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View Full Version : Preamp gain vs. fader level



yeahforbes
05-29-2008, 04:00 AM
Hi guys, this is one of my first posts here, so here goes. A buddy of mine who works with me on recording and live sound recently explained something I had never heard before, and frankly I don't believe him which is why I'm looking for more opinions.

He claims that there is a difference in what a microphone will pick up depending on if you adjust the gain knob at the top of the channel versus further down once it's at line level. He says, turning down the gain a little and bringing it back up at the fader (or makeup on an inserted compressor, for example) would reduce how far the mic picks up, and therefore would reduce feedback. Conversely, cranking the gain knob and reducing the fader would change the pickup (not polar pattern, but more distance related) so it "reaches out" more.

We both have a very clear understanding of gain structure regarding s/n ratio and distortion, and that's not at all the scope of this question. So basically, if I had a good signal at certain settings and then turned down the gain 6dB while raising it back up 6dB later on in the chain, would there be any difference (disregarding the change in noise floor)? No components being overdriven, etc.

The only related concept I can think of is that the load impedance on the mic changes when you adjust the gain, perhaps on only certain preamp designs. I've heard that if you use a split snake in a concert and the monitor engineer changes the gain, it can actually affect the level the FOH board gets and vice versa. But does it really change ANYTHING besides level??

Sorry for the long winded post... just trying to avoid the "not enough information" criticism that seems to be popular around here!

DAS
05-29-2008, 06:16 AM
It is conceivable that with the right combination of equipment the impedance/gain relationship between the preamp and mic could subtly change the behavior of the mic, or how the preamp/transformer,etc. reacts to signals coming in, but on any practical level with reasonably current equipment this issue is not on the table.

brianbfw
05-29-2008, 07:43 AM
sounds possible.

I mainly play classical guitar. my signal chain is an earthworks QTC40 with a Universal Audio 610. Usually i record everything 1st take, but when i do overdubs, and have the settings EXACTLY the same, there are slight tonal differences in the sound.

Alot of this has to do with the nature of the earthworks mic, move a mm and it changes the sound (stereo image). I've also heard room temp, humidity level, can affect tubes.

i'm not complaining, i have a great sound, but it used to drive my crazy trying to figure it out. now i just accept it.

Dave Burris
05-29-2008, 08:13 AM
I have seen this behavior in older boards and at very high system gains, but haven't really had to deal with it much for years. If pressed for an explanation I would have to speculate that something is funky in the design of the input stage of the channel, perhaps the input pad was not buffered and if causing impedance anomolies.

Mic selection and placement, EQ, and critical gain are more important factors.

yeahforbes
05-29-2008, 12:25 PM
Interesting stuff. We're working with a Yamaha MG24/14FX so I guess we wouldn't see it creep up on that board.