Impedance/level-matching issues

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pricklyrobot
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Impedance/level-matching issues

Post by pricklyrobot » Sat Apr 24, 2010 10:25 pm

I've researched this myself, and I think I may have it nearly right, just looking for confirmation (and/or correction) of the following rules of thumb:

Guitar Level = Hi-Z, low dB
Mic Level = Lo-Z, Low dB
Line Level = Hi-Z, High dB

DI Box: converts Guitar Level to Mic Level
Re-Amp Box: coverts Line Level to Guitar Level

Trying to figure out the best way to hook up my new patchbay (to allow for using guitar pedals with synths and such), and all this stuff is starting to make my head hurt.;)
Arturia MiniBrute -- bits o' Euro -- Sammich SID -- E-mu MP-7 -- Korg ER-1 -- Thingamagoop

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pricklyrobot
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Re: Impedance/level-matching issues

Post by pricklyrobot » Sun Apr 25, 2010 1:41 am

Actually, it seems I got one of those wrong. It should be:

Line Level = Lo-Z, High dB

I think? :facepalm: Trying to do things the right way is hard.
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stillearning
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Re: Impedance/level-matching issues

Post by stillearning » Mon Apr 26, 2010 4:08 pm

pricklyrobot wrote: DI Box: converts Guitar Level to Mic Level
Guitar level and mic level are roughly the same. DI boxes can have multiple uses, but generally I've seen them used to convert unbalanced signals into balanced signals to be able to the travel long distances from stage to FOH with minimal noise pick-up. They can also be used to drop line level or even speaker level to low (mic) level, I believe. Many also have built-in ground lift switches to help eliminate ground loops. Sort of Swiss army knives in live sound situations.
As always, kindly allow for the possibility I have no idea what I'm talking about.

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Re: Impedance/level-matching issues

Post by Stab Frenzy » Mon Apr 26, 2010 11:37 pm

Also active DIs will increase the current to help drive the signal over the longer distance. That's why active DIs sound better on instruments with passive pickups.

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pricklyrobot
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Re: Impedance/level-matching issues

Post by pricklyrobot » Tue Apr 27, 2010 12:00 am

stillearning wrote:
pricklyrobot wrote: DI Box: converts Guitar Level to Mic Level
Guitar level and mic level are roughly the same.
Poor choice of words on my part, as the dB level is in the same range and it's just the impedance that the DI box is coverting. Perhaps I should have done my little chart thus:

Guitar Signal= Hi-Z, low dB
Mic Signal = Lo-Z, Low dB
Line Signal = Lo-Z, High dB

DI Box: converts Guitar Signal to Mic Signal
Re-Amp Box: coverts Line Signal to Guitar Signal

I'm mainly looking at using DI's/Re-Amps in a studio setting, for interfacing synths and guitar pedals, or for using guitars with line-level effects.

I initially ran into to trouble with the following set-up: synth plugged in mixer Line Input 1 (which features an FX Insert Channel) -> send of FX Insert Channel going to Re-Amp box -> Re-amp into guitar fuzz pedal -> fuzz pedal out into DI box -> DI box back into return of FX Insert Channel.

I realized that I was getting the impedances matched correctly, but the Mic Signal coming out of the DI box was going back into a Line Signal input on the mixer (so the dB levels were still mismatched). When I plugged the output of the DI into a separate Mic Input on the mixer, then I seemed to be getting a decent sound at a usable dB level.
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electro funker
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Re: Impedance/level-matching issues

Post by electro funker » Tue Apr 27, 2010 8:20 pm

remember to groundlift your guitar amp and synth´s etc. if your mixer is grounded, so only one ground is found in your system :)

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