Why do we use DI boxes?

[eoinwalsh]

Hi. I don't know anything about the science behind electric bass sound and that's why I came here.

The first thing I want to know is exactly what a DI box is .

What is its function and why do we use it for live bass?

[echoSE7EN]

DI unit - Wikipedia, the free encyclopedia

[s_mcsleazy]

basicly its the best way for a soundman to get your signal without having to go through alot of stuff

[eoinwalsh]

Originally Posted by echoSE7EN

DI unit - Wikipedia, the free encyclopedia

That's great but I don't understand most of what's written there.

For example, 'The Direct Injection box takes a high impedance, unbalanced signal and converts it to a low impedance, balanced signal' means nothing to me. I don't know what this means.



Furthermore, why can't we just mic the bass amp like we do with guitar?


Thanks again.

[pedroims]

Originally Posted by eoinwalsh

That's great but I don't understand most of what's written there.

For example, 'The Direct Injection box takes a high impedance, unbalanced signal and converts it to a low impedance, balanced signal' means nothing to me. I don't know what this means.



Furthermore, why can't we just mic the bass amp like we do with guitar?


Thanks again.

you can do that too, but you will need a good mic, good amp and good cab so the soundman can get a good signal.

I prefere to use my cab and amp as monitor and send the signal to the mixer by using the DI.

[MrDOS]

In short, it sounds better.

Buying a mic that can get a full low-end sound is not cheap, at best. In addition, the sound of modern electric guitar has much more to do with the onstage amplification than does modern bass.

Does that help?

[bigfatbass]

I can answer some of that last part. Bass waves are much more difficult to capture with a mic because they require distance to stabilize and provide a strong fundamental note. You can close mic a bass cab and get a reasonable sound in the front of house, but you'll get a better, more stable, full-range signal from getting the bass off a direct line.


Ok geeks. I've been gentle. Have at him.

[nick_aua]

Well, as you have already read, the DI converts an unbalanced signal into a balanced one. What does this mean? Simply put, the balanced signal is protected by electromagnetic interference (our hated "noise"). Bring in mind all that stuff that lay on a stage: power lines, huge speaker magnets, other sound cables etc. All that stuff produce electromagnetic fields that would ruin your bass' signal (or any other audio signal) if it had to go through an unbalanced (unprotected) cable.

[uhdinator]

1. Balanced signals can go long distance to the mixer with no noise, instrument cables not good for over 20'

2. DI converts it to balanced XLR low impedance mic level which the mixer needs for it's input

3. The DI is before your amp so amp settings do not effect mixer levels.

4. It's a cleaner signal, no bleed from other things from a mic on a stage.

[WalterBush]

In addition to giving a mixer a balanced, low Z signal instead of an unbalanced, high Z signal, bassists use a DI for tonal reasons, as well.

Most bass cabs these days mix drivers, i.e. a 10 or 12" speaker with horns, a fifteen and 2 tens, whatever. A single mike at close range will NOT pick all of these speakers up, only the one that you place it in front of. That speaker will then act as a parabolic dish that focuses audience noise right into the mike; it happens with guitarists all the time, and is one reason some guitarists turn their amps away from the audience. Either way, you get more noise without accurately portraying what your bass sounds like. In addition, in order to get a hot enough signal to noise ratio that audience noise and stage bleed aren't an issue, you may end up turning up your amp to the point that it interferes with the mix out front; bass frequency management, especially on small stages, is hard enough without the bassist cranking their amp so that their miked cab comes through the mix louder than the guitarist's amp, or reflected audience noise, or the kick drum set up right next to the bass amp; you get the idea.

Also, the full range of bass guitar is pleasing to the ear; we don't necessarily need amps to tame the signal, so we can go direct. Plug a guitar in direct, especially with a distortion pedal, and the sound is awful. The full range of a guitar just doesn't sound pleasing on the human ear. Try it sometime, you'll see what I mean. We go direct because we can.

