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Microphones are responsible for the first conversion (from acoustic to electrical energy). There are various specialists for a wide variety of applications.
Basically there are pressure receivers and pressure gradient receivers.
A pressure receiver has a membrane that closes a sealed system. It reacts directly to changes in air pressure - similar to a barometer. Microphones of this type pick up the sound from all sides. Therefore these microphones have a omnidirectional characteristic. Pressure receivers are the most natural-sounding microphone types. On the one hand because they can transmit frequencies down to almost 0 Hz, on the other hand because their omnidirectional characteristics have a very smooth frequencyresponse from all sides. A disadvantage of these microphones is their high mechanical and acoustic sensitivity. But they can be a revelation in good-sounding rooms. Interestingly, pressure receivers also have a proximity effect. However, this is the opposite of other microphones: The pressure build-up emphasizes the highs and not the lows.
In the case of pressure gradient microphones, the membrane closes off a partially open system. Through slots in this system, changes in air pressure occur on both sides of the membrane so that they cancel each other out. The microphone only responses to differences in air pressure in front of and behind the membrane. By cleverly arranging these slots and using "delay elements", the various directional effects result:
Pressure gradient receiver can have different directional characteristics. Basically, the different directional characteristics can be designed in two ways:
1.) Mechanically By using pressure gradient capsules with cleverly placed slits behind the membrane and delay elements, any desired directional characteristic between omni and figure of 8 can be created. 2.) Electrical Here two cardoid capsules are glued close together. The different directional characteristics arise through different electrical interconnection: If both capsules are switched an omni is created. If only the front capsule is switched a cardoid polar pattern is created and if the rear capsule is switched with reverse polarity, a figure of 8 polar pattern is created.
The Polarflex system from Schoeps makes use of this. Here, 2 microphones, one with an 8 characteristic and one with an omnidirectional characteristic are phase inearly mixed in three frequency bands. As a result, any directional characteristic can be achieved for these frequency bands; even after recording.
In theory, omnis receive sound equally from all sides. Due to the shadowing of the microphone body, this is no longer completely true at frequencies above approx. 2 kHz. Omnis can be created in two ways: Mechanically by using one pressure receiver capsule or by using two glued together cardoid capsules that are electricaly interconnected
... have a strong attenuation of rear sound with approx. 25 dB. Many cardoids have an unstable polar frequency response. This means that sound coming from the side is captured colored. Microphone manufacturers hower only show the "on axis" frequency response. In principle, the following applies: the larger the membrane, the greater the coloration from the side.
... have a very strong attenuation of lateral sound and a bit slighter attenuation of sound from behind. The coloration of the off-axis sound of cardoids apply here even more, which leads many sound engineers to avoid super and hypercardioids for high-resolution recordings. Some manufacturers, especially Schoeps, have solved this balancing act very well. The capsules MK 41 and MK 41v are excellently suited for high resolution OCT and XY) recordings.
With these capsules, the microphones move acoustically closer to the music.
The open membrane is a special case of pressure gradient receivers. It can usually be found in ribbon microphones and can be used equally from both sides. However, there are also a few small diaphragm condenser microphones in this design (e.g. Schoeps MK8 and Neumann KM 120) This design leads to a figure of 8 characteristic. This comes with strong attenuation to the side and a very fine, free, neutral response. It should be taken into account that, in contrast to the omnidirectional characteristic, rearward sound components are transmitted in a phase-inverted manner. Due to the high wavelength, low-frequency tones hit both the front and back and cancel each other out, which is why these microphones have a weak bass response. This also applies to cardoids and hypercardioids.
There are mainly 3 different types of microphones in professional audio technology.
...have a membrane with a voice coil attached to the membrane. This voice coil dips into a gap of a permanent magnet in time with the incoming sound. This induces a current that is passed on to the microphone preamplifier. These microphones are usually quite robust. Due to the relatively high weight of the voice coil, they are somewhat coarser and have a lower resolution. Moving coil microphones are therefore more likely to be found in live music. But there are also studio classics, such as the Electrovoice RE20 or the Shure SM 57 or the [Sennheiser MD 441](https: //the-quiet-music.company/Mikrofone-english/index.html#MD441), which cut a fine figure on drum sets or on horns.
...use the changes in capacitance caused by changes in the distance between the membrane and the counter electrode to convert sound pressure or sound pressure difference into an electrical signal, depending on the microphone type. It corresponds to the functionality of an electrostatic loudspeaker. The advantage of this design is the very light membrane, which leads to a high resolution. Condenser microphones are therefore the preferred microphones in studios.
The membrane of the ribbon microphone is a wafer-thin aluminum strip folded in a zigzag. The strip is only a few micrometers thick. Depending on the design, one or two such strips are clamped between the two poles of a permanent magnet in such a way that they vibrate slightly due to the incoming sound. The movement in the magnetic field induces a voltage proportional to the speed of movement, which is tapped at the ends of the aluminum strips. Ribbon microphes tend to have high frequency rolloff, which can be easily compensated with an EQ (when it is a good ribbon). Due to the low moving mass, ribbons nevertheless react very finely to the smallest vibrations and are by no means as sedate as the dynamic moving coil microphones. Ribbon microphones are very sensitive and are only really suitable in the studio, with the exception of the Beyerdynamic M130 and M160.
large diaphragm or small diaphragm. In general, each microphone is assigned to one of these two categories due to its diaphragm diameter.
...have a diaphragm diameter greater than 1 inch (approximately 2.54 cm). Large diaphragm microphones have physical weaknesses in the high frequency range, as the diaphragm diameter is larger than the wavelengths of frequencies over 13 kilo Hertz. The large membrane causes partial vibrations and thus discoloration. Furthermore, stronger discoloration occurs when the sound falls from the side. Why is the large diaphragm microphone considered the queen of microphones (especially among amateurs)? Due to the large membrane area, the large diaphragm microphone is particularly sensitive, which increases the signal-to-noise ratio. In addition, the timbre of a large-diaphragm microphone is often found pleasant - especially for vocals, which are generally used on-axis. Finally it should be noted that many large diaphragm microphones have a capsule with two diaphragms. By cleverly electrically connecting these two membranes, different directional characteristics can also be achieved. The physical and thus acoustic characteristics of a "real"pressure receiver or a free membrane are not achieved this way.
In contrast to the ldc, sdc have a membrane with a diameter of less than one inch and have a very good high frequency response (depending on the angle of the sound). Their frequency response foes up to well over 20 kHz. Small diaphragm microphones represent a small obstacle in the sound field and thus have less of an effect in the sound filed, which also comes into play in stereo microphone arrangements when two microphones must be placed in the immediate vicinity for intensity stereophony. Basically, the smaller the capsule, the more neutral and precise the sound. For this reason, small diaphragm microphones are used almost exclusively for recordings where sound authenticity is important. The lower sensitivity due to the smaller area, on the other hand, reduces the signal-to-noise ratio, which is still in an unproblematic range with current models from established manufacturers.
By the way: There is a persistent rumor that large diaphragm microphones have a better bass performance. This is not true Small diaphragm pressure receivers in particular can theoretically transmit sounds down to 0 Hz.