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Direct Injection Confusion


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I'm confused about Direct Injection. Would someone please clear this up for me? Is DI recording anything without sending the signal through a preamp first? I have a very modest US-428. I'm trying to figure out if the way I'v been recording is DI or not. Basically, there's four total inputs on the thing. Inputs A and B are balanced line level inputs for mics, and inputs C and D can be switched between line level and HI-Z. Obviously all inputs have A/D converters, but I don't believe they have any preamps. Would this be DI? :confused:
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DI simply means you're recording without microphones.

 

The first type of DI recording involves.. a DI. ;) DI's do not, typically, bring the instrument signal up to line level, though you can use some mic pre's as DI's and accomplish both impedance match/balanced line aspects of a DI with the gain increase of an input. DI's used to be used solely for electronic keyboards, bass, and some guitar work because a high impedance, unbalanced line will not run beyond 20' or so without a high risk of signal degradation and induction of RF noise through the cables. A DI solves these problems by lowering the impedance to that of a professional mic input and creating a differential balanced line which cancels noise similarly to how a humbucking pickup cancels noise, by combining positive (with signal) and negative (no signal) with reverse polarity. The signal passes but noise cancels itself out.

 

The more common use of the term direct injection these days seems to revolve around the plethora of amp modelers available to guitarists and bassists. Most of these units have high impedance inputs, just like an instrument amplifier, and output either a balanced or unbalanced line output, often as a simulated stereo field. With the advent of the Line6 Pod and its imitators, many musicians are happy simply dialing up a sound and running the output direct to the mixing console, rather than running through an amp. While this is certainly convenient, there are many sounds which are far from perfect in all modelers. You must decide if you're happy with the results of an amp modeler to decide if the convenience is worth the trade-off in dynamics and timbre.

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Direct injection is when there is a fuel injector for each individual cylinder instead of one or two injectors in a plenum/throttle body...

Oh wait, your'e talking about recording inputs...

See Neil's post.

 

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Lol, thanks Neil. So if you are using microphones, you must have a preamp before you run it into the mixer/recording interface, correct? If so, any mic level input will have a preamp before the ADC, if we're talking digital here. Whereas, if you are direct injecting, you don't necessarily need the preamp...
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Actually no - you will need a preamp of some kind. If you're going into your mixer via a channel you will be hitting the preamp.

 

To put it very simply, the DI is mainly used to match the impedance between sources that are not microphones and a mixer's channel input (preamp). There are other uses, but I think that's the main answer to your question. :wave:

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In simplest terms, a DI converts line and instrument level to mic level. The chain is instrument-DI-preamp. DI's typically have a balanced mic level XLR output, and an instrument/line level 1/4" TS input. They are desingend to be plugged into mic pres.

Hope this is helpful.

 

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I think your confusion is because the input section of a typical mixer has an xlr mic pre and a 1/4" line in. The 1/4" jack usually feeds a line level input, with gain adjustment.

 

It would be easier to understand if you were familiar with professional mixers, which use either separate, xlr jacks for mic or line input, or use a switch to reroute a single XLR to either mic pre or line level input.

 

The important idea is, with a DI, you are matching impedances, whereas when you use a Pod, impedances are matched in the processor and a line level output is typical.

 

In addition, some people refer to direct to tape as direct injection recording because they circumvent the mixer entirely on recording by using a separate mic pre. This greatly reduces the electronics between a mic and the recorder, but it's not a matter of impedance matching since most professional mics are already at 600 ohms or similarly low impedance.

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Thanks guys, but the clarity is still not all there quite yet. See, on my mixer, I have two xlr inputs plus two 1/4" inputs. They are routed to the same input, and they are both mic level. I am assuming this means they both have preamps. The other two inputs are 1/4" and can be switched between line level and HI-Z. Which inputs have preamps and which don't? The manual doesn't seem to really talk about preamps all that much.
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Originally posted by jmitch:

Thanks guys, but the clarity is still not all there quite yet. See, on my mixer, I have two xlr inputs plus two 1/4" inputs. They are routed to the same input, and they are both mic level. I am assuming this means they both have preamps. The other two inputs are 1/4" and can be switched between line level and HI-Z. Which inputs have preamps and which don't? The manual doesn't seem to really talk about preamps all that much.

I'll take a whack at it...

 

All of your inputs are pre-amplified somewhat, to send all inputs to the main outs.

 

Line level sources such as effects outputs, recorder/playback outputs, etc., can go into a Low-Z line-level input.

 

Microphones have extremely low output and have to be amplified (with what is called a preamp or mic amp) to be used with a low-z line-level input.

 

Bass guitar pickups, for example are high-z (high impedance) and will sound wrong (highs rolled off, etc.) when plugged into a mic amp or high-gain line-amp. A DI will change this impedance, either with a passive transformer or active circuitry, to low-z , and the sonic character of the bass will be true. You will typically plug the output of the DI into a mic amp.

 

As with all audio gear, there is a wide variety of quality and character in DIs. Your built-in high-z input functions as a DI, and may or may not sound the same or as good as a more expensive external DI.

 

As with all gear, plug your source into whatever input sounds the best. A great, transparent DI is probably the best way to get a clean Bass guitar recorded, or to send an electric guitar signal to a modeler.

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