[eoinwalsh]

Originally Posted by WalterBush

Also, the full range of bass guitar is pleasing to the ear; we don't necessarily need amps to tame the signal, so we can go direct. Plug a guitar in direct, especially with a distortion pedal, and the sound is awful. The full range of a guitar just doesn't sound pleasing on the human ear. Try it sometime, you'll see what I mean. We go direct because we can.

Other than the above reason, are there any other reasons why we don't DI guitars?

I would have assumed that electric guitar would sound better after the DI box's conversion of an unbalanced, high Z signal into a balanced, low Z signal just like bass does.

Thanks for all the answers.

[pedroims]

Originally Posted by eoinwalsh

Other than the above reason, are there any other reasons why we don't DI guitars?

I would have assumed that electric guitar would sound better after the DI box's conversion of an unbalanced, high Z signal into a balanced, low Z signal just like bass does.

Thanks for all the answers.

Effects. You will usually see acoustic guitars using a DI though.

[PhiDeck]

Originally Posted by bigfatbass

I can answer some of that last part. Bass waves are much more difficult to capture with a mic because they require distance to stabilize and provide a strong fundamental note.

OP: Please ignore this and all other hogwash you may read to the effect that the wavelength of a low frequency acoustic wave has anything to do with sound detection or reproduction, except as pertains to the resonant frequencies of a room.

[Bassamatic]

re: "The Direct Injection box takes a high impedance, unbalanced signal and converts it to a low impedance, balanced signal' means nothing to me. I don't know what this means"

Musical instruments have not evolved along with the rest of technology. They are still made with a an old-fashioned high-impedance circuit, the way microphones used to be. Perhaps because the first mics and pickups were crystal and naturally high impedance or Hi-Z - 10K Ohms and up. They are very sensitive, but the electrical signal is very very small and easy to be interfered with by outside signals - AC power line hum and buzz, motor and light dimmer noise, RF from radio transmitters, etc.

As mic technology improved they developed circuits that were balanced having a plus and minus side, so outside interference gets canceled out. This is why mic connectors have 3 pins - +. - and ground. Mics also became low-Z (600 Ohms) and this also helps to eliminate outside interference. Cables could now be nearly any reasonable length without picking up hum and buzzes, etc.

The DI box splits your signal - one output passes through the DI to the amp unchanged, and the other output is converted it into a low-Z balanced mic signal to match the mic inputs on every recording and PA mixer.

It gives the engineer your sound completely unaffected by the acoustics of the room and by your amp and the mic that would be used to pick it up. It also prevents leakage from the nearby drums getting into the bass mic.

Sorry for the long-winded post - too much coffee this morning!

[Firesalt]

Originally Posted by eoinwalsh

Other than the above reason, are there any other reasons why we don't DI guitars?

No, that pretty much covers it without getting into the science of it... the distortion effect generally sounds like crap going thru a DI. It can be adjusted and address with amp modeling and filtering to make the soundwaves more pleasing on the end of the signal but it usually just easier to mic the guitarist's amp and not listen to him complain about why he has to change it because it sounds fine thru his amp...

[godofthunder59]

I bring my own mike and stand, no DI for me.

[mambo4]

Originally Posted by bigfatbass

Bass waves are much more difficult to capture with a mic because they require distance to stabilize a

As phideck mentions, this is utter myth. Bass signals will often be louder further from the speaker, but it's because 1.) high frequencies scatter more easily thus you hear "more bass" and 2.) room acoustics can reinforce certain low frequencies. No audio wave length takes any distance to "form completely".

[R. Laevinus]

Originally Posted by eoinwalsh

...are there any other reasons why we don't DI guitars?...

Because guitarists are whiny. That is all.

Really.

I'm serious.

Most bass players will be fine with the soundman using a DI on them. Even those that don't, generally don't mind if you (as soundman) take a DI along with the mike to blend at the board, or as a backup should the mike get knocked, the amp die, the amp settings change, etc etc etc. Very, very few bassists will not allow the soundman to use a DI feed.

However, guitarists get whiny when people tell them things in general, especially things that contradict what their favourite guitarist said. Things like: "Try to not overplay that riff, it sounds a little overdone," or "Can you try playing it this way, so I can hear what it might sound like," or "I'm not 100% sure you need three Triple Rectifiers and nine 4x12 cabs... this is a coffeehouse gig," or, my absolute favourite, "Why don't you try a DI this time?"

