Let’s Talk Microphones
A Neumann U87 in Rhodium finish. Yes please.
In the article on equipping your home studio, I introduced the subject of microphones as an input source for recording. A couple of reader questions came in asking for a simple explanation of the different types of microphones and if there was a type that worked better for some things than others. Good questions so let’s talk microphones.
The Basics
A microphone is an energy converter. This means that it converts one type of signal into a different type of signal. In the case of a microphone, it converts sound waves into an electronic signal for recording, mixing, amplification or a combination of the three. This is the introduction to microphones so to speak, so I am going to keep things fairly high level, partly to ensure that concepts make sense and partly to avoid the need for decompression stops because microphone science can be rather deep water, although most successful microphone users never venture that deep.
Two Basic Types
There are multiple construction styles for microphones but sticking to that high level we will concern ourselves with the primary two types of microphone. They are the dynamic microphone and the condenser microphone. This is typically the first bit of information that you will see when looking at details of a microphone.
Dynamic Microphones
If you have attended a live show, or seen a speaker at a podium, or watched videos of Roger Daltrey spinning a mike, you have seen a dynamic microphone. A dynamic microphone is pointed at the source of the sound. Sound pressure moves a diaphragm with a magnet through a coil of wire. This basic principle of electromagnetics means that an electrical signal is created as the magnet moves back and forth through the coil. Dynamic microphones generate their signal without external power and because they are so simple, are quite robust and can also handle being overdriven (a source that is too loud) without being damaged. A common example of a vocal dynamic microphone is the Shure SM58, sort of the default standard for strong singers. Another Shure offering, the SM57 is commonly used to mike an amplifier cabinet. When you start getting into sound reinforcement and recording, there is no harm in having one of each in your kit.
Condenser Microphones
Condensers are a different creature. They take audio in on the sides, hence why you tend to see them in studios pointing straight up or straight down. They are not sensitive on the end. Condensers are very sensitive and respond better to subtle changes in volume and tone. This is why they are so popular in studios because they have this level of finer sensitivity. A downside to this is that they are therefore much more sensitive to too loud environments and get damaged easily if dropped or whacked. A condenser works by having the diaphragm move very closely to a charged metal plate. To keep the plate charged, the condenser microphone needs power all the time. This can be delivered by an on board battery, but most often is provided by the preamplifier using what is known as Phantom Power. It’s a 48 volt service that keeps the plate charged. Without the Phantom Power, the microphone does not generate a signal. Condenser type microphones all need Phantom Power in some way or another.
Microphone Pickup Patterns
When shopping for a microphone you should see documentation on the microphone pickup pattern. They are typically noted as unidirectional, omnidirectional and on rarer occasions, bi-directional. Unidirectional means that the microphone is most sensitive in one direction. Omnidirectional means that the microphone is sensitive in all directions and bi-directional typically refers to a figure eight style pattern, sensitive to the front and to the back but not to the sides. Unidirectional microphones are often referred to as Cardioid microphones because the pickup pattern is vaguely heart shaped. I have heard the pickup pattern described differently but will refrain from doing so. You can probably figure it out for yourself. A figure eight pattern aka bi-directional is sensitive in front of and behind the microphone. Used often for two up interviews, it’s also superb for getting both direct amp sound and reflected room sound in a single recorded track.
This graphic depicts the basic polar patterns. While we see them as two dimensional, remember that they exist in three dimensional space
You choose the pattern that best collects the sound from what you want to record. Some microphones offer user selectable polar patterns, which will make the one microphone offer more flexibility. You pay more, but it may be worth it to you.
Microphone Positioning
You can really place the microphone anywhere you choose to. I encourage trying the microphone in different positions and at different distances. Microphone to subject distance has a significant impact on the overall sound. In this regard, recordists will often leverage what is called the proximity effect. The idea is simple. The closer to the source the microphone is, the stronger the low frequency response is. If you’ve ever met a professional radio jock, that person uses this to effect. Getting close to the microphone give more bass, further away, less bass. This is particularly useful when using a microphone on a speaker cabinet. Small cabinets with small speakers tend to have less low frequency response. Move the microphone in close for more bass tone. The typical placement of a speaker cabinet microphone is about 12 inches away from the speaker cone. Moving the microphone closer will increase the bass, but if the cabinet is boomy as we find in bass guitar cabinets with large speakers in small enclosures, backing the microphone off will reduce the bass being recorded. Depending on which recording engineer you consult, you will get different recommendations. My advice is try it where you record with your own microphones and the speaker cabinets you will use. In short order, you will find a microphone position that you prefer.
