What Does Gain Do On A Microphone

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Recently, I was setting up a public address system for a presentation and was thinking about the importance of microphone gain. I decided I’d research a bit to improve my knowledge of gain and share the details with you all!

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So what is microphone gain, and how does it affect mic signals? Microphone gain increases the amplitude of a microphone signal. Gain boosts signal strength from mic level to line level, so the microphone signal is compatible with professional audio equipment. Mic preamps control gain and are the first circuits a signal passes through after the microphone output.

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That’s a brief answer. The following paragraphs will go into more detail about microphone gain and how to use it correctly.

Be sure to check out My New Microphone’s article How Do Microphones Work? (The Ultimate Illustrated Guide)!

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What Is Microphone Gain And How Does It Affect Mic Signals?

Let’s start our discussion by going over some basics of audio signals!

Analog audio signals are electronic signals. They are measured in dBu or dBV (both measurements are decibels relative to voltage):

0 dBu = 0.775 volts
0 dBV = 1 volt

Decibels are a logarithmic ratio, with +6 dB effectively doubling the voltage (and −6 dB halving the voltage). For this article, I’ll use dBu as much as possible to avoid confusion!

To improve your understanding of this article, I’d suggest reading up on decibels in my detailed article titled What Are Decibels? The Ultimate dB Guide For Audio & Sound.

Microphones are inherently analog but can also output digital signals in some instances. Gain is generally applied to analog signals. Digital gain is essentially just a multiplication of the digitized value that results in a loss of resolution.

Mic Level And Line Level

A microphone will output what is known as “mic level” signals, which are specified, nominally, between −60 dBu and −40 dBu.

However, professional audio equipment works with audio signals at line level, which is nominally +4 dBu. Notable “Professional equipment” includes mixing consoles and digital audio workstations.

Note that mic and line levels are both just average nominal values. The actual values of these levels from a microphone vary on the sound source loudness, the microphone’s distance to that sound source, the microphone’s sensitivity, the amount of gain applied to that microphone signal, and other factors.

Line level is often thought of as being around 100 to 1,000 times stronger than mic level. We need gain to boost these mic level signals up to line level so that microphones can be compatible with other professional audio equipment. From our general nominal values noted above, a 44 dB to 64 dB gain boost would do the trick.

Mic inputs expect mic level signals. If a mic input has a built-in preamplifier, the preamp should have enough gain to bring the mic signal up to line level. Plugging a line output into a mic input will run the extreme risk of overloading that input.

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Line inputs expect line level signals. Plugging a mic output into a line input will result in very low signal levels and a very poor signal-to-noise ratio.

To learn more about mic and line level signals, check out my article Do Microphones Output Mic, Line, Or Instrument Level Signals?

The Definition Of Gain

In electronics, gain is the measurement of an amplifier’s ability to increase a signal’s amplitude from the amp input to the amp output. An amp “applies” gain to an input signal to make it stronger at the output of the amplifier.

Gain works by adding energy to the signal. This energy is converted from an external power source of some sort (whether that’s an AC wall plug, phantom power, batteries, or another source).

Generally speaking, there are two possible “microphone” gain (preamplification) stages for a mic signal to pass through in practical situations:

Gain from an active preamplifier within the microphone (active microphones only)
Gain from a separate microphone preamplifier (standalone preamps, audio interfaces, mixing consoles, etc.)

Microphone gain is considered as the gain applied to mic level microphone signals.

As mentioned, this can happen inside the microphones with active circuitry. When happening with separate preamps, the microphone gain is applied to the signal coming in the mic input.

Gain From An Active Preamplifier Within The Microphone

Condenser mics and other active microphones have an active preamplifier within the microphone body. The audio signal produced by a microphone capsule is often too low in voltage and too high in impedance to be of any use.

Active amplifiers are put in-line directly after the capsule. This is to increase the voltage to workable levels and to immediately decrease the signal impedance. Low impedance allows the signal to travel through practical lengths of cable without being degraded terribly.

The gain of an active microphone’s built-in amplifier is often a fixed value.

Gain From An Active Preamplifiers In USB/Digital Microphones

USB and other microphones that output digital audio have built-in analog-to-digital converters (ADCs).

They also will typically have a mic preamp built-in before their ADC.

In this case, the built-in preamplifier should have adjustable gain to effectively bring the mic’s audio signal up to line level before it is converted into a digital signal.

The Blue Yeti is a popular USB microphone with a built-in mic preamp and ADC. It even has a built-in DAC and headphone amp and acts as its own complete interface.

For more information on USB, analog and digital audio and microphones, check out the following My New Microphone articles:• How Do USB Microphones Work And How To Use Them• Are Microphones Analog Or Digital Devices? (Mic Output Designs)

Gain From A Separate Microphone Preamplifier

Since all professional microphones output mic level signals, they all require gain to bring them to line level. Microphone preamplifiers provide this gain!

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Microphone gain is applied to the signal at the mic input of a preamp.

This is an important distinction when dealing with multi-input channels. Do not plug the microphone into a line input. Line inputs expect much stronger signals than mic level and will not provide sufficient gain to boost the microphone signal.

Audio recording and mixing, whether analog or digital, is nearly always done at line level. This means that getting analog audio to line level with gain is essential, and proper ADCs that can convert line level analog signals into digital signals are also necessary.

