Review of the M-Audio MobilePre

[Anthony]

First off, thanks to everyone here who helped me pick, setup, and get meaningful measurements using REW over the last year or so.

About 6 months ago, I decided I wanted to get smart on room treatments and super-fine tuning my BFD. I had done it by hand using a spreadsheet, RS SPL meter, and trial-n-error, and got pretty good results.

But as usual, education breeds unhappiness , so as I learned more about how good my room and system could sound I wanted better tools to know exactly where to apply the fixes.

Enter the M-Audio MobilePre. I went with this external soundcard because it supplies phantom power to the Behringer 8000 microphone, which is a monumental improvement over the RS SPL meter. I liked the idea of having the connections minimized: laptop to sound-card, sound-card to microphone. Additionally, I wanted a smaller form factor than the Behringer preamp board some people here use; which, while nice, is overkill for me since this is all I'll be using it for.

So, time for the review: the unit is heavy, but in a good way. Sturdy, clean lines, no extraneous controls, just the right number of connections. It's also powered off the USB bus, which is nice if you use a laptop. As far as inputs go, it has two channels and multiple options for those:
XLR mic in L/R
Balanced or unbalanced instrument/line in L/R
Stereo mic in

It can supply phantom power to the XLR jacks via a switch on the front. I believe the voltage is 48V, which is fine for the ECM8000.

For outputs, it has balanced/unbalanced 1/4" line jacks for each channel, a 1/8" stereo line out, and a 1/8" headphone line out with volume control.

Each input channel has its own level control on the front of the unit. All the 1/4" phono jacks auto-sense balanced or unbalanced mode, which makes connections much easier.

Installation is simple, but has a few bugs for XP. From an admin account, install the drivers without the unit attached, reboot, then plug it in. The main bug is that the admin account is the only one that can access the mixer panel for the unit. Other users can access the device, and even set the master volume through the advanced audio properties (right click on the tray speaker icon). I did not need this for any of my uses, but it could be annoying if you do. I will contact their tech support to see if there is a workaround to this.

Usage in REW is pretty simple. I tried to get a calibration file for it two ways. The first was stereo line out to stereo mic in. The cal file looked good except for the top octave, which seemed to get into some oscillating feedback. Plan B was to use an old guitar cable (unbalanced 1/4" phono) and link output channel 2 (R) to instrument/line in 2 (R). This cal file looked great, no feedback loop, and surprisingly flat. MUCH better than the laptop internal sound card (Sigmatel something or other).

After that, I hooked up the mic to channel 2. Remember to turn phantom power on if you need it for your mic. I was getting no signal and it took me a minute to figure it out. DOH! Once that was working, I set the levels. Unfortunately, 75dB SPL and the input gain at max only yielded -13dB on the VU meter, which I tried to pass by but REW gave me the "input signal too low" error. So I upped the measurement to 78dB, turned the gain down just a bit (still almost at max), and got around -9 to -10 dB on the VU meter. After that, all measurements went smoothly. I only needed to readjust when I enabled filters (which made the overall output a bit quieter). Even then, it was adjusting the gain on the receiver, not the sound card.

My room and sub results are subjects for another thread, but suffice to say they looked good. Almost exaclty what I was expecting, except for the extreme low end, which the RS SPL meter doesn't seem to capture as well. I got a lot more detail, although it was already in the roll-off region so there was little I could do to correct it.

One thing to note was that I only needed 4 filters to get a decent correction applied with this setup. My old laptop SC + RS SPL meter measurements needed 8 filters to get fixed. I'm wondering if some of the corrctions I was applying with the BFD were tuning errors in the RS SPL meter and not actual room problems.

Overall, I give the M-Audio MobilePre an A for performance, B+ for ergonomics, C for software (it would be an A if they fix the multi-user problem), and a B for value (it is a tad expensive -- but worth it).

Anth

[basementjack]

Cool review - I'm going to have to go home and log in as adminsitrator - the level thing bugged me - it's especially bad if it gets set too low and you can't change it.

For what it's worth, I have both the moblepre USB and the fastrack Pro, and the fastrack pro was also returning pretty low levels, with the input volume turned to max, it barely registered.

