Continuing our task of expanding on each of the elements we'll be surrounding ourselves with in our home studio, today, as we announced in the previous chapter, we focus on the description, classification and examination of an element that seems so simple yet is complex and essential: the microphone.
The microphone's job is as important as that of any other component; with mics we complete our MIDI recordings, electric recordings, etc., and define the recording quality of instruments that produce acoustic waves.
What exactly is a microphone?
A microphone is an acoustic/electrical "converter" that transforms acoustic energy into electrical energy. In other words, it's the electronic device through which we convert acoustic waves coming from non-electric sources (such as instruments with a resonating body, the voice, percussion instruments and a very long list of others) into electrical audio signals.
Types of microphones
Based on how the microphone carries out its job of converting the acoustic wave into an electrical one, we can distinguish:
Moving-coil dynamic microphones
In these, a small coil picks up the movement of the membrane or diaphragm and, as the coil itself moves, a current is generated.
| Advantages: | Reasonable cost, ruggedness, ease of use; they're tough (they handle high sound pressure levels without saturating) and have low output impedance. | |
| Drawbacks: | Their frequency response is rather irregular, "peaky," and they're especially sensitive to vibration and knocks. | |
| Applications: | Given the characteristics described, I'd say these mics are especially well suited for outdoor use (because they're "not" fragile), suitable for connecting over long cables, and frequently used to pick up very loud instruments. |
Ribbon dynamic microphones
Based on the same principle as the previous ones, with the basic difference that here the conductor is a metal ribbon instead of a coil.
| Advantages: | Rugged, and they considerably reinforce the lows and mids. | |
| Drawbacks: | Heavy, irregular, weak in the highs. | |
| Applications: | Not recommended for very loud instruments. |
Condenser microphones
Basically built around a capacitor made up of a fixed plate and a moving plate (which is also the diaphragm). This type of mic requires a continuous power supply to keep the capacitor charged. Condenser mics also tend to suffer signal loss if we use cables longer than 1 meter; that's why they usually have a preamplifier built in right behind the capacitor.
| Advantages: | Flat response, high fidelity, good handling of highs and transients, good signal-to-noise ratios, low sensitivity to vibration and small size. |
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| Drawbacks: | Very sensitive to humidity, need for power, not very rugged and high cost. | |
| Applications: | Given the above, it's a recommendable microphone, except outdoors, because of its delicacy and how easily humidity can damage it. In our case, since our recording studio is an indoor space (very indoor), I think this type of mic is a good fit because of the advantages described: a satisfactory signal relative to low noise, good fidelity and good handling of the highs. |
Electret microphones
Electrets work, basically, the same way as condenser mics. They differ, however, in that the capsule doesn't need power. Even so, a preamplifier is still required, and it still draws current, except that in this case a simple battery housed inside the mic body is enough.
| Advantages: | More affordable cost and low sensitivity to humidity. | |
| Drawbacks: | Poorer response in the highs and lower sensitivity |
Mics by polar pattern
A second classification comes from their different directional characteristics, that is, the conditions or directions from which microphones pick up sound waves. They can thus be divided into:
Pressure (omnidirectional)
Characterized by the fact that (especially in small-diaphragm mics) their response is the same regardless of the direction the wave comes from.
Pressure gradient (bidirectional)
They're called gradient mics because the incoming acoustic wave undergoes a process in which the diaphragm receives it with a pressure difference, or gradient. This type of mic exhibits the proximity effect, which makes it harder to use for close-up takes, since it boosts the lows (they usually come with a bass-cut filter switch).
Combined: pressure and gradient
These are the most widely used mics. Their characteristics are similar to the previous ones, except that their proximity effect is milder.
Beam concentrator or cardioid
The function of this mic is, by means of a paraboloid, to capture the wave regardless of the direction it comes from and receive it symmetrically, even receiving acoustic signals from different directions (on the paraboloid) and redirecting them almost identically to a single receiving focal point.
Shotgun
Characterized by high directivity. The difference in wave paths that causes the phase shift occurs in a long tube in front of the diaphragm. This tube has slots through which it receives the waves, so that the diaphragm ultimately receives short signals from the front, medium lateral signals halfway along the tube and long lateral signals at its end.
Both shotgun and beam-concentrator mics are especially useful outdoors or in places with little reverberation.
What characteristics should we evaluate in our mics?
Sensitivity
We need to consider the mic's sensitivity, that is, its ability to receive acoustic signals and transform them into electrical ones. Broadly speaking, condenser mics are more sensitive than moving-coil mics.
Frequency response curve
Generally speaking, if what we're after is faithful sound reproduction, the response curve should ideally be as flat as possible in the high and low frequencies. That said, in some types of mic, depending on their function and purpose, the curve is deliberately altered to achieve certain effects or correct problems (depending on each take or situation).
Directivity
This characteristic defines the microphone's ability to pick up signals from certain directions and reject others.
Thinking about the advantages of a directional mic, I'd highlight its ability to reject, to a good extent, signals from unwanted reverberation. Among high-end mics, keep in mind that many can change their directivity by means of capsules, rotating rings, etc.
Distortion
Not at all desirable, since the distortion a mic produces is basically the sum of all the signals that appear at the output that weren't at the input, muddying the sound and hampering definition. To avoid distortion we can use "shock" filters, anti-vibration mounts fitted with elastic bands that dampen vibrations (when placed on the instrument), and every measure within our reach to isolate the mic from unwanted input signals.
Output impedance
The impedance level the microphone presents at its output. Output impedance is also affected by factors such as the length of the cable (connecting the mic to the console), the microphone's internal impedance, etc.
Power (condenser mics)
For microphones that need power, we can distinguish between those that get it from a battery and those that get it through two additional wires in the cable. There are two types of power over the cable: phantom power and AB (T-power) powering. The difference between them is quite technical, which is why I won't analyze it, in order to keep this chapter as simple to read as possible.
Noise level
The electrical nature of the microphone causes noise or slight hum to be generated, which should, in principle, be specified by the manufacturer. For good-quality mics, levels below 20 dB would be considered very acceptable.
Conclusions
I'd like to recap what has been covered in this issue, guidelines regarding microphones, so that we can choose them wisely when setting up our home studio.
I've tried to present things in a simplified but (I hope to your liking) sufficiently detailed way so that, when deciding which mics to add to our studio, we ourselves can judge which are the most suitable and complete for our needs, instead of letting someone "stick us" with a microphone that, in the long run, probably won't best cover what we're aiming for.
Depending on your individual case (how "up to speed" you are on microphones, for example), I'd go over the characteristics and types described and then compare them with our room and preferences. That is: the type of instruments or signals we intend to record (loud signals, weak ones), the size and reverberation conditions of our room, and our budget, to decide between more than one microphone specially designed for each function or, on the contrary, a versatile mic that serves us as well as possible for almost everything. In short, be very clear about what we need, and test and study which mics we're going to buy, thus minimizing the risk of making the wrong choice.
Finally, I should tell you that I had planned to devote part of these pages to the different kinds of takes: close-ups, room ambience, multi-mic sessions and the possibilities of different techniques when recording with mics, but as you can see, the subject of microphones is too extensive, and I preferred not to condense this section any further.
In short, we still have the whole part on placement and techniques with our mics, depending on the ambience we want or the instruments we're recording, but we'll jump over to the gears of our "MIDI gadgetry" so we don't end up "fed up" with so many microphones, and we'll come back to the "second part" of today's chapter later on.
