Contolling feedback: Are gain vs. volume adjustments equivalent?

[wcap]

Here is perhaps a naive question (which I could probably answer by more trial and error):

When trying to control feedback, sometimes one reduces the gain (e.g. on your mixer).

Does reducing volume (on your mixer, either for that particular channel, or your master volume) have the same effect on feedback control as reducing gain?

Why or why not?

[sdelsolray]

Originally Posted by wcap

Here is perhaps a naive question (which I could probably answer by more trial and error):

When trying to control feedback, sometimes one reduces the gain (e.g. on your mixer).

Does reducing volume (on your mixer, either for that particular channel, or your master volume) have the same effect on feedback control as reducing gain?

Why or why not?

"Gain" and "volume" are two terms that can have different meanings or the same meaning, depending on the context. When discussing feedback, they essentially have the same meaning.

[jseth]

William;

Gain setting is extremely critical for certain devices, like an acoustic guitar pickup system, for instance...

Google "gain staging" or hit the link on the Bose User's Forum and study that, if you have not yet done so. VERY informative and helpful, whether using Bose gear or not.

Technically speaking, you "can" reduce either gain, channel volume or main output volume to reduce feedback, BUT the trick is to have everything "working" at an optimum level.

My Baggs Anthem SL pickup, for example, sounds REALLY bad whenthe gain is not adjusted, when compared to having a proper gain setting for that pickup. I don't know what happens, electronically speaking, but the tone becomes thin, wimpy, lifeless... and it doesn't matter how much you turn up the volume, it still sounds that way, only louder!

I guess what I'm trying to say is that, while you "can" use the gain control to reduce volume, in many cases, you SHOULD NOT, not if you want the "best' sound from your gear...

[simondylan]

Originally Posted by jseth

William;

Gain setting is extremely critical for certain devices, like an acoustic guitar pickup system, for instance...

Google "gain staging" or hit the link on the Bose User's Forum and study that, if you have not yet done so. VERY informative and helpful, whether using Bose gear or not.

Technically speaking, you "can" reduce either gain, channel volume or main output volume to reduce feedback, BUT the trick is to have everything "working" at an optimum level.

My Baggs Anthem SL pickup, for example, sounds REALLY bad whenthe gain is not adjusted, when compared to having a proper gain setting for that pickup. I don't know what happens, electronically speaking, but the tone becomes thin, wimpy, lifeless... and it doesn't matter how much you turn up the volume, it still sounds that way, only louder!

I guess what I'm trying to say is that, while you "can" use the gain control to reduce volume, in many cases, you SHOULD NOT, not if you want the "best' sound from your gear...

jseth is absolutely right! The reason why though is because "gain" happens at the beginning, or the input stage of the circuit in the preamp. Volume happens at the end once the signal has been altered or processed by the circuit. Your signal needs to have the appropriate amount of gain going in, to get the most out of the circuit. Without the right gain setting your tone will suffer, as he stated it does.
Now for fighting feedback, you should never need to adjust either gain or volume to try to combat feedback! EQ, notch, & phase. Get those right and you won't have any problems with it.

[rschultz]

They are different. Years ago I simply thought gain was course and volume was fine… but that's not right. Yes they are interchangeable in terms of volume, but not feedback. One trick to try for reducing feedback is to lower the gain… then bump the volume up a bit to get the volume back. But as mentioned, feedback is more a function of speaker placement and EQ. As a sound guy, you usually can't move speakers around during a performance and sometimes you don't have time to EQ… so lowering the gain is the best option. Yes you want the gain as high as possible for best tone, but you have to balance that with feedback headroom.

[coconuts]

Originally Posted by rschultz

But as mentioned, feedback is more a function of speaker placement and EQ. As a sound guy, you usually can't move speakers around during a performance and sometimes you don't have time to EQ… so lowering the gain is the best option. Yes you want the gain as high as possible for best tone, but you have to balance that with feedback headroom.

This is why notch filters (basically parametric eqs) are really a good thing to have and are now found in many acoustic amps and DIs for acoustic instruments.

[wcap]

Thanks everyone for your responses. I'll reply with a better response soon when I have a bit more time.

[pieterh]

Gain can be thought of as the (active) volume for the instrument at the point of entry to the amp or mixer etc. Volume can be thought of as a (passive) fader (whether a fader strip on a mixer or pot on an amp) which adjusts how much of the original signal gets through to the speaker. It isn't quite as simple as that but as a working method it should help.

Having the right gain is live sound 101. Think of all the little bits of noise created in the signal chain, starting from the pickup system itself. If using an active system then that needs to be optimised so that the guitar is sending a signal with the best possible signal-to-noise ratio, and similarly along the signal chain. Anywhere where the s/n ratio isn't at its best there is a risk that bringing up the level later to compensate will also raise the noise floor. And noise can and will contain frequencies that will come through the PA or monitors and contribute to agitating the guitar into feedback.

