whats the point of a DI box?

theshadow2001 · #1 03-18-2007, 02:10 PM

Whats the point of usinga DI box if your running straight into a desk only. No amp or anything else. Can't you plug straight into a desk and get the same results?

Or is it something to do with impedance or making a balanced signal. Do these things have much or an effect?

A9X · #2 03-18-2007, 03:04 PM

Depends on how close the desk is. If it's nearby on stage and the environment isn't too electrically noisy, going straight into the desk will be fine. If you need a long run, and/or have a noisy environment, the low impedance and balanced output of a DI will keep the noise down by at least a couple of orders of magnitude. For passive basses, long cable runs also mean lots of capacitance which loads the bass down and lowers the high frequency response and definition of the instrument.

PilbaraBass · #3 03-18-2007, 04:34 PM

A DI box converts the unbalanced signal from your bass to a balanced signal for the board.

Unbalanced is two wires, the ground acts as the return path for the signal.

Balanced is three wires, the two non-ground wires split the signal evenly. Therefore any noise that is picked up along the cable run is cancelled out.

Therefore a DI can be VITAL in eliminating noise.

For instance, I cannot run directly from my amp into our church's sound system...too much noise...

once I started going balanced DI , it's been as quiet as a church mouse (pun intended).

Baleen · #4 03-19-2007, 10:03 AM

Quote:

Originally Posted by PilbaraBass

Therefore a DI can be VITAL in eliminating noise.

Sorry to sound like a nudge, but I think it's better to say the DI won't introduce new noise, i.e. if the source/instrument is noisy, it'll still be noisy through a DI.

Cristo · #5 03-19-2007, 10:39 AM

Some DI's are equipped with additional features, such as EQ or amp "emulation.

These are designed to modify the signal such that it is more like the signal produced by an amp>cab>microphone signal chain.

OrangeSun · #6 03-19-2007, 10:52 AM

some amps have a balanced output. For example my Eden Wt800B has a "recording output" with its own level knob that is actually just a balanced output.

PilbaraBass · #7 03-19-2007, 04:19 PM

Quote:

Originally Posted by Baleen

Sorry to sound like a nudge, but I think it's better to say the DI won't introduce new noise, i.e. if the source/instrument is noisy, it'll still be noisy through a DI.

sorry, didn't mean it that way...of course it won't eliminate noises that are sourced at the instrument...

what it WILL eliminate is noises that are picked up along long cable runs...

on an unbalanced signal, the shield also is the return signal path...so noise picked up here cannot be cancelled

on a balanced signal, the two inner conductors operate at opposite polarity and then are amplified via a differential amp on the other end,

in this way, any common-mode noise (noise picked up "in phase" along the two opposite polarity conductors) is then cancelled out at the differential amplifier end.

of course, any noise that is picked up before this balanced signal (such as at the instrument, or on the instrument lead) is not cancelled out. Hence, your point.

PilbaraBass · #8 03-19-2007, 04:21 PM

Quote:

Originally Posted by OrangeSun

some amps have a balanced output. For example my Eden Wt800B has a "recording output" with its own level knob that is actually just a balanced output.

yep, that's a DI.

fokof · #9 03-19-2007, 06:07 PM

The outs on Eden amps are post eq, and they are noisy....

Baleen · #10 03-19-2007, 09:15 PM

PilbaraBass,
I think your explanations were great. I just wanted to help clarify the one point.

fokof,
yeah, I thought it was weird that the DI is post-EQ and not switchable, but I actually like it. My WT400 makes my 62RI Jazz (and others) sound just right when I use its DI and not one before the amp. I generally run the EQ almost flat anyway, so I'm getting pretty much just the color of the amp and not anything excessive. My Eden DI has always been clean and quiet - I run its volume half way up, and I hardly ever have to lift the ground.

I think some of the new Eden DIs are switchable - might be wrong though.

theshadow2001 · #11 03-22-2007, 01:59 PM

so if you have a low quality bass on a medium quality PA and your just your regular instrument cable's length away from the desk and your going into the desk without an amp. Chances are a DI box wont make much of a difference.

PilbaraBass · #12 03-22-2007, 04:27 PM

Quote:

Originally Posted by theshadow2001

so if you have a low quality bass on a medium quality PA and your just your regular instrument cable's length away from the desk and your going into the desk without an amp. Chances are a DI box wont make much of a difference.

yes, pretty much true...except, that impedence matching can be an issue...depending upon the board, the signal from the bass can be loaded down.

For the record, quality of bass doesn't really matter, since 99% of all passive basses work the same with regard to how the signal gets generated and leaves the bass.

theshadow2001 · #13 03-22-2007, 04:59 PM

Ok the impedance matching. I remember studying something like this in college but I can't quite remember what it was. I think the end of the lecture was that you want one impedance higher than the other. Does it stop signal loss if theres a large difference in impedance

A9X · #14 03-22-2007, 05:21 PM

Quote:

Originally Posted by theshadow2001

Ok the impedance matching. I remember studying something like this in college but I can't quite remember what it was. I think the end of the lecture was that you want one impedance higher than the other. Does it stop signal loss if theres a large difference in impedance

Low Z is less susceptible to picking up stray, unwanted signals of all sorts. A passive bass needs a high Z load or else it will be loaded down and this can change the character of the tone, for better or worse depending on your view.

So, an active DI should load the bass similarly to your amp (good for consistency), lower the output Z and make the signal balanced (good for rejection of stray signals) and some extra current drive to overcome the cable length and capacitance.

If your signal is noisy at the end of your usually 20' instrument cable, a good DI will simply transmit that to the desk.

PilbaraBass · #15 03-22-2007, 05:28 PM

Quote:

Originally Posted by theshadow2001

Ok the impedance matching. I remember studying something like this in college but I can't quite remember what it was. I think the end of the lecture was that you want one impedance higher than the other. Does it stop signal loss if theres a large difference in impedance

you remembered part of your lesson, but not the important part...you want the INPUT impedance higher than the OUTPUT impedance...

think of impedance as the opposite of "load".

Signal loss happens when the output impedance of a device (this case, the bass) is near the input impedance of the downstream device (this case, the PA)...

If the input impedance of the PA is high (ie load "low) then the effect of the PA drawing down the signal from the bass is minimalised, and the signal from the bass remains less affected.

The best way to determine your need, is to just plug your bass into the board...if you need to really crank the PA channel to get a decent signal level (i.e. volume), or your sound is a bit "washed out" or "tinny", then you should consider either a preamp or a DI, ...and if you're going to go preamp, you may as well get one WITH a DI...

I hope this helps...at least a little...

oh yeah, and the noise thing...A9X, "the TalkBass'er formally known as Dharmabass", is correct...hence the reason Low Z exists in the first place (noise rejection)

theshadow2001 · #16 03-22-2007, 05:41 PM

My friend keeps borrowing my DI box which I don't mind. I remember him sending me a text message saying his band would be screwed without it (slight issue getting it to him for a gig). This got me thinking that he probably wouldn't be screwed at all and so this thread was born.

He calls it the magic box. Doesn't know what it does how it works. What it's for. You just use it for pluggin bass into the desk. Crazy guitarists know nothing!