How I Podcast – A Primer on Microphones

Oct 29, 2013 | Blog, Featured, Podcasting How-to

One of the things that I’ve found to be a lot of fun in recent years is the creation of podcasts.  Podcasts are like a radio show, but distributed over the internet.  Once your phone or computer subscribes to the show (using something like iTunes), then new episodes will be delivered to your device(s) automatically and you can listen to/watch the content at your own convenience.

The podcasting that I’ve done so far is in the audio realm.  Some people create video podcasts, though that can be much more difficult to do well.  For me, I’ve been focusing on creating the highest quality audio that I can — and I’m constantly learning about how to improve!

I’ve had a number of questions in the past few months about how I put these podcasts together.  So, here begins a series of blog posts about how I create a typical episode of The SportsFathers (TSF).  TSF is a show consisting of priests who talk about sports.  We connect via Skype and it is all recorded using Logic Pro on my Macbook Pro.

This post is dedicated to microphones.  Nowadays I use a Shure SM7B dynamic (moving-coil) microphone. It has a great sound (especially in my smallish office with hard walls) and, because I already had a preamp and audio interface for music recording, it didn’t break the bank.

And so without further ado, here is some of what I’ve learned about microphones:

Microphones

Capturing the highest quality audio from the source is essential for producing a quality result. Trying to fix audio issues in post-production can be very difficult (if not impossible)!

The crucial piece of equipment for capturing the sound is the microphone. Essentially, the microphone turns the sound into an electrical signal, which can then be recorded and digitized.

There are many types of microphones available. They can be classified according to the mechanism through which they turn the sound into an electrical signal, and also by the direction(s) from which they can pick up the sound (called the “pattern” of the mic).

1. Mechanisms

• Dynamic (moving coil)

Dynamic (also called “moving coil”) microphones are essentially like a loudspeaker run backwards. A coil of wire is placed around a magnet. In a loudspeaker, an electrical signal is fed to this coil, causing it to vibrate – and sound is produced. In a dynamic (moving coil) microphone, the opposite happens: as the sound waves hit the coil, it vibrates. The vibration of the coil around the magnet produces an electrical signal, which can then be amplified or recorded.

Dynamic microphones are often fairly inexpensive and rugged. There are videos on YouTube of people generally abusing a Shure SM58 by dropping it from the top of a building or driving over it, and it still works!  Dynamic microphones can also be very good at rejecting sound reflections from the walls of a room, and they can be very good at rejecting feedback in a live situation.

However, cheaper dynamic microphones might not capture the same range of sound frequencies that other mics can capture. Ideally, people are able to hear in the range of 20-20,000 Hz.  Cheaper dynamic microphones often pick up only about half of that range.

Having said that, medium-level dynamic microphones can pick up a wide frequency range.  I personally use a Shure SM7B, which I purchased on eBay for about $300.  Since I’m typically recording in a smaller office, I find this microphone to excel at eliminating the echo that comes from the walls in the room. A Shure SM57/SM58 can also be a great choice, and they can be had for about the $100-$120 range. (The SM57/58 microphones are almost identical, except that the 58 has a ball-shaped windscreen built in.)

Dynamic microphones are often sensitive to picking up sound in a cardioid pattern (see below).

• Condenser

Condenser microphones operate using a principle called capacitance. Essentially, a thin film of plastic (mylar) is sputtered with a metal film (often gold or nickel), and this is placed very close to another metal plate. As the sound waves interact with the film, it vibrates. The electrical signal resulting from the change in capacitance is amplified and can be recorded or put through a loudspeaker.

Condenser microphones require a power source of some sort to power the electronics inside the microphone. This is usually provided either from a battery or from the mixer, which uses something called “phantom power” (a 48 volt signal which is provided on a couple of the wires in a standard microphone cable). More high-end microphones use an external power supply, but I’m guessing you wouldn’t be using those for podcasting… :-)

Because the mylar film is very thin, condenser microphones tend to be very sensitive to sound over a wide range of frequencies. This is desirable in some circumstances. However, I’ve also found that it can make cheap condensers less suitable where the room is small or has hard surfaces: they can really pick up echo from the walls of the room.

They can also be manufactured to pick up a variety of directional patterns – cardioid, figure-8, and omnidirectional are common (see below).

Cheaper microphones can introduce a noticeable amount of noise (hiss) into the signal, so be aware of this when you’re shopping. Fortunately you don’t need to spend a whole lot to have a microphone that has very little noise.

Condensers can be less sturdy than a comparably-priced dynamic (moving coil) microphone, but this shouldn’t be a problem in most settings.

• Ribbon

Ribbon microphones are also sometimes called dynamic microphones because their principle of operation is similar to that of a moving coil mic. However, instead of a coil of wire, a thin strip (or “ribbon”) of metal is placed between the poles of a magnet. The sound waves cause the metal strip to vibrate.  This vibration of the metal interacts with the magnetic field and produces an electrical signal which can be amplified and recorded.

