Last Updated 3 days ago
Mic self-noise is the unwanted electrical noise produced within a microphone itself, even when no wanted sound is reaching it. It is commonly specified as an equivalent acoustic noise level. This lets a manufacturer express the microphone's output noise as the sound-pressure level that would produce the same output from an ideal noiseless microphone of the same sensitivity.
What the Specification Means
A self-noise figure is usually expressed in decibels with a stated weighting and measurement method. An A-weighted figure, often written dB-A or dB(A), is common. Lower figures indicate less equivalent noise when the measurements are otherwise comparable. The number is not a digital recording level and should not be read as dBFS.
For example, a microphone rated at 14 dB(A) does not place a meter permanently at minus 14 dBFS. The recorded level also depends on sensitivity, gain, conversion and calibration. Nor does the rating mean the microphone is making a 14 dB(A) sound in the room. It describes an equivalent acoustic input used to characterize electrical noise.
Compare Like Measurements
Different weighting curves and detector methods emphasize noise differently. A-weighted RMS and ITU-weighted peak measurements can produce different numbers for the same microphone. Do not compare one manufacturer's A-weighted value with another's differently weighted value as though the smaller number automatically identifies the quieter microphone.
Read the specification's conditions and check whether the figure is typical or a guaranteed maximum. On a multipattern microphone, performance may differ with the selected pattern or settings. A short specification table can be a useful starting point, but it does not replace listening under the conditions in which the microphone will actually be used.
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Self-Noise Versus the Whole Noise Floor
The recorded noise floor can include microphone noise, preamp noise, wireless-system noise and environmental sound. Self-noise is only the microphone's contribution. Ventilation, distant traffic and a refrigerator are acoustic sources entering the microphone; they are not microphone self-noise. Clothing movement and handling noise are also separate problems.
This distinction matters when troubleshooting. Replacing a microphone with a lower-self-noise model will not remove a nearby air conditioner. Likewise, changing to a quieter preamp cannot remove noise that the microphone has already added. Identify the dominant source before deciding which equipment or recording technique needs to change.
Why Quiet Sources Reveal It
Self-noise becomes more noticeable when the wanted sound reaching the microphone is weak. A loud, close source may sit comfortably above it, while a distant whisper or delicate environmental recording may not. Raising the recording gain raises the microphone's wanted output and its existing noise together.
Imagine recording a soft fabric movement for an effects library. A microphone that performs well on a loud voice might reveal objectionable hiss when the fabric recording is brought to a useful playback level. A lower-noise microphone, a better recording distance or a quieter location may each help, but they solve different parts of the problem. Test the actual source rather than judging only a familiar spoken-voice sample.
Relationship to Signal-to-Noise Ratio
Some microphone specifications express noise as a signal-to-noise ratio using a 94 dB SPL reference sound. Under matching A-weighted conventions, subtracting the equivalent self-noise figure from 94 gives that referenced SNR. A 14 dB(A) self-noise value would therefore correspond to 80 dB under that particular convention.
This is not a promise that every recording will achieve an 80 dB separation between dialogue and noise. A real source may be much quieter than the reference, and the room and other equipment add their own contributions. Keep the manufacturer's standardized comparison separate from the practical signal-to-noise ratio of a scene.
Testing for a Production
Record the intended microphone at the planned distance in a suitably quiet space, using the proposed recorder and gain settings. Include the quietest performance or effect that matters, plus a pause for assessing the background. Compare alternatives after matching the wanted sound's playback level, so a quieter playback setting does not disguise a noisier recording.
Listen for the character of the noise as well as its level, and avoid assuming every hiss is from the capsule electronics. Connection faults, interference and downstream electronics may require separate investigation. For filmmaking, the best choice balances noise with directionality, placement, size, handling and the demands of the shot. A low self-noise specification is valuable, but the cleanest usable recording comes from the whole setup working together.
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