X32: DI Box OUT to Mic In or AUX In?

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X32: DI Box OUT to Mic In or AUX In?

Post by OliverATX »

Hello!

I hope everyone is doing great!

Here is yet another question for the smart folks on the board.

I am having a hard time understanding why I would run the output of my DI channels into a regular (Mic Pre) channel on the X32, rather than into an AUX In. I have 4 channels coming out of my DI box, a direct Bass signal, direct Guitar signal, Roland SPD-ONE and a synth (I am also mic'ing the Guitar cab and bass cab, but that is besides the point).

The question is why I would go from the balanced XLR OUT from the DI box to a standard input XLR (Mic Pre) channel on the X32? Why would I not rather go into one of the 6 (balanced) TRS AUX inputs? If I come out of the DI box, I would not utilize the Mic Pres anyways, correct? So, why waste them?

Maybe I am misunderstanding something, so any help is greatly appreciated!

Best,

Oliver
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by Funkyflash5 »

DI's convert instrument signals to mic level, so you want a mic pre to follow. If your source is already line level and you don't need to balance it, and don't want to use up a mic channel, then an aux in would be fine.
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by Mike Stranks »

Funkyflash5 wrote: Wed May 18, 2022 4:59 am DI's convert instrument signals to mic level, so you want a mic pre to follow. If your source is already line level and you don't need to balance it, and don't want to use up a mic channel, then an aux in would be fine.

Precisely! :thumbup:

... and to be crystal-clear (following uncertainty in another thread) Line/Aux Ins are not interchangeable with Inst (Instrument) Ins. Inst ins are designed for the direct connection of electric guitars that have different electronic characteristics to 'normal' line/aux sources.

DIs always connect to mic ins.
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by Hugh Robjohns »

OliverATX wrote: Wed May 18, 2022 1:48 amThe question is why I would go from the balanced XLR OUT from the DI box to a standard input XLR (Mic Pre) channel on the X32?

The very simple answer is that all DI boxes take in an unbalanced instrument (or line) level signal, and convert it (which includes attenuating it) to create a balanced mic level signal which can then be routed from the stage to the mixing console with all the other on-stage mic signals.

So a DI box output must always connect to a mic preamp. Moreover, most active DI boxes need phantom power from a mic preamp to work!

Why would I not rather go into one of the 6 (balanced) TRS AUX inputs? If I come out of the DI box, I would not utilize the Mic Pres anyways, correct? So, why waste them?

There is a school of thought that argues attenuating a line level source through a DI box and then boosting it again in a mic preamp is wasteful and potentially damages the signal by adding unwanted noise and distortion.

In practice, though, noise and distortion is vanishingly small in modern preamps and thus usually completely irrelevant, whereas the practical convenience and safety value of using a DI box remain significant.

However, if you don't have any mic preamps available and need to use a line input on the desk instead you have two options.

1. Connect the unbalanced (or balanced) line source directly to the console line input. This often works fine, but with unbalanced sources in particular there is a greater risk of unwanted interference and ground-loop hums and buzzes.

Also, if the source suffers an electrical fault there is a grave risk of damaging the console too (and vice versa).

2. Connect the unbalanced (or balanced) line level source to the console line input via a line isolation box, such as the ART DTI (other brands are available). I use this arrangement a lot myself.

The transformer in the line isolation box provides a balanced output, which helps to prevent interference on long cable runs, and also provides galvanic isolation (like a DI box) which prevents ground-loops and also guards against an electrical fault on one side damaging the equipment on the other.

As the transformer doesn't alter the signal level there is no requirement for a mic preamp -- a line level source can feed a line level input.

Bear in mind, though, that while this arrangement will usually work fine with electronic sources like keyboards, drum machines, dj consoles, iPads, and so on, their output signal level is often 10-20dB lower than standard line level so you will typically need to dial in some extra gain through the line input Trim control (or whatever is available in the console).

Also, the input impedance (either directly or via the line isolation box) is normally too low to work satisfactorily with electric guitars or basses. (DI boxes are designed to present a much higher input impedance specifically to keep guitars and basses happy!).

Hope that helps with the confusion and mystery, Oliver.
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by OliverATX »

Wow, thank you all for the detailed replies (especially @ Hugh Robjohns).

I have a few follow-up questions if y'all don't mind (more specific to my personal situation)

One thing up front. I would like to pipe all TSR 1/4 through the DI rack to avoid having to run cables through the back of the rack- stupid reason, but I guess I am OCD that way :shifty: So, if it does not create any issues, I would like to do that, even if not necessary. If it creates issues, then obviously not.

To get a bit into the nitty gritty of my situation I did some research on the hardware that I am using.