I DI guitarists whenever I can, especially those guys who use lots of effects. I've also persuaded several guitarists to try DI when they've paid me to record them, and they've all been very happy with the results.


I'm going to take a minute and go over the basic pros and cons of DI's and mikes, without going into the tech talk; this may help you to understand why some guys use DI's when they can and why some guys insist on mikes.

DI PROS
-Simple and fast to set up; not affected by placement or angle.
-All-passive circuitry (in most) means that very little, if anything, can go wrong; spilling a beer on one won't make any difference to it if it's well built. A DI can take a lot of abuse before it starts to go wrong, let alone give up.
-Clean, full-spectrum signal with accurate frequency response and negligible distortion.
-Not affected by room acoustics.
-Cannot pick up ambient noise, or bleed.
-Able to drive long cable runs without noise or high-end loss.
-Not susceptible to feedback.
-Universal: a good passive DI can be used on electric guitars, acoustic guitars, keyboards, basses, and really any source that outputs a high-impedance signal (basically any instrument that is designed for amplification/has a pickup).

DI CONS
-You can't hear the speakers 'breathe'. (I call BS: as I've said before, in other threads on the subject, I think the audience will hear the 'breath' of the line arrays just fine.)
-You don't hear the voice of the cab.
-They don't look cool.

DI MYTHS
-You don't get the tone of the amplifer. This is a myth, it is patently untrue. Any soundman worth his salt will place a DI between the head and cab if you request it.

MICROPHONE PROS
-They look cool.
-Putting one on a cab will make the guitarist stop whining, so you can focus on helping the singer with his hair.
-They pick up the sound of the cab.

MICROPHONE CONS
-Fragile. (Some mikes are very tough; be advised though that these tend to not have great frequency response, paired with high distortion levels.)
-Expensive. Even the cheapest usable mike is more than twice as expensive as the cheapest usable DI.
-Requires finicky placement in regards to the source, the audience, other noise sources, and the room. Sometimes this can be VERY finicky.
-Tying into the above point, can be rendered unusable if knocked out of alignment or off-axis. This can happen by somebody kicking the cable, too, not just the mike or stand.
-Picks up ambient noise and other noise sources (bleed).
-Can feed back.
-Not universal: a mike that is good for acoustic guitar is NOT good for anything else except woodwinds, drum overheads or orchestral strings; a mike that is good for electric guitar is NOT good for anything else except snare drum (and maybe vocals in a pinch); a mike that is good for bass is NOT good for anything else except maybe kick drum, and so on and so forth.
-Uneven frequency response.

MICROPHONE MYTHS
-A Shure SM57 sounds good on everything. It doesn't.
-A Shure SM58 sounds good on everything. It doesn't.
-You can just throw a mike in front of a guitar/bass cab and get a good sound. You can't.
-Even a cheap mike will sound 'better' than a DI. It really won't, unless the DI is garbage. (You can replace the word 'better' in this point with 'fuller', 'more vibrant', 'more alive', or anything along those lines.)
-Soundmen are too lazy to use them. Not really. Tossing a mike on a cab to shut a player up, is easy. Tweaking one to sound good and work well is hard and takes time. Most soundmen are perfectly willing to put in the time and effort, except and unless they're not able to (like when there's 10 bands sharing a stage in a night), or if the venue does not have the required equipment (mikes or stands or phantom powered channels), or if you just suck and aren't worth it.

[R. Laevinus]

Originally Posted by godofthunder59

I bring my own mike and stand, no DI for me.

See, that's the sort of thing I LOVE when I run sound. You're prepared, you're informed, you know what you want and how you want it and you shelled out the money to get it.

I'm willing to bet you set up your mike to get the tone you want, too. In cases like yours, I have no problems running mikes on cabs.

[eoinwalsh]

So does this mean that the signal picked up from a mic'd guitar amp is still unbalanced and high Z and thus much more prone to noise?


Thanks for all the great comments. Much appreciated.