M-Audio Mobile Pre -- calibration ?

[Anthony]

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]

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]

Anthony wrote:

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.

[brucek]

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]

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]

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]

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]

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]

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]

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]

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]

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.