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View Full Version : Questions for all of the audio experts out there



Eric
December 11th, 2009, 01:16 PM
WARNING: I am laying out all of my ignorance below and asking every question that came to mind in writing this. It will be a bit like drinking from a firehose, but please bear with me and answer if you're willing.

I've been reading up on impedance a bit lately and have several questions:


I think that you need a DI box for acoustic guitar (or electric) to bring it from instrument (IIRC, -60dB -- is that right?) to line level (-10 dB), but I have heard that it is possible to plug a bass directly into the snake and get sound out through the monitors/mains. Why is this? Is a bass signal a different impedance? Does it have to do with active pickups? Isn't there a preamp in most acoustic guitars anyway? Shouldn't this put the output at line level? How does a DI box work anyway? Why are electric guitars so quiet when you put them through a DI box? I've tried it before just to see, but the results blew.

If mics are also at a similar level to instrument pickups (http://en.wikipedia.org/wiki/Line_level#Line_level_in_traditional_signal_paths) , why can they plug into a snake directly without a DI box? Don't they usually get routed through a preamp? Why don't guitars get the same path?

Could you, in theory, go from a guitar to a single stompbox to a snake and still get a reasonable level of signal into the board? I always thought the output of most pedals was a line level signal, so it effectively acts as your preamp.

I've read that headphones generally have lower impedance than line level. Is there a reason why you can't go guitar into a stompbox into headphones? Your pedal would always be engaged, but shouldn't it work? I figure if your voltage is the same, the lower impedance would mean more current, right (V=IR)? I've never tried it, but am wondering if it would work.

If you were to do something like what's listed above, what's the appropriate headphone impedance? My Sennheiser HD201 are 24 @ 1 kHz, which I think is pretty low for headphones.

What is the difference between the amp/mixer outs on something like a Digitech Bad Monkey? Does one have power amp/cab sim on something as simple as a $50 OD pedal?

Spudman
December 11th, 2009, 02:31 PM
You Do need a DI to run the bass direct through the snake. You'll also need a DI for an acoustic UNLESS it goes into some other preamp or amplification device first.

If you just get a good DI all your problems will be solved. Plug whatever you want into it and then it into the snake or console and you are ready to roll. Don't make it any more complex than it has to be. DIs are cheap and worth the investment.

Eric
December 11th, 2009, 02:36 PM
If you just get a good DI all your problems will be solved. Plug whatever you want into it and then it into the snake or console and you are ready to roll. Don't make it any more complex than it has to be. DIs are cheap and worth the investment.
I have a cheap DI that works allright, but I guess this was more a series of a theoretical questions. I'm trying to understand how voltage, current, impedance, and all of that junk fits together, and what runs at what levels.

markb
December 11th, 2009, 05:38 PM
It just takes whatever and outputs a low impedance signal suitable to feed a mic preamp. Low impedance signals are attenuated less by the capacitance of the cable hence you can send them down dozens of metres of snake without significant loss.
In a lot of cases it's just convenience as most acoustic pickups these days put out a low impedance line level signal via their preamps. Passive piezos are rare.

Ch0jin
December 12th, 2009, 04:25 PM
Eric, Does that answer your questions, or are you still after more in depth explanation of voltage/current/impedance interactions?

Eric
December 12th, 2009, 11:02 PM
Eric, Does that answer your questions, or are you still after more in depth explanation of voltage/current/impedance interactions?
The latter. I'd like a blow by blow response to my questions above -- I know some people on here have the knowledge, so it's just a matter of pulling it from them...

Ch0jin
December 13th, 2009, 07:33 PM
Well I'm an electronic engineer so I might be able to help with the theory, but I'm not really an audio expert and have zero DI experience, so FWIW I'll have a crack at it.

Woah update... Courier just arrived with my new A3 Photo printer and at the same time the mailman handed me a collection slip which means my new FX pedal (Boss RC-2) must be at the post office!!!!!!!!!

Umm.....

I'll get back to ya..You know, New toys and all ;)

/me runs from the room chanting "looper, looper, looper"

Eric
December 14th, 2009, 12:11 AM
...my new FX pedal (Boss RC-2) must be at the post office!!!!!!!!!

Umm.....

I'll get back to ya..You know, New toys and all ;)

/me runs from the room chanting "looper, looper, looper"
Those RC-2s look cool. Let me/us know how you like it.