Q's about DI box's

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Pughbert

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This seems a real stupid question, but it seems to be one of those things that got left out for me. Basically, i know were and when to use DI boxes, (i think!) and make use of them regulary to send signal to my amp, then mic it, and send a DI signal straight to the desk, im also using them on bass, somtimes a.guitar too.
I know they impedance match - but why and what is this exactly? -
i know they'll take my line level to mic level - again - why?
And should i be using one on all line signals e.g keys?

Basically - im happy using one - but if i was asked what its doing exactly im unsure - if somone could help me here it would be great - cheers.

James
 
Those High Impedence unbalanced cords can't go far (10 feet or something like that) without the signal degrading.

The DI box as I understand it coverts that signal to a balanced low impedance signal that can go much longer without the signal degrading.

I noticed that with my keyboard that if I hooked up a DI box before the Preamp I got a much better sound than when I ran the Unbalanced connection directly to the line in on the preamp. It may just be me though.
 
I find it exactly the same, Bigwillz - and your description of what they do is pretty much dead on. :)
 
Yes, that was a pretty good description. As far as things sounding better because they go through a DI before a preamp, that is really a factor I think of the quality of the DI, the quality of the preamp, how far apart the preamp and the instrument are (i.e. cable length), and the desired sound. With cheaper preamps, a DI first might give a signal a little "help". In any case, the DI will change the sound a little. Depending on what DI are you using this may be good or bad.
 
Ok, to put into context ...

My Clavinova into my Soundcraft M12 sounds 'ok' ... 'fine'. It sounds better put through a Behringer DI100 first and then into the mic input. It sounds even better through a Behringer MIC2200 and THEN into the M12 line inputs ... yes, I know that's crazy. So why not just use the MIC2200 and skip the Soundcraft? Well, the Behringer simply doesn't have enough clean gain ... so it boosts and colours slightly before heading to the M12 to get a good enough signal for recording.

These are the kind of workarounds you have to devise when you're using cheap gear. Frustrating!!
 
noisedude said:
These are the kind of workarounds you have to devise when you're using cheap gear. Frustrating!!
Click to expand...
noise,

They seem frustrating now, but trust me, you are getting brilliant experience by working withing those "constraints" that you'll find invaluable as your experience matures even further. There's nothing like working on "limited" hardware (no dis intended) to hone one's skills.

Way back in The Dark Ages when we were cutting our programming teeth on the first Trash80 computers to come out, my buddies and I had to come up with ways of fitting the maximum amout of programming power into only 4K - or if we had a luxurious machine, 16K - of memory with no disc drives of any type to support us. To this day we value the skills we developed by working within those tight constraints, and still are able to throw tricks and techniques around that amaze co-workers who grew up in a world where anything less than 16 megabytes of memory was just silly to even consider. By being born with a silver RAM module in their mouths, they actually had a disadvantage in skillset learning.

So enjoy your "cheap gear" and your workarounds, noise. In due time you'll be working with the next U2 because of the custom skillset you're developing now on the "cheap gear". :D

G.
 
Soft samplers! The art is lost when you have 512mb of memory to play with instead of 2!!!!

I am pretty much at the point where I don't 'need' much more gear. And now, before I can justify monitor or mixer upgrades, I have to buy some serious instruments. As I get my room sorted, the sources will become the bottleneck all over again ....

It's a never-ending cycle!!!!

Nik
 
Pughbert said:
This seems a real stupid question, but it seems to be one of those things that got left out for me. Basically, i know were and when to use DI boxes, (i think!) and make use of them regulary to send signal to my amp, then mic it, and send a DI signal straight to the desk, im also using them on bass, somtimes a.guitar too.
I know they impedance match - but why and what is this exactly? -
i know they'll take my line level to mic level - again - why?
And should i be using one on all line signals e.g keys?

Basically - im happy using one - but if i was asked what its doing exactly im unsure - if somone could help me here it would be great - cheers.

James
Click to expand...

Impedance is the AC equivalent of resistance (DC).

If you have an amp and a speaker cabinet, the speakers act as resistors. 4, 8, 16 ohms are common. Sound familiar?

With mic and line level signals, the numbers are much higher, and you can get away with more of a mismatch, but it's important that low impedance signals feed higher impedance gear.

http://www.whirlwindusa.com/tech03.html

The artice above has all kinds of formulas and junk, but there are also some good descriptions.

I don't think that DI's do anything as far as changing levels.

The thing that direct boxes do very well is set up a properly balanced AC signal circuit. It has nothing to do with levels or impedance, but you basically have a twisted pair of conductors running through a cable with an outer shield. The shield is there to pick up surrounding noise from AC units, radio transmitters or whatever. Hopefully this keeps all this junk separate from the twisted pair. The shield is usually connected as a ground at all the equipment you're using, and this can be a problem if there's any noise signal there. A direct box will usually have a ground lift switch to break the sheild circuit, so if there's any buzz in the system, you can lift the ground at the DI and it will stop. Sometimes the equipment you're hooking up to won't connect the sheild anyway, so you can keep the circuit closed at the DI. A lot of times it doesn't make any difference, but the best setting is obviously the one with no buzzing.

The twisted pair inside the cable acts as a noise rejection system as well. If one of the signal wires picks up some noise, it's transferred to the other wire as well. 180 degrees out of phase. The 2 noise signals cancel each other out.

An unbalanced cable has one conductor in the middle, and an outer shield that acts as a shield, and also the second conductor. It will act like an antenna, especially if it's over 20 feet long. With a microphone, the signal is weak, so it will lose its strength over 20 feet. It's pretty common for a guitarist to plug a 20 foot cable into a stomp box, to another 20 foot cable, to the amp. It works, but it isn't always noise free, but a guitar puts out more signal than a mic. Basically, the shorter the better. If you're running unbalanced cables that are only 3 feet long, they should be pretty quiet. The longer you go, the more potential for noise.

AC works very well over long cable runs without signal loss, which is why electricity is not delivered as DC. Very few electric devices will actually use straight AC current, so there's usually a transformer or something involved to convert the AC to DC. The electric companies could deliver DC if they wanted to, but imagine having a power station every 20 feet down the road.

Balanced cables can handle very long cable runs.


sl
 
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