Updated: Oct 7, 2019
A quick post today on something not particularly difficult or esoteric - but which seems to be a source of confusion to more than a few, especially when recording or mixing.
What's the difference about raising gain and raising volume?
The short answer is: none.
Both the gain knob and the volume knob (or fader) are there to take your signal and make it louder or quieter (technically, increase or reduce the amplitude of the waveform). Concretly this can be realized by using different types of electronic circuits (an amplification circuit, a fixed-attenuation circuit followed by an amplification circuit, etc) but that matters little.
So why having "gain" and "volume" as separate words?
Well, the difference is only about where this circuit is positioned in the signal chain, and what is its intended (or concrete) meaning.
If the circuit is there primarily to bring the signal up (or down) to a level that's easy to handle for other electronics which come after it, we talk about "gain"; if it's there to control the playback level of a speaker, we talk about "volume".
That means that controls early in the chain will most often called "gain" controls; and the last one in the chain (or supposed to be last) will be labeled "volume".
Controls intended to be in the middle of the chain.. we call what we want: oftentimes they'll be labeled "level", and that's it.
Some say that "gain" is about the input and "volume" about the output, but this idea does not stand to scrutiny: when we crank up the gain on a preamplifier, we aren't affecting the input (i.e. the mic signal, which stays just the same) but what is presented at its output. The signal gets louder because it's amplified. "gain" and "volume" are always about the output.
Another (equivalent) way of looking at it, is that
"gain" is about affecting the signal level as heard by components in the signal path;
while "volume" is about affecting it as heard by our ears.
Let's take a recording chain:
the first stage is the microphone. Inside the mic, there may be a little fixed-gain amplifier, meant to bring up to "mic level" the small voltage difference reported by the pressure sensor. The amount of amplification will be usually fixed (or be at most a couple of possibilities, if the mic has a pad). Since the point of the circuit is to amplify the signal so that the downstream circuit can handle it, we use the word "gain".
Same for the mic preamp: since its job is to bring the mic signal (aka voltage) up to line level (so that circuits downstream can work and be easier to build), the preamp knob is usually called "gain" as well.
Then we have some EQ, or insert effects - where level variations will be labeled as "level","gain","output" or really any word to that effect.
Finally, towards the end we will have the control(s) for playback: faders or volume knobs - and we use "volume" for them.
It's the same if we look at a mixer channel strip: the gain is usually the knob on top; and the channel has also a volume fader. Why "volume"? Well, the fader is meant to amplify or reduce the signal to sent to the main bus and therefore the speakers. That's the last stage in the chain, hence "volume".
But if you used the speaker stereo output to, say, drive an effect box (unusual but perfectly possible), the fader would be effectively a gain control, to determine the amplitude of the signal seen by the box.
The same goes for, say, a guitar amplifier: the preamp has a gain (or "drive") control to increase the small signal sent by the instrument (and often an EQ stage afterwards). The master volume is simply the gain stage driving the speaker.
That some amps have two "volume" controls in sequence is due to history: cranking the volume in a tube amp so that it exceeds the power amp performance envelope distorts the sound in a pleasing way (and changes the player's feel).
But it's ear-busting loud. So amp designers put another amplification stage after the original one - which becomes last in the chain and thus is labeled volume.
Since we guitarists are easily confused, the original "volume" labeling is sometimes left in place (some others replaced with "level" or similar neutral words).
In conclusion, "gain" and "volume" really are two different names for the same thing: signal signal level (amplitude) control.
What is important to understand is that every stage in a signal chain will affect the signal level - either increasing it or decreasing it a little.
Therefore, for every stage, you need to decide how you want to present the signal to the next. Each stage's input can only handle so much signal. So if you use the gain/volume controls to give the next stage more level that it can handle, this latter will produce a distorted signal, which will then carry on for the rest of the chain.
The process of taking these decisions is called gain staging.
Say you have a typical Mic -> Preamp -> Interface -> DAW chain.. if your mic is too "hot" for the preamp (which is unusual but may happen), the preamp will distort the signal.
If the preamp is set to too much gain for the interface to handle you will exceed its converters and get digital distortion.
And so on - up to the volume control: if your level is too much, the speakers themselves won't be able to handle it and they will distort (and break, if they don't have a built-in limiter).
So when you "gain stage", you are looking at the output level of every stage and making sure that it's in a range suitable by the next.
That's why most stage (preamps, effect boxes) have some form of meters - they allow you to see if you're inadvertently exceeding their signal-handling capability.
Worth also saying that a few times you will want to distort the signal. A classic example is a tube guitar amp, where the preamp section, or the power amp and the speaker cone, are pushed into distortion by exceeding the circuit design limits on purpose.
Another example is pushing a microphone preamplifier to obtain "coloration" (i.e. distortion).
Note that both cases, you need to reduce the level passed to the next stage: for example, with a guitar amp, you'll capture the sound by using a microphone of lower sensitivity (say a dynamic mic) and/or keep its preamplifier down, so that the next stage sees a signal at a reasonable level.
And with a mic preamp, you will need to be able to attenuate the signal after it's been distorted, but before it gets to the interface. That's why many preamps made for color have two gain controls - so you can crank up the first (and get color) but then reduce the level of the distorted signal to a point where it can handled by the next stage .
If you don't have meters, nothing to worry: your ears work just as well!