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How to choose a professional microphone?

Author:admin   AddTime:2021-06-18

Many computer sound card users buy professional microphones, but because the interconnection regulations in the computer field are different from those used in the professional audio field, it is sometimes not easy to match professional microphones with computers.

In order to successfully connect the microphone to the computer, it is necessary to understand both the microphone and the sound card. Among them, the signal level, electrical impedance, connector type and wiring scheme are very important to understand each product, and can be obtained by referring to the product information or contacting the manufacturer's technical support department.

The output signal of professional microphones is very weak, less than 1mV. Although the audio input of the sound card may also be marked with "MicIn" or marked with a small microphone icon, it is usually not designed to accept such a low-level signal.

Most sound card inputs require a minimum level of 10mV; some older 8b sound cards require a voltage of 100mV. These differences mean that if a typical professional microphone is connected to the input of the sound card, the user will have to yell into the microphone and/or zoom in to a distance of about 1" in order to produce a sound card that is “audible” strong enough. Signal.

 There are two possible solutions:

 One is to increase the input sensitivity of the sound card, so that the signal from the microphone can be detected more easily. Some sound cards provide software that allows users to increase the input sensitivity or "gain", through a "click-drag" input level control, or a set of check boxes that can double the sensitivity by 2, 3, or 4.

If the input sensitivity cannot be improved, another method is to amplify the microphone signal before the sound card input. This allows the microphone signal to pass through a device called a "microphone preamplifier" or "microphone-to-line amplifier". (For example, LTO MIC TUBE two-channel tube microphone amplifier provided by Audio Online).

 If the microphone mixer can provide enough levels for the sound card input, you can also use it. (At this time, the mixer only functions as a preamplifier, not a mixing.) In either case, in order to know how much amplification is needed, and whether a particular microphone preamplifier or mixer is appropriate, all It is necessary to know the typical output level of the microphone (see the technical specifications of the microphone) and the input sensitivity of the sound card.

Impedance Impedance is an electrical parameter similar to resistance. This parameter is very important, because the relationship between the impedance of the microphone and the impedance of the connected sound card may have a significant effect on the signal actually transmitted from the microphone to the sound card. To obtain acceptable results, the output impedance of the microphone must be smaller than the input impedance of the sound card.

If the impedance of the microphone is the same as or greater than the input of the sound card, part or all of the signal strength of the microphone will be lost (called the loading effect). The higher the impedance of the microphone relative to the impedance of the sound card, the more signals will be lost.



 Connecting a high-impedance (also called "high-Z") microphone to a sound card with an input impedance of 600Ω will lose a lot of signal, so that the speaker's voice will not be heard. Generally speaking, the output impedance of professional microphones is lower than 600Ω, while the input impedance of most sound cards is 600~2000Ω, so there is generally no problem with impedance.

Connectors and wiring schemes When connecting a professional microphone to a sound card, the most intuitive problem is that the connectors used are of all kinds. Due to the limited width, computer sound cards usually can only accommodate very small connectors. The 3.5mm (1/8") "mini jack" used in most personal stereo equipment with audio players is the most common one.

The standard 1/4" and XLR connectors for professional microphones are too large to fit into a single sound card slot. Just as important as the "type" of the connector is the "wiring scheme" used. Professional microphones with XLR connectors The industry standard "balanced" wiring scheme is adopted, in which two pins carry audio signals, and the third pin is grounded. There is currently no wiring standard for the 3.5mm mini plug connector used by the sound card, so the actual wiring scheme depends on the sound card manufacturer Different for different.

The 3.5mm mini plug usually has two different structures. Most sound cards use a three-segment connector, usually called a "stereo" connector, because in addition to grounding, it can also carry two independent channels.

When it is used as a microphone connector, the end of the connector (called the end) usually carries the audio signal; the central part (called the ring) is sometimes used to carry the low-voltage DC power supply required by the microphone provided with the sound card; the third part ( (Called bushing) grounding. In a two-stage configuration or "mono" type, the end of the connector carries audio and the bushing is grounded. Usually the mono 3.5mm mini plug cannot provide DC power.

Some sound cards have an additional stereo input labeled "Linein". Its design purpose is to satisfy the stereo signal from VCR, CD player or tape player, it is not suitable for microphone input.

Dynamic microphones are compared with condenser microphones. Different types of microphones use different methods to convert the sound energy of a sound source (such as voice) into electrical energy that can be amplified, processed, recorded, or transmitted.

The two most common types of professional microphones are dynamic and condenser (sometimes called electret). The main difference with sound cards is that condenser microphones require a DC power supply to work; dynamic microphones do not require any external power supply.

The type and method of power supply required for condenser microphones are very important. They may affect whether a particular professional microphone can work with a particular sound card and how the cables connecting them are configured.

One type of power source called "bias voltage" powers a small transistor inside the microphone "head". The other type is called "phantom power", which is used to drive a small preamplifier with a small amplification factor or shaping the frequency response curve. The preamplifier may be located in the handle of the microphone; in the case of a small neck-mounted or gooseneck microphone, it is located in an outer tube or inside the package.

To connect a professional microphone to a sound card, when connecting a microphone with a 3-pin XLR output connector to the input end of a 3.5mm mini plug of a sound card, a special cable must be purchased or made. In order for the microphone to work properly, the type of cable connector connected to the sound card (two-conductor "mono" or three-conductor "stereo" mini plug) must be appropriate and the wiring must be correct. The correct wiring scheme depends on the type of microphone and the input wiring of the microphone on the sound card.

