Microphone Characteristics: Signal To Noise Ratio and Self Noise

And here we go! Signal to Noise!

Quick interesting fact before we dive into this discussion. I didn’t know this was an actual term when I first heard of it. It was just music to my ears… Literally! Signal to Noise is one of my favourite Peter Gabriel’s songs and I got introduced to it far before I even considered myself becoming a sound professional! Interesting coincidences! – If you check it out, I highly recommend you watch the live video from the “Growing Up” tour! The whole show is remarkable!

Signal to Noise Ratio

Now the term itself is quite self explanatory. It describes what is the ratio analogy between the actual signal and the noise that might be present in the signal we are recording itself.

Ideally, we would want this ratio to not exist at all, but in reality, there always going to be some. Therefore we strive for this ratio to be the highest possible and in that way we ensure that the noise stay so low that is barely, or not at all, noticeable. We measure this ratio with dB SPL and the larger numbers indicate mean the noise is less as it means that the difference between the noise and the signal is bigger.

This measurement is standardised as a 94 dB SPL 1 KHz tone on-axis at the microphone’s capsule. The acoustic level reference in that case is 1 Pascal (94 dB SPL).

Self Noise comes into play

Here’s where Self Noise comes into play. Self Noise is an unavoidable part of microphones. Self Noise describes the noise the microphones and their circuits themselves produce, and therefore is unavoidable.

This is measured in dBA (A-Weighted). As the reference is again at 1KHz, we can easily make the calculation here. As an example I will use my Aston Spirit again like we did in the Frequency Response article. The Spirit has a Self Noise of 14dB A-Weighted. Subtract this out of the reference point, (which is 94dB SPL) and you have 80dB A Weighted as you Signal to Noise Ratio, which is pretty decent and super usable in professional audio circumstances.

Self Noise will be present on condenser microphones as they need power to operate. What needs caution is that we do not overdrive these microphones (unless intended) as we might add noise from the preamp! That depends on the sensitivity of the microphone itself too as if it has low sensitivity and we need to push our preamp more than usual, then it is more likely that the added noise from the preamp will be audible in our recording. When it comes to dynamic microphones, Self Noise will be subject to the preamp only.

Signal to Noise in real life!

Now as you can imagine, the above describes an ideal situation with no external noises. What happens when we are using this microphone in the studio, or even live? We’ve got external noise that we need to deal with. Although the high SNR (Signal to Noise Ratio) and the low Self Noise our microphone offers already is great, we still need to consider how to limit the external noises.

These noises could be anything from interference, to other sound sources, environmental noise or maybe unwanted reflections from our own room.

Recording loud sound sources, such as a kick drum or a guitar amp at close proximity might save us from the trouble dealing with the external noises, but for other type of sources, like a cello for example, we will need to be more creative!

First action you would need to do, would be to move the microphone as close to the source as possible, but beware of the Proximity Effect!
Then make sure that the location you are recording is the best possible, away of room reflections and other sound sources. If there are reflections in that position, try to eliminate them if possible.
These first two steps, should help you enough so you don’t push the preamp that much. Therefore they will allow you to avoid any noise added to your signal by the preamp gain!
If possible, try to use a shockmount and if you do not need about recording the low frequencies of the source, make sure the low cut filter of your microphone is on.
Finally, as much as it is possible, try not to run signal cables along with power ones. Balanced cables should be fine for a few metres but if you can avoid it, why not?

You can find more about cables and their types in this article!

How do you feel about microphones now that we are getting deeper into their knowledge? Type your comments below and of course on our Instagram and Facebook pages!

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