# M-Audio Mobile Pre -- calibration ?



## Anthony (Oct 5, 2006)

I searched the old threads but am still a wee bit confused on the final setup using an M-Audio MobilePre and a ECM8000 mic.

Wiring:
Obviously the mic goes to the sound card with an XLR cable. Now, how to go from the sound card to my system? Will I need to make some sort of mono 1/4" to RCA cable?

Also, how to run the calibration? Should I just use the XLR mic cable and go from in-to-out on the same channel? I seem to remember somebody getting weird feedback in the .cal file from that.

Thanks for the help.
A


----------



## brucek (Apr 11, 2006)

> Now, how to go from the sound card to my system? Will I need to make some sort of mono 1/4" to RCA cable?


The M-Audio has both a stereo 1/8" line out and also separate 1/4" left and right line-out. Easiest to use the 1/4" mono to RCA I would think. Plug the RCA into your receiver with a Y-cable to CD or AUX..



> Also, how to run the calibration


I don't know what people are using for the loopback on this device. Perhaps someone who owns this unit can comment.

brucek


----------



## boyce (May 9, 2006)

Anthony said:


> Also, how to run the calibration? Should I just use the XLR mic cable and go from in-to-out on the same channel? I seem to remember somebody getting weird feedback in the .cal file from that.


I don't have M-Audio Mobile, but I did try M-audio Firewire 400, I put cable from ch1 unbalance output to mic 1 XLR input, it work for room EQ, but it doesn't work for ETF /RPlusD, finally I change to M-audio transit, it work for both. :coocoo:


----------



## brucek (Apr 11, 2006)

> I put cable from ch1 unbalance output to mic 1 XLR input


A couple problems with this is that the mic amp provides very high gain (since a low output mic is usually feeding it), so the level may be hard to control. 
The other problem is that there is 48volts DC phantomed on the XLR jack to provide voltage for a microphone. I suppose the line output stage is capacitively coupled, but it doesn't seem like a good practice to me.

I admit I don't know how to produce a cal file for this soundcard.

Perhaps John M has used one of these.. Any suggestions?

brucek


----------



## Anthony (Oct 5, 2006)

I tried it two ways:

stereo 1/8" out to stereo mic in. Looked okay, but with some feedback at the top end.

Mono, 1/4" plug channel 2 out to in. Looked great. Mostly flat with a slight roll off on each end. That seemed to work best for me.

The XLR mic is fine with the phantom power. I upped the reference sound to 78dB and get -12dB on the input channel during level setting. Sweeps look good so far.

At 75dB and full gain on the input channel, I was getting just below -18dB and the error message, but so far things seem to work. When in doubt, trial and error 

Thanks for the input, guys.


----------



## boyce (May 9, 2006)

> A couple problems with this is that the mic amp provides very high gain (since a low output mic is usually feeding it), so the level may be hard to control.


adjust the on board gain control switch down.



> The other problem is that there is 48volts DC phantomed on the XLR jack to provide voltage for a microphone.


Turn off on board phantorn power switch.


----------



## basementjack (Sep 18, 2006)

I have a moble pre, and I used a 1/4 inch to 1/4 inch 1 foot patch cable I got from a music store - it was long enough to reach from front to back (it has 90degree connectors)

I have not used it with REW yet, but I'll try to in the next day or so. (I also have an M-Audio fastrack pro, which is what I played with last night)

- Jack


----------



## brucek (Apr 11, 2006)

> adjust the on board gain control switch down.
> 
> Turn off on board phantorn power switch.


Yep, good idea - smart. (I admit I don't know the soundcard in question very well)



> I have a moble pre, and I used a 1/4 inch to 1/4 inch 1 foot patch cable


Yeah, but then you are not creating a compensating calibration file for the signal path in use when you measure. You have bypassed the mic preamp which may well have a horrible response that you need corrected (that's the purpose of the cal file). The full loopback ensures that the cal file is providing an inverse correction to the output and input path used when measuring.

brucek


----------



## basementjack (Sep 18, 2006)

True Bruce, i wonderd if there wasn't a way to run the line out to mic in, but feared it would overpower it, Plus isn't the mic in balanced?


----------



## brucek (Apr 11, 2006)

> Plus isn't the mic in balanced?


Yep, but isn't there both a line-out balanced and unbalanced available..... just connect the balanced line-out to balanced mic in, and turn off the phantom power and adjust the gain until you are able to get a cal file....... that's my take anyway.

brucek


----------



## Anthony (Oct 5, 2006)

Next time I order from Parts Express, I'll get a stereo 1/4" phono and make an XLR to balanced phono cable (still have plenty of cable and XLR connectors) and compare the calibration files. Sadly that will be a couple of weeks, but I'll be sure to put that on the order.


----------



## basementjack (Sep 18, 2006)

The Mobile Pre USB does not have balanced outputs.

So it would seem that the best we can do to calibrate this device is to go unbalanced out to unbalanced in.


----------



## MustangMichael (Mar 30, 2014)

Greetings from the SW Colorado mountains. As intro, I'm perhaps a fairly advanced car guy but with little car audio experience. I've been learning what I can to update/modify/tune a car audio system I built over the winter and I've made some good progress. I believe there is more on the table. 

