What is the difference between gain and volume?
April 16, 2015 10:47 PM   Subscribe

Like in a standard thingamabob such as the DJ-s use, for example. There is usually a volume knob and a gain knob. There is an absolutely clear audible difference between turning up gain and turning up volume. They are not the same at all. But what exactly is happening in the amplifier when I use one or the other? What do each of these things actually do?
posted by Pyrogenesis to Technology (12 answers total) 7 users marked this as a favorite
I can't speak that well DJ consoles. But on mixing consoles you usually have 2 amplifiers, a pre-amp that takes Mic level inputs and amplifies them to line level which is the level used through the board, eqs, effects etc. Once your sound is right your amplifier that takes line level inputs and pumps it to speakers. Generally gain adjusts the amplification of the pre-amp and the volume adjusts the volume to the speakers.

Adjusting gain is used a lot to adjust the tone or sound and can cause distortion or clipping, frequently intentionally. Its how guitar amps create distortion.

I think for DJs gain is used to adjust for differences in volume of the tracks being mixed.
posted by bitdamaged at 10:59 PM on April 16, 2015 [2 favorites]

bitdamaged said it well. However technically the terms gain and volume can be interchangeable. They both mean increasing (or decreasing) levels of power. While volume is usually reserved for audio, gain can be used for any form of amplification; audio, video, electrical, acoustic (sound waves in air), light, etc.

Gain can also be used to describe the overall increase/change in power, such as the expression "unity gain" which means no change - the level that went into the amp is the same as the level that comes out.

In tech terms, the low level inputs have a lower signal to noise (S/N) ratio than the outputs do. This is why we use shielded cables on inputs but not on the speaker outputs.

The lower the S/N ratio, the closer the signal (the music) is to the noise (the electrical interference of "the world"). Raising the signal level gain moves the music away from the noise level. Of course the noise level is also amplified so the less noise on the input the better.

So in short raise the gain as much as possible to get a higher input before raising the volume at the output. But as bitdamaged points out raise the gain to high and the input will clip.
posted by Zedcaster at 11:19 PM on April 16, 2015 [1 favorite]

The "Gain" knob on a channel of a DJ mixer like this controls the gain on the pre-amp input. If you turn it up too far you may hear distortion. The "Volume" fader is an attenuator, i.e. when all the way up it lets the signal pass through unchanged and as you move it down it fades the level down to eventually zero. DJ mixers normally have a cross-fader as well - a left-right volume-slider that gives an equal mix of the two channels in the center, all one or the other at the extremes.

There should actually not be much of an audible difference from tweaking the input gain vs the output fader on a channel, unless you are turning the gain up high enough to cause pre-amp distortion. Really you set the gain so that the level is right when that fader is all the way up, as it's the faders and the cross-fader that a DJ really works when doing something complicated, generally slamming a fader all the way up and down.
posted by w0mbat at 11:27 PM on April 16, 2015 [1 favorite]

I saw a good, if a little simplified, Youtube video about this a while ago, and it was still in my history:

5-minute Gain Structure Audio 101 Video by SynAudCon
posted by thelonius at 11:47 PM on April 16, 2015

However technically the terms gain and volume can be interchangeable.
No, not really. Technically speaking, gain is a ratio while volume is an absolute. You can have negative gain, but not negative volume…

That said, it doesn't help that both are often measured/specified in dB i.e. a dimensionless logarithmic ratio. Typically, the difference in practice is that gain (+ or -) is reported in comparison to the input level of whatever property you're measuring (e.g. voltage, power, etc), while audio volume implies comparing the measured value against a specific reference point (e.g. 20μPa - the standard threshold of human hearing - if you're reporting in dB SPL).

And that said, it is pretty common to interchange the two in layman's day-to-day usage.
posted by Pinback at 12:38 AM on April 17, 2015 [2 favorites]

Yeah, as others have touched on, least on a guitar amplifier, gain is what can push the amp into overdrive, which leads to often-pleasing distortion effects. That's a little different than what a DJ would likely ideally want to do, but that's how you use that knob if you're a guitar player, to adjust the level of snarl and bite in your amp's distortion. And yeah, it does affect the audible level of sound, too.
posted by limeonaire at 6:22 AM on April 17, 2015

But what exactly is happening in the amplifier when I use one or the other? What do each of these things actually do?

They both do the same thing - determine the level of signal (voltage) sent to a bit of circuitry (the core of which is most probably an operational amplifier (op amp)), which in turn raises the voltage/signal level (i.e. amplifies the signal) before the audio signal passes on to the next part of the mixer circuit. You're hearing differences between the two because of where they sit in the signal flow inside the DJ mixer and because each is designed to have a different level of gain within the overall mixer signal flow.

The "gain" knob is the first control, that sets how "hot" the signal is through the rest of the mixer. As zedcaster mentions, it determines the signal-to-noise ratio; and because the mixer has to be capable of handling a wide range of possible input levels, the circuit is designed to provide more level than the "volume" control later down the path. This also means that the perceived levels are not equivalent - halfway up on the gain knob will be "louder" than halfway up on the volume knob or fader.

The "volume" control sets the output level of the mixer to your amplifier and then your speakers, and since you've (hopefully) already set your internal mixer levels properly with the gain control, the volume knob doesn't need as wide a range of possible signal boost, so the circuit will have less "gain". At this point in the circuit, the DJ is just looking to make minor volume changes to balance the levels between two different songs, so they don't need as wide of an adjustment. Also, if the possible output level from this part of the circuit is relatively low, it can reduce the possibility of overdriving the amplifier and possibly blowing speakers (not that lots of DJ's won't try anyway . . . .)

The "Volume" fader is an attenuator, i.e. when all the way up it lets the signal pass through unchanged and as you move it down it fades the level down to eventually zero.

w0mbat makes a good point here, although it does depend on the manufacturer and model of DJ mixer - some mixers are designed so that the volume fader only reduces volume, but doesn't add any. IOW, there's no op amp circuit here, so "all the way up" on the volume just passes the signal directly through as if the volume control wasn't there.
posted by soundguy99 at 7:23 AM on April 17, 2015 [1 favorite]

Actually, more accurately, there may be an op amp circuit at the volume fader, but it's set to "unity gain", as in voltage in = voltage out, so in practice the volume fader is just an attenuator that can only reduce volume.
posted by soundguy99 at 7:29 AM on April 17, 2015

it is pretty common to interchange the two in layman's day-to-day usage.

My father the Electrical Engineer calls any audio volume control the gain. He'd be delighted to know DJ consoles actually use that label, Gain.
posted by Rash at 8:40 AM on April 17, 2015

Gain is for calibration, volume is for control.
posted by cogat at 10:23 AM on April 17, 2015

Awesome, thanks, I understand now. So the practical upshot is: first use gain to make things sound like you want them to, and then use volume for fine-tuning the final output.
posted by Pyrogenesis at 4:10 AM on April 18, 2015

More or less, yeah.

Although in the context of a DJ or other audio mixers, it's more like gain is for "setting the optimum input level without distorting" more than "sound like you want [it] to." IOW, if you're DJ'ing a set and the next track you cue up was recorded at a really low volume, you bump up the gain knob a little so it more closely matches the input level of your other tracks, so when you switch to that track you don't hear a volume drop, or at least not one you can't quickly solve with the output (volume) control.

Here's a "Setting Gain Structure" guide (pdf) from Mackie for a (hopefully) not too technical explanation of how to understand and set levels in an audio mixer & system.
posted by soundguy99 at 7:25 AM on April 18, 2015 [1 favorite]

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