December 04, 2023
ForewordHi everyone, I'm Mr. Lin, how to effectively prevent microphone noise? The following 15 methods are available. Let's see below! Text1. Choose a low self-noise condenser or active microphone
Condenser and other active microphones have what is known as "self-noise", which is defined as noise introduced into microphone signal by active components such as transistors, vacuum tubes, and printed circuit boards. In layman's terms, this is noise emitted by these components and picked up by microphone.
Actually, signal-to-noise ratio (SNR) ratings are given in terms of self-noise ratings of active microphones.
When choosing a condenser or active microphone, check self-noise level, anything above a rating of around 20 dBA indicates that microphone may be hissing.
If we want to reduce microphone noise, then using a microphone with low self-noise is a priority.
2. Choose a dynamic humbucking microphone
Passive dynamic microphones have no active components and therefore no noise floor. However, components of these microphones also absorb microphone noise, as magnets and conductive coils of dynamic microphones are particularly susceptible to electromagnetic interference (EMI).
A dynamic microphone with a background coil is usually less noisy than a dynamic microphone without this background filter.
3. Move microphone closer to sound source
While this does not technically reduce microphone noise, it will certainly help improve signal-to-noise ratio of microphone.
Higher signal-to-noise ratio, of course, gives a signal with less noise. This is because signal will require less gain (noise floor will not increase as much) and expected audio in signal will be much louder than noise. Placing a microphone close to a sound source increases amount of that sound source (we call it signal) compared to noise at microphone output. This can be explained by inverse square law.
The inverse square law states that as sound moves away from source, sound pressure decreases by half (-6 dB) for each doubling of distance.
This tells us that if we halve distance between microphone and sound source, "signal" (as intended sound source) will now be 6 dB louder!
So if we are interested in SNR (and not just noise), moving microphone closer to sound source will reduce noise in microphone output.
4. Use a shock absorber
Mechanical noise is main type of noise that affects microphones. It is defined as any vibration that travels through an object and reaches microphone capsule and causes noise in signal.
For example, movement of a microphone in your hand, vibration of an instrument on stage, sound of footsteps on floor in a studio, or even pleasant natural rumble of earth.
The shock mount helps to isolate microphone from these mechanical noises, thereby reducing noise at microphone.
There are two main types of microphone dampers:
The mechanical isolation provided by these shock-absorbing mounts greatly reduces intensity of vibrations transmitted through objects to microphone.
5. Use a screen protector
Many people use microphones to record vocals, and this can be seen as unwanted "noise" in microphone signal. The function of pop screen is to eliminate audible sound of spray microphone.
The hard consonants of letters P, B, D, T, G, and K produce these sounds.
By placing a pop filter between sound source and microphone, we can greatly reduce risk of microphone spatter getting into microphone signal.
6. Record in a quiet or soundproof room
This should be too obvious a hint, but it's worth mentioning.
The best example is a typical soundproof recording studio room, which is soundproofed so sound from outside doesn't get inside. They also have fill walls inside that create an acoustically dead environment where sound doesn't bounce off surfaces.
Let's look at other less obvious ways to reduce ambient noise:
7. Use a balanced microphone cable
If you are using a professional grade microphone, please use a balanced microphone cable. The most commonly used balanced cable is 3-pin XLR connector, which we refer to as Canon's male to female cable.
Balanced lines work by routing audio signal to two pins instead of one (an unbalanced line). Audio signals are positive polarity on one terminal and negative polarity on other.
The mic preamp has a differential amplifier that sums difference between two audio outputs and eliminates common ground. This is called common mode deviation.
The electromagnetic interference (EMI) that cables will encounter will create same noise on all audio cables. With common mode rejection, this noise can be eliminated on a mic preamp!
The EMI that occurs on a balanced line is almost same for both audio lines/terminals. There will actually be slight differences because wires cannot be in same exact location. But these differences are small compared to unbalanced wire.
8. Do not connect microphone cord to power cord
Because any cable is sensitive to electromagnetic interference, it is not recommended to run microphone cables together with power cables.
This is because power supplies (and their cables) emit electromagnetic interference, and closer power cable is to microphone cable, more likely it is that microphone cable will absorb this noise.
This is called "60 cycle hum" because AC frequency is 60 Hz. Therefore, to reduce presence of noise from power supply, make as few crossings as possible between microphone and power cables.
9. Use RF Filters
Radio frequency interference (RFI) is another element of electromagnetic interference in microphone signals. If you use microphone in a city or near a station, this may create a risk of radio interference to signal.
