biguana - 15 February 2010 02:12 PM
Can someone explain to me the relationship between these things?
I recently got a Digitech Quad 4 (£54 off eBay :o) thanks John and S-E-A!)
What's my commission?
I'm going to put two direct outs from my td-8, one out from my SPD-S and I hope a mic signal from miked acoustic hats (via a stand-alone mic preamp) through it, so I can unify everything in one box and process it together before it goes to the desk via DIs (a multi-channel DI box when I can afford it).
Sounds like a plan..
Now I've asked my bandmates exactly what preamps are for and no one actually knows.
What I have pieced together so far:
I notice our two-channel DI box has 'hi' and 'lo' written by the inputs and outputs.
Working blind here, but suspect it's connected to level matching, lo for small level signals (guitars), hi for line level signals. Why these would be on the outs too, not sure, unless it's to match the output to the desk that expects a microphone level signal.
I know line level signals are 'higher' than mic level ones.
You've gained a silver star..
I know you need DIs between line-level outputs and the desk but not between mics and the desk.
You've earned a gold star...
I know you need to preamp a mic level signal before it goes into a 'normal' (i.e. usually intended for guitar/keyboards) effects processor, but not a line level one.
Well sort off, a microphone pre-amp will take the small signals from a microphone to a 'line' level. However, guitars too work on low level signals, and tend to be high impedance, so you can find guitar pre-amps too. Guitar effects pedals would expect to 'see' a guitar type of input. The guitar amplifier pre-amps the signal, and then amplifies that signal to one to drive the speaker.
I know a DI box converts high impedance signals to low impedance ones.
Another gold star...
...so does this mean a preamp is essentially a DI box in reverse?
Not really..
I know you can use the ART Tube MP as a DI box - is the 'phase reversal switch' for reversing it in some way?
Flips the phase of the signal 180'. Think of the sound waveform as a sin wave going up and down. Reversing the phase it would be down then up.
As a drummer you will know that sometimes the snare is mic'ed from above, and below.
The bottom mic would need it's phase to be reversed as it would effectively be out of phase with top mic. If the bottom mic phase reversed the signals add together.
Is a line level signal higher impedance than a mic one, or higher something else?
Sometimes...
When something is described as high impedance (hi Z) it's normally 10K ohms and above. Cheap microphones that come with cassette recorders (remember them) would be hi=Z. Guitars are hi Z.
Balanced microphones impedance tends to be around 600 ohms.
Line level outs on keyboards, can be anything around 1K.
Here's what wikipedeia has to say on impedence:
http://en.wikipedia.org/wiki/Impedances
Understand it? No me neither..
I treat impedance has and AC equivalent to DC resistance.
If you plug a guitar into a XLR, it will sound dull, with a loss of high frequencies.
It's down to loading apparently..
Plug a synth into a XLR, probably be ok, although it will be a 'hot' signal.
And I know pre-amps and DIs both have a role in improving the sound quality, adding warmth, fatness etc - how important is this quality control area? What other quality control areas/variables are there to consider?
A DI box is really just a level matching, & impedance matching device.
Some pre-amps can be described as you say, especially when they are equipped with valves.
In terms of quality variables, well decent cables are important.
A £40 pre-amp might not be in the same league as a Avalon AD2022.
Thanks
Don't clap - throw money..