Mixing consoles typically have built-in preamplifiers, though standalone preamps are often preferred. When connecting a standalone preamplifier to a mixer, ensure you’re sending the preamp signal into the line input and not the mic input!

Standalone preamps may be connected to DAWs via a digital/analog converter. DAWs may also use audio interfaces to supply their mic inputs. Audio interfaces come with built-in preamps.

A mic preamp is an amplifying circuit designed to amplify a mic level input to the point of it being line level. The microphone preamp is nearly always the first circuit a microphone output signal is subjected to.

Basically, a mic preamp prepares a microphone’s audio signal for use in all other audio devices.

To learn more about microphone preamplifiers, check out The following My New Microphone articles:• What Is A Microphone Preamplifier & Why Does A Mic Need One?• Complete Guide To Microphone Preamplifier Specifications

As an aside, microphone preamps often also provide a source of +48 volt phantom power to power the active microphones that may be plugged into them.

The Focusrite Scarlett 2i2 is a popular audio interface with two combo inputs (mic/line/instrument) capable of supplying phantom power.

The Heritage Audio 1084 is an example of a standalone solid-state preamp/EQ complete with phantom power; 80 dB of Class A preamp gain, and equalizer.

Recommendations articles:• Best Microphone Audio Interfaces• Best Microphone Preamplifiers

So How Does The Microphone Gain Affect Microphone Signals?

The name of the game for microphone gain is to amplify the mic signal to line level. The amount of gain needed will depend on a few things:

The sensitivity of the microphone (signal output per sound pressure level)
The proximity to the sound source and the loudness of the sound source the mic is capturing.

Here’s an example of the first point: active mics (condensers mics, for example) have built-in amplifiers that make them more sensitive than passive mics (moving-coil dynamics, for example). Therefore, if all else is equal, a condenser mic will require less preamp gain than a dynamic mic to achieve line level signal strength.

For more on the differences between condenser and dynamic microphones, check out my article Differences Between Dynamic & Condenser Microphones.

To learn about microphone sensitivity, check out my articles What Is Microphone Sensitivity? An In-Depth Description and What Is A Good Microphone Sensitivity Rating?

An example of the second point could be that a microphone placed close to a kick drum would need less gain than that same mic placed further away from the kick drum to achieve line level signal strength. The close kick drum mic would also require less gain than the same microphone placed in front of a person doing a voiceover.

When adjusting the gain of a mic input, it’s important not to overdrive or clip the signal (typically, this is shown by a red light on the mixer/preamp/interface/etc.).

The goal is to amplify the signal to a nominal line level, making it equal in signal strength to other microphones and instruments.

Why Don’t Microphones Output Line Level?

The question begs to be asked. Why don’t microphone manufacturers build preamps within their microphones so their mics can output line level signals?

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The simple answers are history and marketing.

It just doesn’t make a whole lot of sense to change the format now when so much gear is designed the way it is.

It also doesn’t make much sense from a marketing perspective to consolidate preamps and microphones into one unit. However, the technology available now would totally make this possible.

For more information on microphone audio signals, check out my article What Are Microphone Audio Signals, Electrically Speaking?

Gain Versus Volume

When we’re plugging a microphone into a preamp, we’ll have gain control adjustment of some sort. Typically gain control is a knob. Turning the gain control clockwise increases the gain, while turning it counter-clockwise decreases the gain applied to the input signal. The gain is given in dB values.

Once we have the gain adjusted correctly and it comes time to actually use the audio signal, we’ll typically affect, route, and control the signal using a channel strip (whether on a mixing console or a DAW). Here, we’ll be using a volume adjustment (typically a fader) to adjust the volume. The volume is also given in dB values.

The purpose of gain is to adjust each instrument and microphone so that they all have equal signal strength near the nominal line level.

The purpose of volume controls is to craft the proper balance of each instrument and microphone for the mix.

Gain adjustments first. Volume adjustments second!

Pre/Post-Fader Levels On Mixers

Speaking of gain, volume, and mixers, I figured I’d write a few paragraphs on pre and post-fade levels in mixing consoles.

When adjusting the volume faders on a mixer, it usually means you’re adjusting the volume of the main outputs. However, sometimes we need auxiliary mixes that are different than the main mix.

An auxiliary mix is a mix other than the main mix. Mixing consoles often have “auxiliary send knobs” for sending a channel strip signal to auxiliary mixes. These sends can be set to either pre-fader or post-fader.

Pre-fader means the signal is sent based on the gain adjustments only. The signal is sent before the volume fader. Moving the volume fader doesn’t change the pre-fader signal level.
Post-fader means the signal is sent based on the gain and volume adjustments. The signal is sent after the volume fader. Moving the volume fader does change the post-fader signal level.

An example I’ll use to explain pre/post-fade is when someone needs a signal in their aux mix that shouldn’t be in the main mix at all.

Let’s say this is a microphone that a producer uses to talk to a sideline reporter. We need the sideline reporter to hear the producer, but we don’t want the producer to be heard through the main outs.

To accomplish this, we would do the following:

Adjust the gain of the producer’s mic to the nominal line level.
Set the volume fader at −∞ dB.
Send the channel signal to an aux mix and then to the sideline reporter earpiece.
Set the aux send to the pre-fader level.

This will send the signal “pre-fader” based solely on the gain adjustment rather than “post-fader,” which would be based on the gain and volume adjustment (in this case, there would be no signal due to −∞ dB volume level).

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