And some microphones are particularly sensitive to RF interference. Assuming that in a radio station studio, Rode NT1-A is almost immune to radio interference, while Neumann U87 Ai can make annoying white noise.
RF filters can be used to further reduce EMI and remove RFI from signal. Usually they are sent to microphone, and then filter is sent to power stage.
10. Microphone signal with high pass filter
If you hear low-frequency hum (from power supply) or hum (from street, footsteps, machinery, etc.), try using a high-pass filter to reduce noise in signal.
The high-pass filter can filter out low-frequency signals in microphone signal and pass high-frequency signals.
High frequency signals at frequencies of 100 Hz and above can reduce low frequency noise, for example:
Be careful when high-pass filtering microphone signal: setting filter too high will result in a thinner sound. While this may seem acceptable when recording high-frequency sources, a treble signal may not be best choice when recording low-frequency sources (bass, tuba, kick, bass, etc.).
Having said that, if you find that there is too much low frequency noise in your microphone signal, try using HPF for signal. Some microphones have a built in HPF (eg Neumann U87 Ai).
And in analog and digital mixer channel strips, EQ also has an HPF. There are many EQ plugins in DAWs that can effectively handle high frequencies of an audio signal.
11. Use attenuation near maximum sound pressure level
This is an interesting moment! As a general rule, louder sound source, better signal-to-noise ratio of pickup microphone.
However, with active microphones, larger sound sources may exceed maximum sound pressure level (max. SPL) of microphone.
Maximum SPL tells us point at which microphone signal will begin to distort... This is usually measured for a 1kHz tone with distortion threshold set to 0.5% THD.
While distortion is not technical noise (it is a signal change), it adds harmonics to signal, which can also be considered noise.
Values above maximum sound pressure level may result in signal saturation, but may also cause distortion. And distortion is not main reason, most unbearable is noise in environment.
Using a pad (passive attenuator) on a sound source with a good signal can effectively reduce extraneous noise in microphone signal while maintaining a good sound source.
Attenuation does not change microphone's natural signal-to-noise ratio, and reducing signal with attenuation will also reduce noise in signal by same amount as signal of interest.
Many microphones or mic pres will now have a pad function.
12. Connect a microphone to MIC port
This is a reliable way to connect a microphone to an input that is not intended for it, to avoid unwanted noise.
Microphone input requires a mic signal, usually balanced (mixers, recorders, XLR ports on sound cards). This connection means that signal will be routed to a circuit that works well with it.
For example, if you connect a microphone to line-in, this can create serious noise problems. This is because signal strength expected from a line input is 10 to 1000 times stronger than a mic-level signal, and inherent noise at input can be louder or even louder than a mic-level signal.
The mic input normally includes a mic preamp, see below.
13. Use a clean preamp
A clean preamp is critical if we want to achieve flawless sound quality from our microphones.
Many mic preamps provide a clean enough gain to amplify an active microphone signal to line level without noticeable noise. For better or worse, some professional mic preamps can actually add color to a mic signal.
The problem starts when we use passive microphones with low sensitivity.
Low sensitivity dynamic microphones require high gain (sometimes up to 80-100dB) to reach line level (active microphones may only need 30-60dB). Few mic preamps offer such clean gain, and most amps produce noticeable noise in audio signal.
So if you are using microphones with low sensitivity (on quiet sources) and want to achieve low noise levels, a High End class mic preamp is way to go. But... such a high quality amplifier costs a lot of money...
Another less expensive way to achieve clean amplification is to insert an additional (low noise) mic preamp between mic and mixer, tape recorder, sound card, etc.
14. Connect serial preamp to front end of microphone amplifier
If you really need amplification and can't afford an expensive mic preamp, you might also consider using a low noise commercial preamp.
This type of preamp provides additional clean gain before signal reaches mic preamps of mixing consoles, recorders, sound cards, etc. For example, Cloudlifter CL-1, which provides up to 25dB of pure gain and runs on phantom power.
15. Use noise reduction plugins in your DAW
If above methods don't work and you end up with noisy audio signals in your DAW, here's one of dumbest ways to choose a noise reduction plugin.
Alternatively, if your computer has a lot of processing power, you can process microphone in real time using noise reduction plug-in while signal is being recorded.
Sometimes we can't completely clean up a microphone signal, but fortunately we live in an age of plug-ins that can digitally reduce noise in signal.