Gain and volume are often used but, seldom understood.
You probably use gain all the time without knowing exactly what it is or how it might be different than volume.
And you're not at all alone.
There are guitarists spanning all styles and skill levels that use gain without really knowing what it does.
What's going on with gain and volume? | Flickr Commons Image via Keeeegan
For a long time, that was me.
I knew gain created more distortion and in some situations seemed to act more like an additional volume knob. It wasn't that I was completely wrong but, I certainly didn't understand the background story.
Moreover, I just thought that volume and gain were, more or less, the same.
Are volume and gain the same thing?
My tendency to lump volume and gain into the same definition was an intellectual mistake, and a lazy one at that.
Because, while they can both incur volume, gain cannot be defined the same way you would define volume.
Which is which?
They serve two different purposes.
In the Modern Dictionary of Electronics, Rudolf F. Graf defines gain as the following:
Any increase in power when a signal is transmitted from one point to another, usually expressed in decibels or, any increase in the strength of an electrical signal, as takes place in an amplifier.
He also gives us a standardized definition of volume:
The term volume is used loosely to signify either the intensity of a sound or the magnitude of an audio frequency wave.
This is why you often have both a GAIN and MASTER VOLUME knob on an amplifier. The key to understanding the difference between gain and volume is found in understanding the functionality of those two knobs, in the context of the definitions we've just read.
Let's start with the GAIN knob:
Understanding the gain knob
To understand what a gain knob does we need to understand the basic two-part structure of a guitar amplifier.
I'm sure you've noticed that most amplifiers have a standalone GAIN knob, like the one pictured below:. In the Marshall amp pictures there are two channels, though note that the gain knob for channel B is missing.
Normally, you'd have one gain knob per channel:
A shot at the GAIN knob on a Marshall JCM 900. | Flickr Commons Image via Roadside Guitars
When you guitar's signal gets to an amp, there are two stages it needs to go through before it's output through a speaker:
- Preamp Stage
- Power Amp Stage
What most people miss is that the GAIN knob only functions in the preamp stage.
Gain is the volume control that amplifies the signal going into the preamp, hence you see that the gain knob on the Marshall JCM 900 (above) is labeled "PREAMP" on both channels.
The preamp stage of an amplifier and gain go hand in hand.
Your guitar's signal goes first into a preamp. Gain controls the volume at this stage of amplification.
Preamplifier.org defines preamps in the following manner:
A preamplifier is required to amplify a signal, when the source level is too low and has to be pre-amplified in order to be usable for further processing, control or any other use.
Thus the preamp is where the signal is essentially prepped and shaped for final output.
It's also where all EQ measures are applied. Bass, mid and treble are all functionality that get adjusted and implemented in the preamp stage.
In other words, the actual amplification of your guitar's signal takes place in the preamp.
Understanding the volume knob
After the preamp, your guitar's signal gets moved to the power amp, where it's output through the amp's speaker or an external speaker cabinet. At this stage, the knob labeled VOLUME or MASTER VOLUME is what controls how loud the output is.
Turning gain up at the preamp stage and either keeping master volume the same or lowering it, at the power amp stage, is how you get a distorted signal.
Gain is applied at the preamp stage while volume is applied at the power amp stage.
In most cases, the preamp and power amp are the same unit, as you would see in most guitar combo amps or amp heads.
Additional preamps are often added via a pedal or rack effects unit.
A look at the VOLUME knob on a Marshall JCM 900. | Flickr Commons Image via Roadside Guitars
We see right above the volume knob the MASTER label, indicating it's controlling the master volume of the power amp after the preamp has already done its work.
The higher the gain, the more we're overloading the preamp, thus creating the fuzz or distortion that you hear.
This is why gain knobs can also be referred to as the following:
- Channel Volume
How a pedal preamp works
Gain is also what you're utilizing when you put a preamp at the beginning of your pedal chain, which is why many preamp pedals are simply called "boosts" or "booster pedals."
Take the EHX Linear Power Booster for example:
The EHX Linear Power Booster is basically an extra gain knob, boosting the signal going as a standalone preamp. | Flickr Commons Image via Kuyabic
It only has one knob labeled BOOST.
That knob functions the same as the gain knob on an amplifier, in that it takes the signal from your guitar, increases the volume then sends the boosted signal on it's way the final volume adjustment.
Again, you get distortion when the gain goes up and the master volume either comes down or remains stagnant.
Preamps can have other functionality as well, like basic EQ or even effects, which we see on the amplifiers in the form of a three-band EQ, presence, reverb controls and sometimes more.
Gain is as much a part of shaping your tone as the BASS and TREBLE knobs.
The master volume doesn't have any say until after the preamp has done its work.
Other resources on gain and volume
Here are a few resources I'd recommend for continued reading on the differences between gain and volume:
- Jeff Owens' article on Fender's Website: What's the difference between gain & volume?
- SonicBids Blog: The Critical Difference Between Gain & Volume Explained
- OffBeatBand.com: The Difference Between Gain, Volume, Level & Loudness
You can drill down into this topic a lot more if you start to consider aspects of amplification and audio engineering that aren't strictly limited to your guitar amp.
For our purposes, knowing how gain impacts the preamp and how volume impacts the power amp is enough to know how to properly utilize whatever guitar gear you might be sporting.
Once you understand the difference between gain and volume, your amp dials will start to make a lot more sense.
Have questions about what we cover in this post?
You can shoot me an email if you want.