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Need Help With Impedance.
Old 28th July 2008
  #1
Lives for gear
 

Need Help With Impedance.

Ok, I am just trying to wrap my head around some stuff here..

So when recording a guitar/bass into a computer, you must have a D.I. because: the output of a guitar is:
A) Guitar = Low Level, High Impedance
B) Mic Preamp wants to receive High Level, Low Impedance

if you feed a low level signal into the mic preamp, it won't be enough to drive the preamp, and on top of that, the preamp wont load the guitar and so its won't sound good due to multiple "failures". Is this correct?

So, you get a DI box to convert the Low Level, High Impedance guitar signal into a High level, Low Impedance one for the Mic pre, then it goes into the recorder/computer.

Now- when the signal comes out of the line out from the computers interface, it's line level (which is a high level, right? but what impedance?) and if you want to Reamp a track into a guitar amp, (which is expecting a low level, high impedance signal) you need to use a reamp box to knock the level from high down to low (and possibly perform impedance correction?).

now, say you wanted to record a DI track of guitar and run it back out, then back through the mic pre over and over (experimentation):
Gtr>DIbox>Preamp>Computer>Reampbox>DIbox>Preamp>Computer>Reamp>DIbox>Preamp>Computer etc?

I thought this might be interesting, because, after multiple passes, wouldnt the particular character of a given preamp exponentially build on itself? say the preamp boosts mids, upon each pass, the mids will be boosted, then those boosted mids will get boosted again, over and over, etc, right?

just curious..

Do I understand how all of this works, though?
Old 28th July 2008
  #2
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danbronson's Avatar
Well, not just the character of the preamp, but everything in the chain will build upon itself if you do that. Could be interesting.

I'm not sure of the details, but I know that there are three basic levels:
-instrument (though active and passive pickups will yield different levels, should be the same impedance I believe?)
-microphone (obviously dynamics put out less level than condensers, and mic impedance ranges a bit)
-line level (there's consumer and professional levels, -10 and +4 respectively I believe, as well as others that aren't very common)

Maybe someone could shed some more light on this and go into depth. Feel free to correct anything I'm wrong about, I'd appreciate it!
Old 28th July 2008
  #3


Ok - let's get a few things straight.

A mic pre-amp wants to amplify a low-impedance, low-level signal.

This pre-amp has a fairly low input impedance, which will "load" the pick-up of a guitar too much (with loads, the low impeadance is a "heavier" load).





-tINY

Old 28th July 2008
  #4
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Quote:
Originally Posted by DarkEcho View Post

Now- when the signal comes out of the line out from the computers interface, it's line level (which is a high level, right? but what impedance?) and if you want to Reamp a track into a guitar amp, (which is expecting a low level, high impedance signal) you need to use a reamp box to knock the level from high down to low (and possibly perform impedance correction?).
The output impedance of a typical modern line level device is 50 to 100 ohm unbalanced and 100 to 200 ohm for balanced connection.

High level? Uhm, could be. When digital is maxed it's called 0dBFS and that use to equal 2V to 7V depending on the gear and if the nominal level is -10dBV or +4dBu.

So yes, typically high level compared to a non amplified pup or mic signal.


/Peter
Old 28th July 2008
  #5
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w_stylz's Avatar
Provided that you figure out a way to run the same signal out of a preamp, into a computer back out through a reamp box and back into the same preamp (which would be impossible without a combiner / mixer) you will have succeeded in creating a nasty feedback loop. This happens when you feed something back into itself in a looping manner. This technique was used back in the day to get a certain presence in broadcast applications with the amount of signal feeding back kept at a low level to keep the loop from damaging the equipment. In any case, whatever you are trying to accomplish can be done with basic plug in effects so I wouldn't risk destroying your speakers and ears to do this.

The whole point of reamping is to use different guitar amps on the same guitar performance so that you are not stuck with the guitar sound that you recorded in case it doesn't work in the mix.


Quote:
Originally Posted by DarkEcho View Post
Ok, I am just trying to wrap my head around some stuff here..

So when recording a guitar/bass into a computer, you must have a D.I. because: the output of a guitar is:
A) Guitar = Low Level, High Impedance
B) Mic Preamp wants to receive High Level, Low Impedance

if you feed a low level signal into the mic preamp, it won't be enough to drive the preamp, and on top of that, the preamp wont load the guitar and so its won't sound good due to multiple "failures". Is this correct?

So, you get a DI box to convert the Low Level, High Impedance guitar signal into a High level, Low Impedance one for the Mic pre, then it goes into the recorder/computer.

Now- when the signal comes out of the line out from the computers interface, it's line level (which is a high level, right? but what impedance?) and if you want to Reamp a track into a guitar amp, (which is expecting a low level, high impedance signal) you need to use a reamp box to knock the level from high down to low (and possibly perform impedance correction?).

now, say you wanted to record a DI track of guitar and run it back out, then back through the mic pre over and over (experimentation):
Gtr>DIbox>Preamp>Computer>Reampbox>DIbox>Preamp>Computer>Reamp>DIbox>Preamp>Computer etc?

I thought this might be interesting, because, after multiple passes, wouldnt the particular character of a given preamp exponentially build on itself? say the preamp boosts mids, upon each pass, the mids will be boosted, then those boosted mids will get boosted again, over and over, etc, right?

just curious..

Do I understand how all of this works, though?
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