How to solve the problem of noise in the microphone?

As a security worker, in addition to various security-related skills, there is also a lot of seemingly irrelevant knowledge that needs to be understood to a certain extent, such as some common problems about microphones or microphone equipment.

What I want to share with you today is how to solve the problem when there is noise in the microphone.

1) Choose a condenser or active microphone with low self-noise

Self-noise is the noise introduced into the microphone signal by active components (such as transistors, vacuum tubes, etc.) In other words, the sound emitted by these components is picked up by the microphone.

Self-noise has a rated value, and this rated value determines the signal-to-noise ratio (the ratio of signal to interference plus noise).

Therefore, if you want to reduce the noise of the microphone, choosing a microphone with low self-noise (try not to exceed 20dBA) can be said to be an option to fundamentally solve the problem.

2) Choose a dynamic microphone with a double coil pickup

Although passive dynamic microphones have no self-noise level because they have no active components, the components of these microphones still absorb noise into the microphone signal.

This is because the magnet and conductive coil of a dynamic microphone are particularly sensitive to electromagnetic interference.

A dynamic microphone with an AC voice coil produces less noise than a dynamic microphone without an AC voice coil.

3) Use a shock mount

There is a type of noise called mechanical noise, which refers to any vibration that passes through an object and reaches the microphone capsule and causes noise in the signal.

The shock mount can effectively isolate the microphone from these mechanical noises to achieve the effect of reducing noise.

4) Use a pop filter

Hard consonants like P, B, D, T, G, and K will produce popping sounds, which are unwanted noises in the microphone signal. Therefore, the role of the pop filter is to eliminate the popping sounds when speaking and reduce noise.

5) Use a balanced microphone cable

If you are using a professional-grade microphone, it is recommended that you use a balanced microphone cable.

The working principle of a balanced cable is to transmit the audio signal to two different pins instead of one. The audio signal has positive and negative polarity on the two pins respectively.

At the microphone preamplifier, there is a differential amplifier that can add the difference between the two audio pins while canceling the common point. This is called common mode rejection.

Electromagnetic interference on the wire will generate the same noise on each audio line, and through common mode suppression, this noise can be eliminated at the microphone amplifier.

6) Do not place microphone cables and power cables together

Because the power supply (and its cables) emit electromagnetic noise, the closer the power line is to the microphone cable, the more likely the microphone cable will pick up this noise.

This is called "60 cycle hum" because the frequency of AC power is 60 Hz. Therefore, to reduce the presence of power hum, minimize the number of times that microphone cables and power cables cross each other.

7) Use RF filters

When it comes to EMI in microphone signals, there is another element called radio frequency interference (RFI), and when microphones are used in urban areas or near radio stations, there is a higher risk of RFI being introduced into the signal.

Some microphones may be particularly sensitive to RFI. To further reduce EMI and eliminate RFI from the signal, you can use RF filters and connect them to the microphone and subsequent equipment.

8) High pass filter

If the noise is a low frequency hum (from the power supply) or rumble (from footsteps, machinery, etc.), you can try using a high pass filter to reduce the noise in the signal.

Because the high-pass filter can filter out low-frequency signals in the microphone signal and allow high-frequency signals to pass through.

Be careful when high-pass filtering microphone signals, as setting the filter too high will result in a thin sound. This may not be a big deal when recording high-pitched sources, but when recording low-frequency sources (bass, tuba, kick drum, bass, etc.), high-passing the signal may not be a good choice.

9) Connect the microphone to the MIC port

This is a more reliable way to connect the microphone to an input designed for this purpose and avoid unwanted noise.

The microphone input requires a mic level signal which is usually balanced, and connecting it this way means that the signal will be delivered to a circuit that works well with it.

If you plug a microphone into a line input, you will have serious noise problems. Because the expected signal strength of a line input is 10-1000 times stronger than a mic level signal, the inherent noise in the input may be louder or even larger than a mic level signal.

10) Use a clean preamp

A clean preamp is vital to getting pristine audio quality from your microphone.

Many mic preamps provide enough clean gain to bring the signal from a powered microphone up to line level without introducing noticeable noise.

Some professional microphone preamplifiers can really add icing on the cake to the microphone signal.

But some problems arise when we use passive microphones with lower sensitivity.

Low-sensitivity dynamic microphones require a lot of gain to be brought up to line level, few mic preamps can provide that much clean gain and most will create noticeable noise in the audio signal.

Therefore, when using a low-sensitivity microphone and want a low-noise effect, it is a correct idea to choose a high-end microphone preamplifier, but the price of high-end microphone preamplifiers is often very high.

Another less expensive way to provide clean gain to a signal is to insert an additional preamplifier between the microphone and the mixer, recorder, etc.

11) Connect a series preamplifier to the front end of the microphone

Low-noise series preamps are a good choice when you don't want the price of a high-end mic preamp but do need gain.

This preamplifier can provide additional clean gain before the siganl reaches the microphone preamplifier of the mixing console, recorder, sound card, etc.

12) Use a noise reduction plugin in your DAW

If you’ve tried everything and still end up with a noisy audio signal in your DAW, you can try a noise reduction plugin.

In addition, if conditions permit, the microphone can be processed in real time through a noise reduction plug-in when recording the signal.

The advent of plug-ins has given us a way to digitally reduce the noise in our signals.