First, some approximate, ballpark baselines for levels that we hopefully can all agree on (please anyone correct if substantially incorrect):

-MIC-LEVEL ~(-60 and -40 dBu)
-INSTRUMENT-LEVEL ~(-20 dBu)
-LINE-LEVEL ~(+4 dBu)
-DI BOX OUTPUT-LEVEL ~(-15-25 dBu)

The X32 mixer non-clip maximum input levels from the spec sheet:
-XLR (Balanced) +23 dBu
-TRS (Balanced) +16 dBu

The X32 mixer input impedance from the spec sheet:
-XLR (Balanced) 10 Kiloohm
-TRS (Balanced) 40 Kiloohm

The DI800 direct box maximum input levels:
+18 dBu, +48 dBu (-30dBu PAD engaged)

The DI800 direct box maximum output levels:
+23 dBu (balanced)
+16 dBu (unbalanced)

The DI800 input/output impedance from the spec sheet:
1 Megaohm/ 680 Ohm

So, my incoming connections are as follows:

1) Direct out from bass amp line-out (line-level balanced)- assuming ~+4 dBu
2) Guitar out (instrument-level unbalanced)- assuming ~-20 dBu
3) Keyboard line-out (line-level unbalanced)- assuming ~+2-4 dBu
4) Roland SPD-ONE (should be line-level, but known to be weak unbalanced)- assuming ~-5dBu to -10dBu

I am not trying to be beat a dead horse here and I understand that the DI box is designed to bring up unbalanced signals to balanced mic level signals or help bridge large distances. However on the X32 the acceptable input levels for both XLR and TRS(AUX) seem to be in a similar range. All signals I would put through the DI800 (no matter if balanced or not) would exit as balanced signals, which both the XLR and TRS ports can accept. Also, I can adjust the output level on the DI800 to meet the signal requirements.

I guess I am still wondering why not to use the TRS AUX ports after running through the DI800 or if it would hurt the signal path in some major way?

Thanks for your patience with this.

Oliver
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by AlecSp »

While the same questions keep being asked again and again, the real tragedy about threads like this is they show the lack of initiative just to try things out and learn from experience.

It's all very well to learn the theory of how DIs work, but why not just try plugging the output of your DI into the line input and see what happens. If it's an active DI, then nothing will happen as it won't be getting phantom power. Otherwise, see how low the level is. If it's workable, sounds OK and is and not more noisy than using the mic input, then why not use it.

It's the same way that trial and error showed that many desks with limited mic inputs could get away with mics (often tom mics that were loud signals anyway) going in to line inputs. My 01v96 expanded from 12 inputs to 16 that way.

We're so used to everyone having all the toys to do things right that no-one ever just plays with stuff to see what works, what doesn't, and what has an interesting effect. So much of our classic music was done the "wrong" way, with great results.

And, back to your question about running line inputs through the rack DI. OK, do it that way if it pleases you. You're making life more difficult for yourself, and it may sound slightly more noisy (though it might subjectively be pleasing), but in the end it's a potato/potoarto thing.
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by OliverATX »

@AlecSP

I am all for learning and trial-and-error. I will spend countless hours trying to figure something out. However I do not think that this precludes me from asking questions 1st, trying to avoid others mistakes and potentially damaging my equipment.

I also believe that it is best to go with a solid foundation of foundation of knowledge into a trial-and-error process rather than trying to figure everything out from bare metal. In addition as you mentioned yourself there are certain areas where something may sound good but is objectively the wrong thing to do resulting in sub-par results. I do prefer the methodology of asking questions 1st before I regret my decisions.

Best,

Oliver
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by Sam Spoons »

By the same token, try not to overthink things, for example the XLR inputs on an X32 are capable of taking a line level input but a better way of getting instrument/line level signals into them is by using a DI box as was explained above.
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by OliverATX »

Sam Spoons wrote: Wed May 18, 2022 9:02 pm By the same token, try not to overthink things, for example the XLR inputs on an X32 are capable of taking a line level input but a better way of getting instrument/line level signals into them is by using a DI box as was explained above.

Yes, trying to not overthink it. However my take away from the previous post was that a DI Box always has to be connected to a mic input, not a line input. I think that was pretty much mentioned verbatim.
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by Mike Stranks »

AlecSp wrote: Wed May 18, 2022 8:38 pm While the same questions keep being asked again and again, the real tragedy about threads like this is they show the lack of initiative just to try things out and learn from experience.

It's all very well to learn the theory of how DIs work, but why not just try plugging the output of your DI into the line input and see what happens. If it's an active DI, then nothing will happen as it won't be getting phantom power. Otherwise, see how low the level is. If it's workable, sounds OK and is and not more noisy than using the mic input, then why not use it.

It's the same way that trial and error showed that many desks with limited mic inputs could get away with mics (often tom mics that were loud signals anyway) going in to line inputs. My 01v96 expanded from 12 inputs to 16 that way.