We won’t get into on axis and off axis in this entry article. Know what part of the microphone to point at the sound source and point it straight at it to start. You can faff around later. :D
Microphone Output Realities
Microphones put out a very low signal level. It requires amplification, but it needs amplification such that it increases the level of the signal but not the level of the noise. This is the job of the microphone preamplifier. Studio nerds will often spend more time thinking about the preamps than about the microphones themselves. Microphone preamps raise the signal level to a point where it becomes usable for recording, broadcast or live work. Live and broadcast preamps tend to be much simpler and less sophisticated than recording preamps. In the past, a preamp was a dedicated box that the microphone plugged into, and the signal from the preamp would go to the recording desk to place on tracks and then to tape from there. Today our computer is often the recording desk and the digital recorder. That’s quite a bit simpler and less expensive than in the past, but serious recordists still want the sound of those classic preamps. You can certainly still buy hardware based preamps, but more commonly, you will buy a software based preamp model called a plug in, because it plugs in to your Digital Audio Workstation such as Logic Pro or Protools. Software preamps come in a variety of formats from different vendors. Many computer audio interfaces will talk a lot about their microphone preamps. To a large extent you do get what you pay for, but the most important thing is whether you like the sound or not.
In my case, I have standardized on interfaces from Universal Audio and UA does a ton of plugins that work with most any DAW. Their interfaces include very nice preamps, that are designed from the ground up to work with specific UA plugins (called Unison ready). So if I want my interface to have the tonality of an old Rupert Neve preamp, I can get that in the DAW through a plugin. In my opinion, it makes sense to think about the entire microphone output chain when choosing your gear. Your microphones won’t notice or care, but you will. I talked briefly about interfaces in this post.
Microphone Frequency Response
If you are of a certain vintage and were part of the whole stereo techno-rathole culture, you are already familiar with frequency response curves. It was pretty common to look at curves mapped from 20 Hertz (Hz) to 20,000 Hz. A line would show how a device would respond across this frequency range and in order to make the charts of a usable size, the charts used a Base 10 Logarithm for the X axis. Very exciting, or not, it’s up to you. Know that your body can feel frequencies as low as 20Hz but not hear them and as we age our ability to hear high frequencies diminishes. If you had excellent hearing in your teens, you may have been able to hear tones up to 17,000 Hz but as you hit middle age, you may only hear as high as 12,000 Hz. You don’t hear it so you don’t miss it, but when recording, it is a good idea to have as wide a frequency range as possible, because different people hear differently. I have lost the ability to hear past 17 kHz but still hear to nearly 15 kHz and when frequencies I expect to hear are not there, the sound starts to be muddy to me.
Every microphone has a frequency response curve. As a generalization a fairly flat response is ideal because it gives you a consistent signal and you can modify what gets recorded through the equalization process, during recording, or even afterwards using the aforementioned plugins. Many opinions exist, my preference is to record as wide a range as possible and filter later. Some microphones have a response curve that has been built to a design to favour some frequencies. Perhaps you will prefer such microphones. If you do, that’s good for you. The graphic that follows is the frequency response curve for the superb Warm Audio 87 R2 series microphone in its cardioid setting. You can see that the frequency response is fairly flat with a bit of rolloff below 100Hz, a small up swing starting around 6 kHz and then smooth falloff after around 12 kHz. This microphone is designed along the same lines as the famous Neumann U87 microphone, a studio favourite for decades, but sadly priced outside the range of most home recordists. I have tried the Warm Audio WA-87 R2 and it’s on my must purchase list
Warm Audio WA-87 R2 Frequency Response Curve for Cardioid Pattern
The WA-87 R2 Kit including storage case, direct mount and shockmount. Note the small pattern selector switch on the front of the microphone to select between Cardioid, Omnidirectional and Figure Eight patterns.
Just to be clear, I receive no compensation for my recommendations. I offer them only because I have used the product and have bought it, or plan to do so (in the case of the WA-87 R2). It is a brilliant microphone for vocals.
In Microphone Filtering
Many microphones offer in device filtering, typically a bass rolloff selector which introduces a fast shelving of sound below 100Hz. This is also called a High Pass Filter. While useful, many modern recordists choose to do this filtering in the DAW. Your choice.
Another option, particularly useful if the sound source is really loud is called a PAD. It basically reduces the microphone sensitivity by a fixed decibel amount so the sound source doesn’t overdrive the microphone capsule resulting in distortion or damage. This is particularly valuable on condenser microphones which can be damaged by excessive sound pressure.
Cables
Just as in my discussion of guitar cables, there is a difference between a good quality microphone cable and a lousy one. Review the guitar cable article for what to look for. In microphone cables as in guitar cables you do get what you pay for to a point. Gold ends and fancy strain reliefs may be more of a pocket picking exercise than a quality initiative, just as in guitar cables. Microphone cables are (for quality microphones) ALWAYS balanced, and most commonly use the three pin XLR connector. XLRs are robust and are locking connectors. Balanced cables allow for a much longer cable run than unbalanced. I would not buy a microphone that did not use XLR balanced connectors and cables.
Summary
So that’s the first dip into the microphone pool. I’ll be back with more information and a bit more to consider in a future article. For the moment, if you are hot to get started, here’s my starter microphone list. Every microphone is priced under $400 CAD and they will do a great job for you. Prices noted were as advertised on the day of writing.
Live vocals - Shure SM58 $139 CAD
Recorded Vocals - RODE NT1 Kit $359 CAD
Guitar and Bass Cabinets - Shure SM57 $129 CAD
On Grill Cabinet Microphone - Sennheiser e906 $259 CAD
Speak to you all again soon. Until next time, peace.
