The noise in a microphone capsule's output refers to any signal other than the intended input source-typically unwanted elements that degrade the overall audio signal quality.
The higher the noise level, the poorer the audio quality. This noise can originate from external sources or be generated internally by the microphone itself.
Users may notice self-noise as a hissing sound that affects perceived sound clarity. For audio processing algorithms, noise reduces signal fidelity, which in turn affects overall system performance.
Different Ways to Express Microphone Noise
- Self-Noise (dBV): The RMS noise voltage output of the microphone capsule when no external sound is present.
- Signal-to-Noise Ratio (SNR, dB): The difference between the signal and the noise of a microphone capsule. It typically refers to the difference between the output generated by a 94 dB SPL (1 Pa) sound pressure input and the capsule's self-noise.
- Equivalent Input Noise (EIN, dBSPL): Indicates the sound pressure level that would produce the same output as the microphone's self-noise-effectively translating electrical noise back into a sound pressure equivalent.
For example, if a microphone has an SNR of 60 dB, the equivalent input noise level would be:
94 dBSPL - 60 dB = 34 dBSPL
This means the microphone's self-noise is equivalent to an acoustic noise of 34 dBSPL.