Hanatsu in DIYMA has been super helpful and suggested I try REW instead of TRTA so that's why I'm here. 

I've searched HTS and so far found 3 threads that mention M-Audio MobilePre USB (the earlier 1.1 model) and some reference to setup. 

Regarding my question: This thread came the closest so I'm bump-starting it again although it is a *very* old thread.

I've been using a Dayton Audio EMM-6 mic with this USB preamp with TrueRTA v4. The loopback I've been using for sound card calibration was an adapter cable from 1/8" stereo line out to 1/4" phono mono "Ch1 inst/line in". In TRTA, when testing the cal, I get a repeatable corrected nice flat line with that calibration and loop, but as people have aptly mentioned in this thread, that is with phantom power off and that path is NOT going through the XLR jack.

Furthermore, in REW, I continue to get an error message when trying to calibrate saying that more than 12db correction is necessary so it isn't a valid calibration. When saying ok and overriding that, making/saving the cal and testing - the test sweep is initially nice and flat but then shows a sharp roll upward from 1.5k to 20k. 

It doesn't appear to me that there was a clear consensus in this thread on best loopback connection. So with the above context, I hope someone can help with this question:

Has anyone used this USB preamp and found an accurate way to loop it and calibrate it for REW? 

Thank you,

Micke

edit: I tried using a 1/8" patch cable between the 1/8" stereo line out and 1/8" stereo mic in. It required turning the preamp's gain knob down very low, but I obtained what acts like a valid calibration with no error message. When testing that cal, it makes a very flat line.

I believe I'll try to find an adapter patch cable for 1/4" phono mono to XLR and see if I can get a similarly reliable cal there with very low gain. I have my doubts about whether that will work with phantom power on or not.. and is such a cable even available? Amazoning it now.


----------



## EarlK (Jan 1, 2010)

You'll see that you're trying to talk to ghosts // discovered by clicking on the previous posters names & then looking at the info available under those posters "User's Profile" .

Buy a 1/4"mono to XLR cable and calibrate the mic pre-amp ( of your choice ) .

That cable type is available from many sources .

Keep phantom power turned "off", during this procedure .

:sn:


----------



## MustangMichael (Mar 30, 2014)

EarlK said:


> You'll see that you're trying to talk to ghosts // discovered by clicking on the previous posters names & then looking at the info available under those posters "User's Profile" .
> 
> Buy a 1/4"mono to XLR cable and calibrate the mic pre-amp ( of your choice ) .
> 
> ...


Earl, thank you for your input. I appreciate it. I found mostly super long cables in that build but also found a mono 1/4 to XLR adapter so I can use one of my existing short XLR cables and plug it into one of the 1/4" jacks.

After such calibration, I'm assuming I would then need to use the same 1/4" jack (with adapter to 1/8") as the output to the car stereo head unit.. 

(FWIW: I read in feedback somewhere that monoprice sells such cables but that the pinout is not right on this cable type from that maker.)

With an ancient thread, I figured it was a shot in the dark. Thanks again,

mm


----------



## MustangMichael (Mar 30, 2014)

I doubt many people are still using M-Audio MobilePre USB v1.1 :rolleyesno:, but here is some info in case anyone else stumbles across this old thread as I did. 

I had some software problems so I had to use TRTA to test. With thanks to EarlK, looping the MobilePre (v1.1) with a 1/4 to XLR cable (1/4 mono line out to XLR with phantom power OFF) easily makes a good, totally repeatable flat hardware calibration.  If you've used this model of old preamp, you may already have seen that - depending upon other settings - XLR jack's mic gain control may have to be at or a bit under one quarter of control's scale or noise will prevent repeatable calibrations. 

To output for actual RTA work, I planned to use a 1/4 mono adapter to 1/8 stereo. So I thought to try to double check output method a couple of ways. First was: Using the same line out 1/4 jack with an adapter to 1/8 stereo and plugging into the stereo 1/8 mic input; still tests very flat with maybe a slight 1/4db bulge in the lower freqs and flat everywhere else. :sn: 

I tried 1/8 stereo line out to 1/8 stereo mic line in and found gradual 1.5db upward sweep from 80hz down. Probably not a big deal and may be close enough for people like me. Even so, it was much less deviation than when first testing without calibration. 

Anyway, for my uses, it appears I'll use the 1/4 line out to XLR in calibration with phantom power off. Then for RTA testing after the loop is removed, I'll use 1/4 mono jack out adapted to stereo 1/8 to the head unit's stereo 1/8 aux input. 

I can't prove if any of the above is accurate with phantom power ON. All testing was done with phantom power OFF. So that's as far as I can confirm it.

Thanks again, Earl. Looks like it's on for some more RTA work. 

mm

edit: I (finally) found my 1/4 to 1/4 cable and connected the same line out jack to the 1/4 line in next to the XLR jack. With the same quarter to XLR hardware calibration, the quarter quarter cable shows a perfectly flat curve just like the cal curve. FWIW, with this mic preamp, quarter/quarter cable may be close enough.


----------

