M4 Input Levels: +4 dBu or -10 dBV?

[Dean Learner]

Not sure if this is the right place for this:

I have a dbx 266xl I want to add to to my input 'chain'. It has an Operating Level switch on the Output which toggles between -10 dBV and +4 dBu settings. From what I can gather on the interwebs, the main takeaway seems to be that a + 4 dBu output should go into a +4 dBu input, and the same with -10 dBV. I checked the user manual for my M4 but could only find references to ‘max’ input levels, ie:

XLR Max Level In: +10 dBu
TRS Max Level In: +16 dBu
Line In Max Level In: +18 dBu

I think all of this probably means I should set my 266 Operating Level to +4 dBu, but I really don’t know. Would +4 dBu would be the correct output level going into the M4, whether that’s XLR/TRS/Line In?

Related to that question, as I was looking through the manual I found this:
“Mic/line/instrument inputs with preamps
Connect a microphone, guitar or line-level analog input to the XLR/quarter-inch combo jacks with either a standard mic cable or a balanced cable with a quarter-inch plug.
☛ Do not connect a +4 (line level) XLR cable to the inputs (because of the preamps). Use a quarter-inch input instead.”

The above quote references a preamp, and I do have a Presonus Bluetube preamp that I could run a mic from, then into the dbx 266; would that mean that, if I’m routing a mic through that chain (and the Operating Level of the 266 was set at + 4 dBu) then I should use a ¼” TRS cable to go from the compressor to the M4 instead of an XLR?

Or am I overthinking all of this? I've got this chain l hooked up right now, using all XLR connections, and when I use it nothing blows up or sounds obviously horrible. But maybe there's a subtle effect on levels that I wouldn't notice until much later on, and I could make life easier during mixing by simply getting these connections correct.

[HCMarkus]

Not sure if this is the right place for this:

I have a dbx 266xl I want to add to to my input 'chain'. It has an Operating Level switch on the Output which toggles between -10 dBV and +4 dBu settings. From what I can gather on the interwebs, the main takeaway seems to be that a + 4 dBu output should go into a +4 dBu input, and the same with -10 dBV. I checked the user manual for my M4 but could only find references to ‘max’ input levels, ie:

XLR Max Level In: +10 dBu
TRS Max Level In: +16 dBu
Line In Max Level In: +18 dBu

I think all of this probably means I should set my 266 Operating Level to +4 dBu, but I really don’t know. Would +4 dBu would be the correct output level going into the M4, whether that’s XLR/TRS/Line In?

Related to that question, as I was looking through the manual I found this:
“Mic/line/instrument inputs with preamps
Connect a microphone, guitar or line-level analog input to the XLR/quarter-inch combo jacks with either a standard mic cable or a balanced cable with a quarter-inch plug.
☛ Do not connect a +4 (line level) XLR cable to the inputs (because of the preamps). Use a quarter-inch input instead.”

The above quote references a preamp, and I do have a Presonus Bluetube preamp that I could run a mic from, then into the dbx 266; would that mean that, if I’m routing a mic through that chain (and the Operating Level of the 266 was set at + 4 dBu) then I should use a ¼” TRS cable to go from the compressor to the M4 instead of an XLR?

Or am I overthinking all of this? I've got this chain l hooked up right now, using all XLR connections, and when I use it nothing blows up or sounds obviously horrible. But maybe there's a subtle effect on levels that I wouldn't notice until much later on, and I could make life easier during mixing by simply getting these connections correct.

Hi Dean... welcome to MOTUNation.

Set your 266xl to +4 and run it into your M4 using a TRS plug, not XLR. As MOTU recommends. This maintains good gain structure and reduces the risk of overdriving the M4 Input, which is the "Preamp" MOTU is referring to in its warning. Clarifying: The M4 XLR Inputs feed higher gain circuits than the TRS Inputs. The XLR portion of the input Combo Jacks (the "Mic Preamp") is intended to amplify microphone signals, which are lower level than the line-level signals the TRS portion of the Combo Jacks are meant to handle.

If you simply must use the M4 XLR inputs, consider running the DBX at -10. Better yet, get the right cable, TRS.

Have a good one!

[mikehalloran]

The M4 Line Inputs are +16. This was not listed in the manual and the support person I spoke with at the time had to get that from Engineering. +4 should be fine. Use TRS cables from a dBx 266xs.

I bought one of the first and was disappointed that my new Yamaha keyboard could not drive the Line Ins. They were advertised as being there for keyboards etc. Most keyboards do not output audio at line levels — for those, you need a step up transformer like Morley (Ebtech) Line Level Shifter or a DI box like the Radial J+4. Likewise, if you're not getting enough level from the dBx, either unit should be fine.

The only difference between the Morley and the discontinued Ebtech is that the Morley has XLR jacks in parallel with the TRS inputs. The transformer is the same (and it is excellent) and it doesn't matter which you plug into. It appears that Morley has retired their Ebtech brand but not the products.

https://www.sweetwater.com/store/detail ... el-shifter

https://www.sweetwater.com/store/detail ... el-shifter

[Dean Learner]

Thanks, all! So then I assume the TRS would use the line inputs on the back of the M4, ie. TRS = line, instead of the combo jacks?

No desire or need to use XLR. If anything, running a TRS to the line in is actually better since I don't have to run a cable around to the front of the M4.

Would the set up be the same if I have an instrument/unbalanced cable input into the compressor, or would I then need to run another instrument cable into the combo jack on the M4 instead?

[HCMarkus]

If the DBX is good with the instrument level TS input, you should be OK with the DBX plugged into the rear TRS.

Or you can plug instruments into the front jacks and use DAW plugins for compression if needed.

[Dean Learner]

If the DBX is good with the instrument level TS input, you should be OK with the DBX plugged into the rear TRS.

Or you can plug instruments into the front jacks and use DAW plugins for compression if needed.

The dbx manual says the 1/4" inputs accept balanced or unbalanced, so that should work. As you can tell, I have a pretty primitive set up so I'm figuring things out as I go.

Incidentally, the setup I have now 'works' by patching just with XLRs all the way through to the M4, but I'm guessing that probably causes some gain issues that might not be obvious but are there nonetheless. But it does work, and without any distortion or clipping or anything that sounds obviously terrible.

[mikehalloran]

The dbx manual says the 1/4" inputs accept balanced or unbalanced

Yes but the M4 is picky with unbalanced sources — the wrong cables cause distortion. Since the dBx does have balanced Ins/Outs, do use TRS cables.

[Dean Learner]

The dbx manual says the 1/4" inputs accept balanced or unbalanced

Yes but the M4 is picky with unbalanced sources — the wrong cables cause distortion. Since the dBx does have balanced Ins/Outs, do use TRS cables.

Ah, got it. Thanks!