We're so used to everyone having all the toys to do things right that no-one ever just plays with stuff to see what works, what doesn't, and what has an interesting effect. So much of our classic music was done the "wrong" way, with great results.

And, back to your question about running line inputs through the rack DI. OK, do it that way if it pleases you. You're making life more difficult for yourself, and it may sound slightly more noisy (though it might subjectively be pleasing), but in the end it's a potato/potoarto thing.

This is not intended as an arsey response; merely expressing a counter point of view...

As we gain in experience most of us try fudges from time to time to see if we can get away with it. Needs must and all that..

But a significant percentage of the queries here are from people who are just starting out in their discovery of the world of audio, recording and live-sound. My view is that it's much better to explain what a piece of equipment is designed to do - and what it's not designed to do - so that they gain a good grasp of core principles. Encouraging a 'try it and see' approach when people don't understand the fundamentals could result in needlessly poor performance, the magic blue smoke - or much worse.

You may think I've misrepresented your position and you were more nuanced. I've learnt the hard way that nuance doesn't always seem to work well in forums... :)
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by Hugh Robjohns »

OliverATX wrote: Wed May 18, 2022 7:13 pmFirst, some approximate, ballpark baselines for levels that we hopefully can all agree on (please anyone correct if substantially incorrect):

-MIC-LEVEL ~(-60 and -40 dBu)
-INSTRUMENT-LEVEL ~(-20 dBu)
-LINE-LEVEL ~(+4 dBu)
-DI BOX OUTPUT-LEVEL ~(-15-25 dBu)

This is all grey area stuff, and very much 'nominal' rather than real world... so don't get too bogged down in specific numbers. There are working ranges around the nominal levels.

The X32 mixer non-clip maximum input levels from the spec sheet:
-XLR (Balanced) +23 dBu
-TRS (Balanced) +16 dBu

What's actually of more importance than maz levels in your application is what gain is available to the line (aux) and mic inputs. What is the lowest signal level they can raise to nominal line level?

The DI800 direct box maximum input levels:
+18 dBu, +48 dBu (-30dBu PAD engaged)

The DI800 direct box maximum output levels:
+23 dBu (balanced)
+16 dBu (unbalanced)

The implication from these numbers is that the dI box is attenuating the signal by around 25dB, which sounds plausible... and so you'll need at least 25 dB of gain available via whichever input path you use.... although I note 20dB of that could come from the di800's own +20dB boost facility.

I guess I am still wondering why not to use the TRS AUX ports after running through the DI800 or if it would hurt the signal path in some major way?

Nothing to prevent you trying it!

The fact is that your DI box situation is highly unusual because:

1. Your DI box is mains powered and doesn't rely on phantom power to work, so you don't need to connect to a preamp to power the box.

2. Your DI box has a 20db gain mode which goes some way to overcoming the normal format incompatibility of feeding mic level to a line input.

The potential downside of your intention is ending up with more noise added to the source than you'd like, but until you try it you won't know.

Nothing will blow up or be damaged if you connect as you outlined in your post.
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Re: X32: DI Box OUT to Mic In or AUX In?

Post by OliverATX »

Hugh Robjohns wrote: Wed May 18, 2022 10:43 pm
This is all grey area stuff, and very much 'nominal' rather than real world... so don't get too bogged down in specific numbers. There are working ranges around the nominal levels.

Yes, I figured as much, thank you!

What's actually of more importance than maz levels in your application is what gain is available to the line (aux) and mic inputs. What is the lowest signal level they can raise to nominal line level?

OK, that makes sense. I guess if I run it through the DI, it becomes less of an issue, but appreciate the insight!

The implication from these numbers is that the dI box is attenuating the signal by around 25dB, which sounds plausible... and so you'll need at least 25 dB of gain available via whichever input path you use.... although I note 20dB of that could come from the di800's own +20dB boost facility.

Makes sense.

I guess I am still wondering why not to use the TRS AUX ports after running through the DI800 or if it would hurt the signal path in some major way?

Nothing to prevent you trying it!

The fact is that your DI box situation is highly unusual because:

1. Your DI box is mains powered and doesn't rely on phantom power to work, so you don't need to connect to a preamp to power the box.

2. Your DI box has a 20db gain mode which goes some way to overcoming the normal format incompatibility of feeding mic level to a line input.

The potential downside of your intention is ending up with more noise added to the source than you'd like, but until you try it you won't know.

Nothing will blow up or be damaged if you connect as you outlined in your post.

Thank you again for the time and effort you put in to answer my questions! Maybe someone can benefit from this in the future when perusing the board for similar questions/answers.

I definitely feel confident now to start pluggin away without feeling I am going to release some magic smoke :lol:
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