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Need help understanding "D.I out", XLR out, etc.

Discussion in 'Amps and Cabs [BG]' started by Skel, Apr 15, 2006.


  1. Skel

    Skel

    Jun 19, 2005
    Boulder, Colorado
    I have always been confused by the term "D.I. out". If I'm not wrong, D.I. is an abbreviation for "direct input", and it seems like an oxymoron - direct input...out. I think I understand the XLR out, which is, I believe, the output signal taken after the preamp, with the option (sometimes) of having pre or post EQ. This is, I think, a 600 ohm (whatever that means) balanced output. I think "balanced" means there is some kind of noise cancelling signal, and if both ends are balanced, the noise gets cancelled by this signal that both ends understand. When an amp has both a D.I. out, and an XLR out, is the difference that one is balanced and the other is not, or is it simply the type of connector, as it seems a D.I. out is always a quarter inch connection and XLR is XLR. And why not call a D.I. out, just a D.O., or direct out? Would you use this connection to have something come "in" to the amplifier?

    Last, I am never sure when I use an XLR out, whether to use the pad or not - it seems like it doesn't matter. I am primarily interested only in running direct to a live mixing desk situation, but I'd like to understand all this stuff for live and/or recording.

    Sorry if my questions are confusing. I hope they are understood.
     
  2. dave_bass5

    dave_bass5

    May 28, 2004
    London, UK.
    Cant help with the rest but i always thought DI meant direct Injection
    Could be wrong though
     
  3. You are 100% correct, DI does indeed stand for Direct Injection.

    EDIT:

    It is called a DI because you are being put directly into a mixing desk, you are correct it is coming out of the amp but the signal is going into the desk.

    A DI is generally an XLR connection because (as mentioned above) it is the input on most sounds desks.


    On the back of my amp I have a DI output that is XLR and a jack that is a 'tuner' output but this can also be used a DI but this comes pre EQ where-as the DI (XLR connection) comes post EQ. I think the pre or post can be switchable as you say.

    Balanced as far as I am aware means it is a stereo signal but i'm not 100% on this.

    Hope that helps, I may not be explaining it very well, someone else may word it better than me.
     
  4. Balanced refers to the XLR style wiring which provides a third wire that helps shield the signal carrying wires and eliminate noise. Standard 1/4 inch connections don't do that.
     
  5. Skel

    Skel

    Jun 19, 2005
    Boulder, Colorado
    Oh Ok. So D.I. stands for direct injection - now this all makes sense. I guess this can be XLR or 1/4 inch, as I've seen both, but XLR is more common, I'm sure.
     
  6. paulraphael

    paulraphael

    Apr 13, 2006
    Brooklyn
    If you heard me play, you'd stop reading what I write.
    'Balanced' is a three-wire scheme for carrying a signal. It's used for microphones, instrument D.I. cables, and for some high end stereo interconnects. It was designed for studio use where there's a lot of electrical noise, and where long cable runs are often needed.

    A standard unbalanced signal uses two wires. One of them is live, carrying the changing a.c. voltage of the input device. The other is neutral, and carries the return current. In some cases the neutral wire is also the shield; in some the shielding is electrically isolated from the signal.

    In a balanced cable, both signal wires are live. Their polarity is reversed. In a situation where an unbalanced wire cable would have +4 volts on the live wire and the 0 volts on the neutral wire, the balanced cable will have +2 on one wire and -2 on the other. The third wire is the ground and is isolated from the signal.

    The point of this is that it elegantly eliminates noise. Any noise that the cable picks up (which it will because a cable is basically a big antena) will be picked up equally by both live wires. Because of the inverted polarity of the two wires, any signal that's added equally to both will simply cancel out to zero.
     
  7. dave_bass5

    dave_bass5

    May 28, 2004
    London, UK.
    One thing i can understand is on my SA450 i have a level control on the front of the amp that controls the DI level.
    I always though that XLR DI's worked at the same level (mic or instrument). also as a desk would have a gain control i cant see a use for one on the amp.
     
  8. Direct inject is where the signal within the mixer is brought out to a three pole jack socket where you have the option of breaking into the signal path to connect something else (like a compressor). Because you are inserting a new function in the signal path, this is known as 'direct injection'.

    A DI box usually takes your bass signal, and taps off some to send to a mixer. The rest goes to your back line (if you have one). It is not quite the same thing, but close enough to be given the same name.

    In summary, anything that splits off your signal to send to a mixer, may be labelled as a DI out, and is often a balanced feed through an XLR. Anything that breaks into your signal path may be labelled as a DI, and will usually be a three pole quarter inch jack (wired send, return, and ground)
     
  9. Triclops

    Triclops Guest

    Jan 14, 2006
    what difference in sound will it make if i send it "pre" or "post" gain?
     
