What is a microphone and how do I use it the right way?
A microphone is used to record sound events. It converts “real” sound events into electrical impulses. Here the main focus is on the membrane, which you can find in every microphone. The membrane receives vibrations and is so set in motion. The resulting change in capacity corresponds to the microphone signal (condenser microphone). There are many different membrane types and microphone types to which we will come later.
The output rating of every microphone is relatively low. That’s because a microphone optimally is connected to a preamplifier in order to amplify the signal. You can find preamplifiers in mixers, audio interfaces and also as separate devices. Before choosing a microphone (and a preamplifier) there are many things to keep in mind.
- What do you want to record?
- What’s the loudness of your source?
- Is your room acoustically well treated?
In order to find a microphone with ideal sonic properties you first have to answer these questions. As already mentioned you also have to think about the preamplifier. If you want to use a condenser microphone you need a preamp with phantom power, because condenser microphone have a much higher output rating than (for example) dynamic microphones, which don’t need any separate power.
Microphone polar pattern
Every microphone has a certain polar pattern, a range where the microphone is more sensitive to any signal. There are microphones with a fixed pattern and there are also microphones with multiple patterns.
You can find this pattern on almost every condenser microphones with one and fixed pattern. Cardioid microphones are sensitive on the front of the microphone. It’s the best solution for bad sounding rooms, since it suppresses diffuse sound on the back side of the microphone.
On this pattern the sound is recorded equally from all sides, therefore the membrane is sensitive on both the front and the back. With a specific circuit even laterally entering sound is recorded, which makes the capsule sensitive all around. This pattern is widely used for background vocal recordings or choirs by positioning all vocalists around the microphone.
With this pattern the microphone is sensitive on the back and the front, whereby the proximity effect (the nearer the source the louder the low-frequencies) is very strong. Low frequencies spread out spherically wherefore they reach both sides of the membrane and add up. This effect is welcome if (for example) vocals do sound thin or your source needs more fundament. If your room isn’t acoustically well treated this pattern will cause problems, because diffuse sound becomes audible due to the double-sided sensitivity. The figure-eight pattern is also often used for stereo-recordings (Mid-Side technique)
There are many different topologies and designs, and all of them boast specific properties, which are suitable for certain recording situations (or not). Here the most common designs:
A dynamic microphone works with a moving coil, which superficially viewed is a reversed speaker. In contrast to condenser microphones, dynamic microphones don’t need any supply voltage (phantom power) and on certain designs phantom power even causes damage.
Due to the construction, dynamic microphones have a lower output voltage and therefore need significantly more amplification. Moving coil microphones are much sturdier than condenser microphones, which is why they’re the preferred choice on stage. Sonically they’re inferior to the more accurate sounding condenser microphones.
Ribbon microphones do also convert with the help of electromagnetic induction, which is why they’re a subtype of dynamic microphones. The transducer consists of a thin aluminium foil and two magnets. The membrane moves inside a magnetic gap. Due to the lightness of the foil, ribbon microphones are significantly more accurate then moving coil capsules. However, the output voltage is considerably lower than with moving coil microphones.
Like moving coil microphones ribbon microphones can (and have to) be operated without phantom power. In the meantime, some reputated companies came up with active ribbon microphones, which provide more output voltage, and work with phantom power. A characteristic of ribbon microphones is the polar pattern, which is always “Figure-Eight”. Due to the double sided aluminium foil it’s sensitive on both sides.
Because of the sonic properties, the great impulse response and the high output voltage, condenser microphones are dominating in the recording studios. A membrane, fitted with a very thin foil, receives the signal, which causes a change in capacity. That change corresponds to the microphone signal.
Condenser microphones have to be operated with phantom power and offer a very high output voltage. There are many membrane sizes that affect the sound of a capsule.
Large-diaphragm microphones do have a more pronounced proximity effect and have a very big larger-than-life sound. Small-diaphragm microphones come with a smaller capsule that just swings faster (due to physical laws).
The proximity effect isn’t that present on small diaphragms. That’s why SDC microphones tend to sound more precise and linear than LDC microphones.
There are many types of circuits for condenser microphones (FET, Transformer and Tube). Each of these topologies has its own characteristics. In general, the sound of FET microphones is cleaner and more natural with a very good noise level. By adding harmonic distortion to the signal the sound of tubes can be a bit warmer. The problem with tubes is the durability and the warm-up time. Cheap tubes even tend to distort.
Another problem is the noise-floor of tubes which is noticeably louder than with transistors. Microphones with transformers add some coloration to the sound and normally come with a solid noise-level.
Equalize only with the microphone
The sound of a microphone is defined (inter alia) by its direction. By changing the position of the microphone you can affect the overall sound positively. So you can just sculpt the sound even while recording.
Vocal recordings can be improved with the proximity effect. Broadcast and speech recordings can benefit from the effect which makes them sound bigger and closer. By reducing the distance to the microphone (>15cm) you can just influence the proximity effect.
Concerning the high-frequency response, the angle plays a decisive role. To attenuate the high-frequencies you have to turn the microphone by ca. 30-45 degrees. The bigger the angle the clearer the effect.
You should really take the time and adjust it carefully, which can significantly influence the overall sound quality (and the expense in post-production).
Which Microphone should I use for…?
Here the preferred microphone type is the large-diaphragm condenser microphone (cardioid pattern) which sounds larger-than-life and bigger. But at this point, it’s also a matter of taste. If it sounds good, it is good. So you can also use dynamic (or ribbon) microphones if it fits the voice.
To achieve good drum recordings you have to use a combination of LDC, SDC, and dynamic microphones.
- Bass Drum: Dynamic microphone
- Overhead: Large-diaphragm microphone
- Snare and Toms: Dynamic microphone
- Hihat: Small-diaphragm microphone
Condenser microphones are suitable for piano recordings. Depending on the desired result you can use SDC or LDC microphones. To achieve more three-dimensionality you should record the piano in stereo (AB or Mid-Side). If you want the piano to stay straight and thick in the mix you can go with large-diaphragm microphones. For more natural piano recordings juse use small-diaphragm microphones.
Same goes here: to add some more space you can record guitars in stereo. According to your personal taste you can stick with a large or a small diaphragm. If you want the guitar to be dominant and straight-forward you can use a LDC microphone. With SDC microphones the guitar sounds more natural.
Guitar (Bass) amp
The recording of a guitar or bass amp is more adventurous due to the higher sound pressure level. Because of the operating principle dynamic microphones are more robust and the first choice for guitar and bass amps.
There are also condenser microphones which can handle high sound pressure levels. It’s all a matter of taste.