- Jack

[super josh]

Hi Guys, this is my first post on the Forum and I must say there appear to be some very knowledgeable and enthusiastic people on here
I received my MobilePre yesterday. I decided to buy this model as it is powered solely by the laptops USB and also provides the phantom power to run the ECM8000. This will be useful for me when I tune up mine and my friends car audio installations. I also assumed that the sound quality would be better than an internal laptop sound card as this unit is aimed at the Home Recording studio market.
Like the OP I thought the unit looked fairly well made and so proceeded to install the drivers.
This is where my problems started. I am running XP SP2 and installed the drivers from the CD, at the end of installation the Software didn't ask for the MobilePre to be connected to the USB port. I connected it anyway and the usual PnP started to execute, but it never completed.
So I rebooted the machine and managed to PnP the MobilePre, but then the MobilePre control Panel, when maximised from the system tray would say that it couldn't detect a unit and to re-install the driver (I am running from an Admin account, as this is the only account on the machine) although the MobilePre would show up correctly in the windows 'Sound and Audio Devices' applet.
So I looked on the M-Audio website knowledge base and for updated drivers too. I had installed the shipping driver 5.10.00.3516 and the only way that I could get the M-Audio control panel to work was by rolling back the driver to version 1.0.0.12, which I downloaded from their website.
So far I am not that impressed with the card, it's not like this is a generic reference design out of China. Someone like M-Audio should be able to write a decent WDM driver

So then onto calibrating it using REW. I connected the 1/4" TRS from the output of Channel 2 to the 1/4" TRS on the input of channel 2. Adjusted the gains so that I had around -8dB on both the input and output VUs. Ran the cal. and the graph looked okay, with a slight hump at the top end, BUT the response at the bottom end was just like the graph in the help section of the cheap internal sound card with the responds dropping off sharply at around 20Hz. I would have expected a flatter frequency response or am I expecting too much from this card? Or have I done something wrong?

Sorry for such a long and whinging first post.


Josh

[brucek]

What was the scaling on the graph when you looked at the soundcard cal?

What were the input and output connections you used (refer to the pic attached).

Since the XLR mic input will be used when you measure with REW, don't you think it should be included in the loopback path for the soundcard calibration (with the phantom volts off of course). We want to loop the exact input/output jacks used, so the calibration file can provide the inverse compensation. Might be tricky with the large gain the mic preamp provides...

I wonder what loopback connections were used by other members here with this soundcard...



brucek

[super josh]

Hi Bruce,
Thanks very much for the quick reply
I connected the 1/4" ch2 'unbalanced output' on the rear panel of the unit to the ch2 '1/4" balanced inst/line input', which I was led to believe would auto sense and switch to unbalanced, if necessary. This seems to be the way that both Anthony and basement jack configured theirs.
I understand what you are saying about having the whole mic path wired in for the calibration. But according to this post the MobilePre doesn't have balanced outputs. So calibrating unbalanced to unbalanced is the best we can do.
As for the graph scaling, I will have to reconnect everything and run through it again, as I didn't save a copy of those details. I will post up my findings later on.

Once again, thanks for the quick response and help so far



Josh

[brucek]

As for the graph scaling, I will have to reconnect everything and run through it again,

But you saved the soundcard.cal file? Start REW and the soundcard file will load every time and be shown on the screen. Set the scale to 45dB to 105dB and 10Hz to 20KHz. How does it look? Maybe post it so we can see.

Here's my soundcard.cal with two different scale. One looks good and the other doesn't... I just thought you may have had your scale so narrow that it looked poor.

Soundcard.cal normal scale




Soundcard.cal exaggerated scale.



brucek

[super josh]

Hi Bruce,
Here is my cal plot. Do you think it falls off rather sharply in the 40 - 20Hz region?







Josh

[basementjack]

Wow guys, I keep meaning to get back to this (I've got both the moble pre usb and the fastrack pro)

Too much Xbox 360 and HD-DVD!

I guess thats a good thing - my audio can't be THAT bad if I'm not so bothered by it to put down the controller for an evening!

;-)

[brucek]

Here is my cal plot. Do you think it falls off rather sharply in the 40 - 20Hz region?

It doesn't look too bad to me. Either way, if that's the response, then it will inversely compensate to result in a flat response.

Did you do a response with the loopback still in place and get a perfectly flat line?

brucek

[super josh]

brucek wrote:

Did you do a response with the loopback still in place and get a perfectly flat line?

Hi Bruce,
I supppose that's the acid test? I just ran a response with the loopback in place and flat as a board
So everything looks good then. Thanks very much for your help. Just need to test it on a 'live system' now.



Josh