eli5 what does “gain” mean in regards to audio and recording?

Question

Basically just looking into external mics for my phone and all the reviews for the different products I’m looking at are talking about “too much gain” and “not enough gain” and I have no earthly idea what that means. I tried looking it up, but it’s confusing as hell for someone with no know, who just wants to record concerts to listen to again later

In: 26

Answer 1

An audio signal is just a measure of changes in air pressure. But there’s no real limit to how big those changes in air pressure can be. Imagine putting your ear or a microphone up against a nuclear bomb, for instance.

Similarly, when you try and take those pressure waves and convert them into a voltage that can be processed electronically, the voltage that you would get from a (presumably indestructible) microphone capable of picking up the sound of a nuclear blast would likely be in the millions of volts. Any audio engineer trying to deal with a signal like that would find themselves electrocuted to a crisp trying.

So when we try and measure or record an audio signal, we have to deal with the practical reality around the range of voltages we can meaningfully process. A typical microphone will convert sound waves from speech into voltage waves of around 1-100 millivolts.

But you’ll want to use microphones to pick up different kinds of sounds. For instance, you might in one setting want to hear two people whispering, and then in another setting you’ll want to capture a gunfight. If you were to just record the raw voltages coming out of the microphone for each of these situations, you might find the whispers are too quiet to do anything useful with, and the gunshots are so loud that the sound waves push the microphone outside the voltage range it’s allowed to produce, resulting in “clipping”.

You can fix this electronically by scaling the voltage up or down so that both the whisper and the gunfight both end up producing similar voltage ranges. This maximizes the fidelity of the sound captured, so that a whispered conversation can be intelligible and the gunfight captures the full range of sounds.

This factor that you apply to the voltage in order to scale it like this is called gain.

There’s also a digital version of this. Once voltages are processed by a computer, they’re just turned into numbers. But in a computer, numbers have a fixed degree of precision, and often range. So a mathematical scaling can be used to add or remove gain once it’s in the digital form as well.