choice of microphone you make can have a huge effect on how a sound records. In this post, I’ll go over the different microphones that are available and tips to choosing the right one for your sound.

Before I go into specifics, a little education. Most commonly, there are 2 types of microphone: Dynamic and Condenser. Each of these types bring their own uses, depending on what you’re recording:

Dynamic Microphone

Dynamic: Most common in music production and live performance, dynamic microphones use a magnet (c) and a coil (b) to pick up the sound. The way in which this is achieved is by having a diaphragm (a) attached to the coil, which surrounds the magnet. As sound waves hit the diaphragm, the coil moves back and forth over the magnet, creating a small voltage. This current is the sent down the cable (d) and converted to a sound signal used by the recording interface.

As this setup involves a magnet and coil, the movement is restricted and therefore only allows a certain dynamic range, which in turn distorts the frequency response. All be it, this is not so much a bad thing. In fact, these features are more often than not useful, which makes them very popular for recording drums, guitar amps and live vocals (the restriction allows less spill to occur from guitar and drums).

A good example of a Dynamic microphone is the SM57. This microphone is perfect for recording a snare drum, as the capsule can handle the high volumes, as well as the complimentary frequency response (right) which is boosted at around 6-7kHz, giving a nice zing to the sound. However, the response dives at approximately 15kHz, meaning the airy frequencies of a vocal or cymbals on a drum kit are not represented. This is where the condenser microphone is brought into use.

Condenser: What makes this microphone type stand out against the others is it's sensitivity. It's able to pick up and therefore represent higher frequencies much more accurately. The way in which it does this is by removing the magnet all together and instead having 2 plates (a+b) with a voltage between them. One of the plates is used as the diaphragm (a). When this plate moves, the voltage between each plates varies, which in turn gives a variable signal that can be used to convert to a sound signal.

As the voltage created between these plates is minute, an input voltage (c) is needed to boost the signal (regulated with a resistor (d)). Generally, you'll see this extra voltage boost on an interface or mixing desk as Phantom Power, or 48v for short. However, some microphones have the ability to use a small battery inside the microphone to provide this.

AKG C414 Frequency Response [source:recordinghacks.com]

A good example of a Condenser microphone is the AKG C414. This particular microphone is a staple in any professional studio, which provides recording for anything from vocals to drum cymbals, foley for a film sound track, brass instruments, guitar and bass amplifiers, acoustic guitars... the list goes on. As you can see from the frequency response, the higher end isn't dipped at all; in fact, it's provided with a lift to encourage those airy frequencies that a dynamic microphone would otherwise lose out on.

There are many more types of microphone that are used throughout the sound industry, including Ribbon, Electrostatic, Fibreoptic and so on. However, as I won't have access to these other types (purely down to budget), I won't be covering them in these first batch of posts. Hopefully in the future when I do get my hands on them (especially the Ribbon mics), I'll have a good go over with them and the advantages they provide.

Recording Types - Conclusion: The above explains (for the most part) how these types of microphones work and a couple of example of what they can be used for. In the next post, I'll go into more detail of how each microphone type can have a wide variety of shapes and sizes, as well as the varying polar patterns at which sound is recorded relative to the microphone.

Thanks for reading!

Alex.