  10. Skel

    Skel

    Jun 19, 2005
    Boulder, Colorado
    Tricops - I don't know the answer to your question, but I noticed you use an OLP Stingray. This is the 2nd time I've seen this mentioned in the last couple of days. What does "OLP" mean?

    Thanks - Skel
     
  11. Eddie95Z28

    Eddie95Z28 I play bass Supporting Member

    Apr 26, 2003
    Detroit Area, Michigan
    Pre would send the signal before it goes trough the EQ section and the effects loop. Post would send the signal after it goes through the EQ and effects loop. At least that is how it is on my GK amp and most other amps I've used.
     
  12. It may be helpful to think of "direct input" as a method by which to get your signal without the use of mics to a recording device or PA.
     
  13. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    No, I've always called this the Insert Point.

    The circuit the OP asked about is called Direct Inject because there is no mic. The signal goes direct from the instrument to the board.
     
  14. Jazzbassman23

    Jazzbassman23

    Apr 20, 2000
    Maryland
    Officially Licensed Product, I believe.
     
  15. I've just checked my Spirit manual - you are right, I have confused the Direct Out with the Insert Point.
     
  16. Brad Maestas

    Brad Maestas Gold Supporting Member

    Nov 26, 2003
    Oakland, CA
    To answer your question about ohms and the DI level control:
    A DI box often has a transformer that converts the low-level, high-impedance (~100K Ohms) signal of a bass guitar up to the +4dB standard low-impedance (600 ohms) recording level. A transformer is usually found in amps having an XLR out. Whenever there's a 1/4" out on an amp (like the tuner out) it's commonly line-level. (RCA connections for consumer-grade stereos are also line-level)
    The use of a balanced wiring scheme, high voltage level and low impedance makes the microphone cable a natural for carrying signals long distances without degradation. That is why it's so often used for DI outs on amps and why it's also important to understand how it all works.

    The different gain structures of various mixers, amplifiers and recorders have necessitated the need for a level control on the XLR out. I like to keep my bass' volume consistent so rather than turning my bass up or down to accomodate the engineer, I can use the DI level to control my send level independently of everything else. And even with the same equipment, engineers do things differently than others. One night, the engineer will say you're coming in too hot and ask you to turn the send down and on another night a different engineer says, "give me some more". You never know. That's why I have since changed my definition of DI to "Direct Interpretation". :D
     
  17. Skel

    Skel

    Jun 19, 2005
    Boulder, Colorado
    Yes, I too experience inconsistencies with engineers - some want more, some less and I just give them what they ask for. The thing that really boggles me is how a signal can have a known impedance, like ~100 K ohms. Impedance as I understand it, is simply resistance to alternating current (the signal). So, impedance relative to what? I understand how a signal can have frequency(s) and amplitude, but the impedance part is confusing. Beyond the scope of this thread for sure.

    Thanks - Skel
     
  18. dave_bass5

    dave_bass5

    May 28, 2004
    London, UK.
    Im still a bit confused about this level control on my SA450
    I have only seen a variable level control on a DI once, and thats on my SA450. i always thought that the DI goes in to the mixer at mic or instrument level and that the channel gain controlled the input level to the rest of the channel. also all the amps ive owned (even my ABM) have had no control over the DI level and that the DI is always pre master so you cant change the level apart from using the input level (and that would effect the amp sound as well)
     
  19. A primary reason for the "idea" of having a level control at the DI can be found in your post.

    The part where you say "I thought the DI goes into the mixer at mic or instrument level...."

    Well because there are so many variables (in addition to "line level") on any given mixer plus the myriad of ways cabling, patch bays, etc. can influence the issue you additionally must realize that it varies from brand to brand among mixers, consoles, PAs.

    So someone thought that having a level control on your DI is a convenience to you because its "normal" level may be too hot for any number of inputs on any number of mixers, recorders, PAs, foldback, etc.

    However, in practice you may discover that you need it wide open all the time with anything you connect it to. You may discover that you can't turn it up enough. Case-by-case basis.

    While I'm not familiar with the DI in your specific amp I will add that I usually prefer a separate, dedicated DI box like a Radial JDI. I say that because I've never met an itegrated DI that I liked mainly due to level weakness or hum. But I haven't tried all that many either.
     
  20. Vic

    Vic There's more music in the nuance than the notes. Supporting Member

    Oct 14, 2002
    Central Illinois
    Staff, Bass Gear Magazine
    FYI, it actually has three names that are all equally acceptable to the industry... "direct input, direct injection or direct interface", which, as already mentioned here, is referring to the mixing board's perspective.

    http://en.wikipedia.org/wiki/DI_unit
     

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