one of the most important things to look for in a microphone 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 the microphones 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 a meaningful input and noise
is the unwanted input to the microphone the unit of power is in watts or milliwatts the
ratio of two identical units that is what will cancel each other and make snr a pure number
however if you will look at microphone specification snr is expressed in decibel
a logarithmic decimal scale makes it more easy to understand because audio signals have a very void
dynamic range therefore snr in decibel is equals to 10 times log to the base 10 of power of signal
in watts divided by power of noise in watts using the quotient rule for logarithmic
snr in decibel is equals to 10 times log to the base 10 of power of signal in volts minus
10 times low to the base 10 of power of noise in watts in other words snr in decibel is equals
to power of signal in decibel minus power of noise in decibel the microphone manufacturers
use one pascal sound pressure with the standard one kilo hertz sine wave for testing microphones
the one pascal is same as 94 decibel SPL and it is used for the meaningful signal therefore snr
is equals to 94 decibels SPL minus power of noise in decibel 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 decibel or if you would look at Comica
Trackshot microphone it is expressed in snr and if you want to get to the equivalent noise level
just subtract 60 from 94 and you will get 34 decibel a noise level microphones with an
snr value of 74 decibel and higher are considered good and hence more expensive
you could get away with the 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 value of 94 decibel but if
you want to record a very soft sound source then snr of 84 decibel and above gives an unnoticeable
level of self-noise very low noise microphones are also called filled microphones with a snr
value of 78 decibel and above one of the quietest microphone that I have come across is Sennheiser
MKH 70 shotgun microphone with a whopping snr of 89 decibel and a price tag of 1750 us
dollars snr is relevant only to active microphones because of the inherent presence of self-noise
in active microphones 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 signals 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 microphone indirectly I
hope this video helped you to better understand signal-to-noise ratio in a microphone if you have
any questions please let me know in the comments to learn more about microphones please watch my
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