The following is the wiring of some common types of microphones and sound card connectors: The interface between professional dynamic microphones and sound cards, and the wiring harness connected to pins 1 and 3 of the XLR connector should be connected to the bushing of the mono mini plug at the same time.

The wire harness connected to pin 2 of the XLR connector should be connected to the tip of the mini plug. If the sound card uses a stereo mini plug, the above configuration is slightly different. The wiring harness connected to pins 1 and 3 of the XLR connector should be connected to the sleeve of the stereo mini plug at the same time.

The wire harness connected to pin 2 of the XLR connector should be connected to the tip of the mini plug. The ring of the mini plug is suspended because the dynamic microphone does not require an external DC power supply. Sometimes, it is impossible to say that the connector on a certain sound card is mono or stereo.

If you plug a cable with a mono connector into the input of a sound card with a stereo connector, the microphone will still work. This is because the ring of the sound card socket is in contact with the sleeve of the mini plug connected to the microphone cable, which will ground any DC reference voltage.

The interface between a professional condenser microphone and a sound card, and the interface between a professional condenser microphone and a sound card may be complicated, because the reference voltage varies greatly between different microphones. (Phantom power has been defined and conforms to audio industry standards. It is always the same regardless of the brand, but no sound card can provide this type of power.

There are several possible solutions:

(1) If the microphone relies on the internal battery to work, there is no need for an external power supply. The microphone can be connected to the sound card according to the same wiring diagram as the dynamic microphone. For example, AKGC1000S.

(2) If it is a handheld or gooseneck microphone with its own preamplifier, which requires phantom power, it cannot be directly connected to the sound card (because the battery may not be suitable). This type of microphone must be connected to a dedicated phantom power supply or a microphone mixer with this function; then use the same method as a dynamic microphone to connect the power supply or the output of the mixer to the input of the sound card. AKGC1000SC2OOOBC3000BBERHRINGERB-1 and so on.

(3) If the microphone is a neck-mounted, head-mounted or other type with a separate tube or box preamplifier, and the amplifier requires phantom power, it is possible to bypass the preamplifier and connect the microphone directly To the input of the sound card. If the sound card can provide the same bias voltage as the preamplifier, this is only an option.

Let the condenser microphone work under the voltage of the sound card. Some condenser microphones work with a bias voltage from the sound card. The bias voltage is usually 3-9V DC; some microphones work at a certain voltage range, and some require a certain voltage. In order to make the condenser microphone work directly with the bias voltage provided by the sound card, the cable connecting the microphone to the preamplifier needs to be replaced or improved.

Therefore, it is very important to understand the requirements of the microphone and wiring diagram, as well as the bias voltage value of the sound card input. In particular, it must be known whether the cable connecting the condenser microphone to the preamplifier is a one-wire shielded cable or a two-wire shielded cable. If this is not certain, do not proceed to the next step. Remember that signal level and impedance are still very important. The impedance of a condenser microphone that only works under a bias voltage may be higher than that of a microphone connected to a preamplifier. The output impedance of the microphone should be less than or equal to the input impedance of the sound card.

Two-conductor shielded cables are common. One conductor carries audio signals and the other provides DC power. The shielding layer is grounded and should be connected to the sleeve of the mini plug. The bias wire should be connected to the ring, and the audio wire should be connected to the end of the mini plug. If the condenser microphone uses a shielded cable with one wire, the wire carries both the audio signal and the bias voltage. In this case, some additional circuits must be added to separate the audio signal from the bias voltage. The circuit consists of a resistor and a capacitor, which are fixed in most detachable miniature connectors. Here again, it is recommended to contact the microphone manufacturer to ensure that it can work with special microphones.

For other microphone issues, how long should the microphone cable be? Because the input of the computer sound card uses asymmetrical wiring, if the length of the microphone cable exceeds 15 meters, electromagnetic interference will usually occur or the sound will disappear. In order to maintain the sound quality, make the microphone cable as short as possible. Is "polarity" Important? If pin 3 of the XLR connector is connected to the tip of the mini plug instead of pin 2, the polarity of the signal will be inverted. The human ear sounds the same as the microphone sound; but the voice recognition software may The waveform cannot be recognized, resulting in a higher error rate.

Use non-XLR connector microphone audio source: If the microphone or other type of audio source has something other than the three-pin XLR connector, you should do a little research to figure out which part of the connector carries the audio signal. That part is grounded. The audio signal should always pass through the tip of the sound card's mini-plug connector, and the connector sleeve should be grounded. The ring of the stereo connector is suspended. The cable for this purpose has a mono 1/4" phone plug at one end, and a 3.5mm phone plug at the sound card end, with the ring hanging in the air. The standard audio cable combined with the adapter can also meet the conditions.
The tip of a microphone with a 1/4" plug usually carries audio, and the casing is grounded. The impedance of this type of microphone is usually high (about 10kΩ), that is, only a fraction of the total input signal is transmitted To the input end of the sound card with a low impedance value (600Ω~2kΩ).

Summary: When connecting an audio device to a computer sound card, there are many variables that must be considered. Keep in mind that the structure of the input end of the sound card may be different from the one described here. If the technical information provided by the sound card is unclear, please call the manufacturer. But in either case, the information described in this article will help you find an appropriate solution.

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