What is Signal To Noise ratio (SNR) in a microphone?

One of the most important things to look for in a microphone's specification is its Signal to noise ratio or SNR. It is because SNR determines how clean the microphone's output signal will be. To select a microphone with the cleanest sound quality and minimum noise, you should aim for a microphone with the highest possible SNR value.

So, what is Signal to Noise ratio? It is the ratio of power of signal to the power of noise. Signal is the meaningful input and noise is the unwanted input to the microphone. The unit of power is in Watts (W) or milliwatts (mW). The ratio of 2 identical units, that is Watts, will cancel the units and make SNR a pure number. However, if you would look at the microphone's spec, SNR is expressed in Decibel. A logarithmic decibel scale makes it more easy to understand because audio signals have a very wide dynamic range.

Therefore, SNR in dB = 10 x log to the base 10 of Power of signal in Watts divided by Power of noise in Watts. Using the quotient rule for logarithms, SNR in dB = 10 x log to the base 10 of Power of signal in Watts minus 10 x log to the base 10 of Power of noise in Watts. In other words, SNR in dB = Power of signal in dB minus Power of noise in dB. The microphone manufactures use 1 pascal sound pressure with a standard 1 kHz sine wave for testing microphones. The 1 pascal is same as 94 dB SPL and it is used as the meaningful signal. Therefore, SNR = 94 dB SPL minus Power of noise in dB A.

Now, let's look at some examples, looking at the spec of Sennheiser MKE 600 Microphone, the noise is expressed in Equivalent noise level rather than SNR. That is just the Power of noise in dB. Or if you would look at Comica Traxshot Microphone it is expressed in SNR. And if you want to get the equivalent noise level, just subtract 60 from 94 and you'll get 34 dB A noise level.

Microphones with a SNR value of 74 dB and higher are considered good and hence more expensive. You could get away with a lower SNR if you're recording a loud sound source such as kick drum, trumpet, etc. This is because the difference between the noise and the useful signal increases, which in turn diminishes the effect of noise to the overall audio output . On the other hand, it is impractical to have a microphone with a SNR of 94 dB. But, if you want to record a very soft sound source, then SNR of 84 dB and above, gives an unnoticeable level of self-noise. Very low noise microphones are also called field microphones with a SNR of 78 dB and above. One of the quietest microphone that I've come across is Sennheiser MKH-70 shotgun microphone with whooping SNR of 89 dB and a price tag of 1750 dollars!


SNR is relevant only to active microphones because of the inherent presents of self-noise in active microphone. It doesn't mean that if you would record with a passive microphone in a noisy environment, the mic won't pick up any noise. SNR is explicitly referred to the self-noise of the microphone and not the external noises. The self-noise is generated by electronic components of the microphone itself directly or indirectly. Directly means when the desired signal passes through different components of the mic, it gets distorted and hence generate a direct noise. Or the electronic components of the mic itself produce a noise that is captured by the microphone's capsule and hence adding to the total noise of the mic, indirectly.

By increasing the sound source volume by bringing the sound source closer to the microphone and/or making it louder, we could reduce the microphone gain. The mic gain increases both the useful signal and the noise. So, the less gain we use, the less noise we get. Whatever microphone you got, you'll have to try to reduce the external noise. There are different ways to minimise external noises which I won't discuss here as they are beyond the scope of this video. But very important to consider and should not be confused with the self-noise that is expressed in the Microphone's SNR value.

If you have any questions, please let me know in the comments below 😊

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