Why Microphone Self-Noise is Important to Recording

Self-noise in a microphone is important if the recordist is seeking to come as close as possible to making a clean, noise-free recording. But how does one read self-noise specs and what numbers are good and bad when making a decision on which microphone to use?

It’s a slippery question, since many microphone manufacturers — especially for low cost condensers — don’t even reveal self-noise specs. That is usually for a good reason. “It is not cheap to make a truly quiet microphone,” a manufacturer once said.

Also, some classic, high-end models from reputable manufacturers may have unique sounds and were great in their day, but by modern standards generate excessive self-noise. It is always important to read the self-noise specs before purchasing any microphone, regardless of cost.

Shure's KSM 141 noise level A-weighted is 14 dB.

Shure's KSM 141 noise level A-weighted is 14 dB.

Of course, no one wants a noisy recording, so some kind of evaluation must be made of mics before using them for recording. While a relatively noisy mic must be placed very close to the source to achieve an acceptable signal-to-noise ratio, a low noise mic offers the recordist much greater freedom of placement.

Low microphone noise is more than just a technicality. It is — in the words of premium microphone manufacturer, Neumann — your creative “elbow room.”

In a white paper on the subject, Neumann said for condenser microphones, noise is usually specified in terms of “equivalent noise level.” A more common term is “self-noise,” as this is the signal the microphone produces of itself, even when no sound source is present.

A sound proof chamber used to measure the self-noise of microphones.

A sound proof chamber used to measure the self-noise of microphones.

The proper way to measure self-noise is to put the entire microphone into a soundproof container. However, some manufacturers simply measure the microphone without the capsule. The latter method, we are told, offers better specs.

Usually, self-noise is given in dB-A. The “A” stands for A-weighting, which is a method to simulate human perception. For instance, humans are much less sensitive to noise in the low frequencies than to noise in the mid-band, where the human voice resides.

Reputable manufacturers give additional noise figures according to other (stricter) measurement standards, but most manufacturers will give A-weighted self-noise, which happens to be the measurement method that results in the lowest figures. If self-noise is not specified on a microphone, ask why.

Blue Microphone's Hummingbird has a noise level A-weighted of 8.5 dB-A.

Blue Microphone's Hummingbird has a noise level A-weighted of 8.5 dB-A.

Anything below 10 dB-A is extremely low noise, Neumann said. The exact figure is unimportant, as even a very quiet recording room will contribute quite a bit more ambient noise than 10 dB-A.

In the very good range, 11-15 dB-A, recordists may be able to discern some very slight noise in critical applications. But usually, such noise is impossible to hear in the context of the whole mix.

A range from 16-19 dB-A is good enough for most purposes. Some noise may be heard when recording relatively quiet instruments, but it’s usually unobtrusive.

When a mic’s self-noise reaches 20-23 dB-A, it’s pretty high — especially for a first rate studio-quality microphone. This is an area where every decibel counts, because we’ve reached a noise level that’s clearly audible. Such noise figures may be acceptable when recording loud sources, but not for anything below speaking level.

When self-noise climbs to 24 dB-A and above, the microphone is not worthy of being used for high quality recordings, said Neumann. This is the region where many bargain basement microphones reside.

It should be noted that self-noise is normally for condenser models and active ribbon microphones. It is rarely specified for dynamic microphones or passive ribbons. That’s because dynamics and passive ribbons have no internal electronics and their noise performance is largely dependent on the preamp being used. Those ribbons with active electronics requiring phantom power have self-noise.

As a rule of thumb, Neumann said, dynamic microphones using an ultra-low noise preamp reach self-noise figures of about 18 dB-A.

Another way to document the noise performance, Neumann added, is to specify the signal-to-noise ratio. But relative to what signal? The reference sound pressure level for noise measurements is 94 dB (which equals a sound pressure of 1 pascal).

So you can simply calculate:

Signal-to-noise (db-A) = 94 dB – self-noise (dB-A)

The actual signal-to-noise ratio in use, of course, depends on the sound pressure level of your sound source.

You might also like...

An Introduction To Network Observability

The more complex and intricate IP networks and cloud infrastructures become, the greater the potential for unwelcome dynamics in the system, and the greater the need for rich, reliable, real-time data about performance and error rates.

Essential Guide: Location Sound Recording

This Essential Guide examines the delicate and diverse art of capturing audio on location, across a range of different types of film and television production. A group of seasoned professionals discuss their art and the how it can dramatically elevate…

What Are The Long-Term Implications Of AI For Broadcast?

We’ve all witnessed its phenomenal growth recently. The question is: how do we manage the process of adopting and adjusting to AI in the broadcasting industry? This article is more about our approach than specific examples of AI integration;…

Next-Gen 5G Contribution: Part 2 - MEC & The Disruptive Potential Of 5G

The migration of the core network functionality of 5G to virtualized or cloud-native infrastructure opens up new capabilities like MEC which have the potential to disrupt current approaches to remote production contribution networks.

Designing IP Broadcast Systems: Addressing & Packet Delivery

How layer-3 and layer-2 addresses work together to deliver data link layer packets and frames across networks to improve efficiency and reduce congestion.