Feedback prevention trick:Myth or Fact (live sound question)

[Gentleman Jim]

I've read all of the posts in this thread, and I've followed about half of what's been said. So much of what has been put forth here is hypothetical and speculative that it's nearly useless.

There would be engineering differences between the circuitry of the gain stage and the circuitry of the fader stage, right? So that would indicate that there would be some slight differences between boosting one 6 dB and cutting the other, versus cutting one and boosting the other. Would it be an appreciable difference? It probably depends on many factors, not the least of which is: what board are you talking about?

Ultimately, I'm more of a sound realist than a sound theorist. I know that certain factors will affect the way sound travels, such as humidity, temperature, and altitude. I know that the singer's mic technique will play a much bigger role in the possible incidence of feedback than which resistor was used in the output stage fader of the soundboard. So I deal with the larger factors first; namely mic choice, reasonable gain staging, and doing my best to make the musicians aware that their stage volume is an integral part of the overall sound.

I've never mixed monitors in a university acoustical laboratory or an anechoic chamber, so I can't get too caught up in the absolutes that are being thrown around. What I've picked up from ~15 years of mixing monitors and FOH is that you can guarantee that something will change between sound check and the performance. It might be that the venue becomes much hotter and sweatier, or that the singer will suddenly start belting out when she was a timid church mouse before, or that the bassist will just turn up from 2 to 4... on an SVT... in a 150 capacity club. But something will change; and when it does you can use all your scientific knowledge to help address the new challenge, but if there's one other person in the place who cares that you've summoned up your learning on the Haas Effect to decide how long the pre-delay on the snare reverb should be, that's an unusual night.

[chconnor]

Totally fair enough, Gentleman Jim, it's definitely gone pedantic at this point. My motive is to really put the theory to rest (if indeed it should be at rest) so i can know not to spend any energy on the unimportant stuff when mixing and so i can confidently fend off pressure to use this trick. In other words, for me, the answer to "what board are you talking about" is "any board in common use for live sound". I'm feeling like there is no use for the trick (sounds to me that the differences between gain-knob-gain and fader-gain fall into the "not relevant to feedback prevention on any conventional board" category), and i'm inviting demonstrations or explanations to the contrary.

-c

[Snarl 12/8]

It's been my experience that gain knobs tend to add more distortion to a signal as they are cranked than faders do. On most boards. This goes back to someone's comment about using the "best" gain stage (faders) to do the critical adjustments.

Doesn't distortion on a signal cause it to feedback more? Since you're introducing harmonics, extra frequencies, with feedback potential?

Like, if I want my guitar to feedback at a given volume, I'll crank the "gain" and lower the master volume as my first step. Then I'll start placing myself inappropriately close to my amp, introduce a distortion pedal, etc., etc.

I'm not trying to be pedantic. I just, in my gut, believe there might be something to this theory, and I'm asking this as a question for the more knowledgeable folks.

I do fear that the "more knowledgeable" folks seem to have a "more closeder" mind sometimes. And tend to discount theories out of hand if they haven't heard about them in their 10-30 years or experience.

[thethingwiththestuff]

If you're working live in a club sending monitors from the FOH consolse, you have one input gain that better be loud enough for both the monitor send and the main mix. once it's set after check you can't touch it.

there are a lot of choices you just don't have in a live situation. damn the distortion, why's the board distorting on a simple vocal into a 58?

[thethingwiththestuff]

Like, if I want my guitar to feedback at a given volume, I'll crank the "gain" and lower the master volume as my first step. Then I'll start placing myself inappropriately close to my amp, introduce a distortion pedal, etc., etc.

whoa, wait, a mic preamp is nothing like a high gain guitar preamp! guitar amps are designed to clip pleasingly, mic pres on live consoles are def. not...

[Gentleman Jim]

It's been my experience that gain knobs tend to add more distortion to a signal as they are cranked than faders do. On most boards. This goes back to someone's comment about using the "best" gain stage (faders) to do the critical adjustments.

Also, there's the important difference that gain knobs tend to be smallish in size and linear in their effect; the first quarter turn adds as much gain as the last quarter turn. On the other hand, faders tend to be a bit larger and are typically logarithmic in their effect; the first quarter gets you from ∞ to -30 dB, then the next quarter gets you to -10 dB, then the next quarter to unity, then up to +10 dB. (more or less)

So a gain knob, by design, is a less precise controller than most faders. This in addition to any other differences in engineering.

[thethingwiththestuff]

So a gain knob, by design, is a less precise controller than most faders. This in addition to any other differences in engineering.

yep.

[ashcat_lt]

I'm pretty sure this is a Myth as stated in the OP. Just doesn't make any sense, for the reasons mentioned above. -6db + 6db = 0 and you're right back where you started.

I can't believe that most modern mic pres are designed in such a way that their gain control makes any significant difference in the sensitivity or frequency response of the microphone itself. Seems like that would be considered by most to be a serious design flaw! And anyway, if mic sensitivity decreases, it means you'll just be turning it up even more to get the desired level out of the vocalist, and a good monitor level, which puts you right back where you started again.

Distortion helps create feedback mostly because of its compression/limiting action. The quieter sounds are louder in relation to the "program material", so it's more likely to break loose.

[Scodiddly]

Not to mention that impedance changes in the mic input wouldn't affect a condensor mic. It's already going to have an impedance buffer built in, wouldn't work without one.

C'mon, folks. If this actually worked, somebody would have built and marketed a box to take advantage of it already.

[JohnDavisNYC]

yay! can we finally put this BS to bed?

john

[chconnor]

yay! can we finally put this BS to bed?

:-)

OP is satisfied, unless any technical explanations or test results are posted...

-c

[Jay Reynolds]

Trust your ears, not something you read on the Internet.

Microphones are not intelligent lifeforms

Two...two...TWO sig-worthy posts in one thread. You, sir, are an artist

[Scodiddly]

Trust your ears, not something you read on the Internet.

Microphones are not intelligent lifeforms

Two...two...TWO sig-worthy posts in one thread. You, sir, are an artist

Meh. I would have put my money on "If this actually worked, somebody would have built and marketed a box to take advantage of it already."

[accordion squeezist]

You remember the Tapco boards? Gain & fader all under one cool oil-filled pot.

[casey campbell]

set the console at unity gain.

if you have feedback issues you can do the following:

1. change the monitor or mic position where the wedge is firing into the null of the mic. if it's a cardioid, either at the 11 or 1 o'clock position relative to the microphone.
2. get there early and ring everything out....find out your offending freqs. and make your eq adjustments from there.
3. sometimes the polarity switch can make a difference.
4. have the right tools for the job (i.e. - eq for every monitor channel).

also, if you mix with the gains, i would imagine you'd drive the performers crazy with ever-changing monitor levels (unless you split and have your own monitor guy). set the console to unity, mix volumes with your faders.