Pulling down faders (volume) to cure feedback is necessary to protect your ears but should be seen as a band-aid to stop the bleeding while you search for what was causing the feedback and then stitching the wound by fixing gain structure, speaker placement and front-of-house and monitor volumes.

[dberkowitz]

Perhaps this will help. In audio we talk about gain structure. It is how you use each stage of the signal path so you do not overdrive the output (Mains or monitors) and cause either distortion or feedback. Setting the gain structure properly will give you the headroom and lessen the probability of distortion and feedback. It won't prevent feedback, but it's part of the picture.

On a mixer an input comes in through a channel strip which includes an input gain knob, EQ, and depending on the mixer, several other things, and the fader -- the linear slider that also controls volume levels.

The input gain actually controls what we call the "head amp," and thus how much you are amplifying the signal coming in from a microphone, instrument, or anything else you want in your mix. There is one on every input channel. The fader on the other hand, while controlling levels, is only an attenuator. When the fader is at 0, it is neither adding or subtracting. Pulling the fader down merely attenuates the signal coming from the head amp. Ideally, the input gain is set at a place where the incoming signal sounds full, has enough level, and is not distorting.

We also talk about gain-before-feedback, i.e., how loud we can make a mic or acoustic pickup before it causes feedback. The feedback is controlled through EQ, be it parametric on the channel strip, graphic or parametric on the outputs, and notch filters usually at the source (although on better consoles, one can dial a parametric filter that is a notch filter (which is simply a parametric filter with a very narrow band or Q)). Feedback also is controlled by volume. At a certain point you've pulled down as many frequencies as you can and doing anything more is simply hacking the signal and it's self defeating in terms of fidelity and you usually don't get much more volume.

[Andy Howell]

Originally Posted by dberkowitz

Perhaps this will help. In audio we talk about gain structure. It is how you use each stage of the signal path so you do not overdrive the output (Mains or monitors) and cause either distortion or feedback. Setting the gain structure properly will give you the headroom and lessen the probability of distortion and feedback. It won't prevent feedback, but it's part of the picture.

On a mixer an input comes in through a channel strip which includes an input gain knob, EQ, and depending on the mixer, several other things, and the fader -- the linear slider that also controls volume levels.

The input gain actually controls what we call the "head amp," and thus how much you are amplifying the signal coming in from a microphone, instrument, or anything else you want in your mix. There is one on every input channel. The fader on the other hand, while controlling levels, is only an attenuator. When the fader is at 0, it is neither adding or subtracting. Pulling the fader down merely attenuates the signal coming from the head amp. Ideally, the input gain is set at a place where the incoming signal sounds full, has enough level, and is not distorting.

We also talk about gain-before-feedback, i.e., how loud we can make a mic or acoustic pickup before it causes feedback. The feedback is controlled through EQ, be it parametric on the channel strip, graphic or parametric on the outputs, and notch filters usually at the source (although on better consoles, one can dial a parametric filter that is a notch filter (which is simply a parametric filter with a very narrow band or Q)). Feedback also is controlled by volume. At a certain point you've pulled down as many frequencies as you can and doing anything more is simply hacking the signal and it's self defeating in terms of fidelity and you usually don't get much more volume.

That does help but I like to think in more simpler terms.

Gain for me is what the mixer/PA takes in. I tend to adjust my pre amp to show out a signal at about 60% — I can go about this but at 60% it all seems clear and well defined. In the mixer mater volume can happily he controlled with the confidence is knowing that the signal it is receiving is clean and non distorted.

[Doug Michaels]

I am no techie for sure. But this is what I do in mixing my sound using a mixer, a lot of effects on a pedal board, a good Shertler Jam 400 or Fishman SA 220 as the final stop in the chain.
When setting my sound, I start with the gain and set is as high as it will go without feeding back. My volume slider for each channel is at zero and this is important.
When the gain is set so that there is no feedback or distortion in my speakers, I then bring up the channel volume to where I want it. Its also important to not set the overall main volume too high to start with or it will hinder setting the gainfor each channel as high as possible. So keep the main volume low.
As already stared in this thread, the eq is also very important in getting that gain up there. If you hear high frequency feedback while turning up the gain, then lower the eq for the high frequencies first rather than just turning down the gain. The eq and the gain control work as partners but its up to you to be sure they get along well. And as already said, moving the speakers a little can make a big difference in eliminating feedback. Hope all this helps from a guy who has gigged for thirty years but has no idea how all this truly works.