Because the metal strip is often very thin, ribbon microphones can be more fragile than a moving coil or condenser microphone. However, the resulting signal can sound fantastic, smoothing out the higher frequencies from sources like electric guitars or horns.

A good ribbon microphone can be pretty expensive. I’ve never tried one for podcasting, nor have I heard of anyone using them for podcasting, though older ribbon microphones were apparently very common in radio in the mid-20th century.  Their directional pattern is generally a figure-8 pattern (see below).

Other microphone mechanisms exist (e.g. piezoelectric), but they are used far less commonly for podcasting.

2. Directional Patterns

The directional pattern (sometimes called “polar pattern”) of a microphone describes the direction(s) in which the microphone is sensitive to sound.  For more in-depth information, check out this Wikipedia page (which is where the graphics below are from).

Also note that some microphones let you switch between patterns, which can be useful in some situations (usually for live sound).

• Cardioid

Cardioid microphones are sensitive to sound in front of and to the sides of the microphone capsule. When this pattern is plotted on a graph, it looks sort of like a valentine heart – hence the name, cardioid.

Cardioid pattern (Wikipedia)

Microphones with this pattern are excellent at picking up what is in front of them, while rejecting what is behind them.  For this reason they are great for smaller rooms and for live sound (e.g. they are great at rejecting feedback at the pulpit in a church).

Condenser and dynamic (moving coil) microphones are often manufactured with this pattern.

• Omnidirectional

Omnidirectional microphones pick up sound all around the microphone capsule.

Omnidirectional pattern (Wikipedia)

They are often sensitive to a very wide range of sound frequencies at relatively equal levels. This makes them valuable in situations where one wants to hear a wider distance and have a more natural sound than what is sometimes possible with a cardioid pattern microphone (e.g. for a choir or for some instruments).

This can make them more difficult to use in a podcasting setup, however, because the usual desire is to only pick up the voice of the person speaking into the microphone while rejecting everything else.

It is common for certain types of condenser microphones to be manufactured with an omnidirectional pattern.

• Figure-8

Figure-8 microphones are so named because they can hear sound from the front and the back of the microphone, but not from the side.

Figure-8 pattern (Wikipedia)

This can be valuable in live situations where a monitor speaker is beside the microphone. Some sound technicians that I’ve read also like this pattern because it can sometimes create a signal that sounds more like what the human ear hears – especially when two microphones are used in a stereo setup called M/S.

I’ve often seen condenser microphones with this pattern. Ribbon microphones also naturally have this pattern, since the thin, metal ribbon will naturally vibrate to sound coming from both the front and the back of the ribbon but not from the sides.

More patterns exist (usually some variation of the cardioid pattern). Check out the Wikipedia page for more information about these.

3. Using your microphone

Once you have your microphone and everything is all connected (I’ll get into that process in the next post), it’s important to set it up in a way that works well and reduces noise in your environment.

The first thing is to use a microphone stand of some sort. Table-top stands exist, and some microphones (typically small condensers) are built into a headset. I use a cheap, boom stand, like what you see in typical church or hall setting. Because my Shure SM7B is so heavy, I’ve tied a 2lb counterweight to the other end of the boom.

Depending on the microphone you use, you may want to use a shock mount to attach the microphone to the stand. This is usually a contraption with elastic bands or bungee cords that helps remove any unwanted vibrations when you move the microphone. Part of why I use the Shure SM7B is because it doesn’t really need a shock mount. It’s pretty good at rejecting those vibrations on its own.  Other mics, such as the Heil PR40 do benefit greatly from a good shock mount.

You may also wish to use a windscreen (pop filter) of some sort. This removes excessive “pop” sounds from when you speak a “P” or “B” sound into the microphone. The Shure SM7B and SM58 microphones come with very effective foam windscreens, but other microphones need some help in this area.  This can be especially important for some condenser microphones; excessive pop or wind noise can actually damage some microphones!

It is possible to build a cheap pop filter using a small fabric loop and by stretching a piece of nylon (e.g. from nylon stockings) across the loop.  Then, a stiff wire (e.g. a pipe cleaner) can be used to attach the fabric loop/nylon to the mic stand so that the stretched nylon sits just in front of where you will speak into the microphone.

You can also purchase relatively cheap pop filters from most music/audio supply stores.

So that’s a very brief primer on microphones. I’ve had the chance to build a few condenser microphones (called “electret” type condensers, because part of the capsule has a permanent charge), and that was a fun learning experience. The resulting mics sound pretty good, though I find the Shure SM7B to be much better for podcasting in my smaller office because of how well it rejects this room’s natural echo.

In the next post I’ll talk about how I take that SM7B and record it on my laptop, along with the audio from the Skype call.