What about the influence of your preamp/mixer??

**JimP** · **09-13-09, 10:40 AM**

Last week, I got the SVS equalizer and was surprised as to the difference between what the predicted response with the equalizer sofware was compared to what I'm getting with REW.

This got me thinking about my REW setup. You know that we calibrate the sound card within REW. We also use calibration files for our microphones. But what about the preamp mixer?? how does that influence the test results? Unless I missed something, there is no way of knowing the influence of this device.

I use the Behringer XENYX 802 Mic Preamp. It has all kinds of adjustments for the manipulation of highs mids and lows. They're on reostats and we know how those can break down.

Is this really an area of concern?

I've been thinking about getting the Galaxy CM-140 microphone primarily to help eliminate the clutter. Now I'm thinking it might would have the added benefit of having a calibration file that take into consideration the preamp function.

**Wayne A. Pflughaupt** · **09-13-09, 10:54 AM**

Quote:

This got me thinking about my REW setup. You know that we calibrate the sound card within REW. We also use calibration files for our microphones. But what about the preamp mixer?? how does that influence the test results? Unless I missed something, there is no way of knowing the influence of this device.

The mixer can (and should be) calibrated with the soundcard if it’s connected to it.

Quote:

I use the Behringer XENYX 802 Mic Preamp. It has all kinds of adjustments for the manipulation of highs mids and lows. They're on reostats and we know how those can break down.

It shouldn’t be a problem, as all that would be compensated for with the calibration file. But it certainly wouldn’t hurt to streamline the signal chain. Personally I’d prefer a mixer where the aux send has a pre/post fader option. The former setting would bypass all tone controls and filters.

Quote:

I've been thinking about getting the Galaxy CM-140 microphone primarily to help eliminate the clutter. Now I'm thinking it might would have the added benefit of having a calibration file that take into consideration the preamp function.

Another option is a USB soundcard with a built-in mic pre-amp and phantom power. The Galaxy is a good option, as long as you keep in mind that for full range measurements, its larger mic element will be more directional than a mic like the ECM8000.

Regards,
Wayne

**JimP** · **09-13-09, 11:16 AM**

Hi Wayne..THANKS for responding.

Its been quite a while since I did my original sound card calibration. I could have sworn the mixer wasn't in the loop, but I may very well be wrong. I'll go back and try to retrace my steps.

As for sound cards with built in mic preamp and phantom power...can you make a recommendation. I'm currently using a Soundblaster live 24bit external USB. I'd prefer to stay USB as I'm using a laptop for this application.

**brucek** · **09-13-09, 07:02 PM**

Most of the soundcards with a mic input with phantom power are quite expensive.

A popular one is the M-Audio Mobile Pre.

brucek

**Anthony** · **09-14-09, 08:28 AM**

I have the Mobile Pre. It is not without it's idiosyncrasies, but once you get the hang of dialing in the gains and levels, it is a good sound card. The built in phantom power was the main reason I got it. I use it with the ECM8k and even built a jig to check speaker impedances and resistor values with it.

Their tech support is also very good. Whenever I have had an issue, they have responded very fast (and thoroughly).

Good luck.

**JimP** · **09-14-09, 08:51 AM**

I'd rather have one that just works without any need to contact tech support.

I'm leaning more toward that galaxy mic and keep using my soundblaster external usb sound card.

My current issue is finding that xlr to rca adapter so I can at least run a new sound card correction file that includes my preamp/mixer in the signal chain. Its very aggrevating to know that you have it somewhere and just can't find it.

**Anthony** · **09-14-09, 08:59 AM**

Well, the tech support calls I made were about specific gain values and input impedances. Stuff you won't find in the manual, but that I needed to know. Nothing was about the function of the unit.

**Wayne A. Pflughaupt** · **09-14-09, 09:22 AM**

So Anthony, as far as REW is concerned, was it pretty much "plug and play?" We've seen some of those sound cards have problems generating calibration files, etc.

Regards,
Wayne

**Anthony** · **09-14-09, 09:27 AM**

The only problem with the calibration file was that there is no easy way to loop the XLR balanced to the tip-sleeve input (unbalanced). You can use an adapter, but then it's not an apples-to-apples calibration, since the adapter will force the card to use the XLR in unbalanced mode.

This all being said, I just ran a 1/4" instrument cable from the tip-sleeve line out to the tip-sleeve line in and did the calibration that way. It is identical to the one I did by making an adapter cable.

The only weird part of this sound card is the adjustable gains for the inputs. It adds an extra complexity to setup balancing system volume, input levels, and then the line-in/mic gains. But once you get the hang of it, you can set it up for new measurements almost automatically.

**Wayne A. Pflughaupt** · **09-14-09, 10:43 AM**

Quote:

Anthony wrote:

This all being said, I just ran a 1/4" instrument cable from the tip-sleeve line out to the tip-sleeve line in and did the calibration that way. It is identical to the one I did by making an adapter cable.

So it has unbalanced ins and outs? That's good - brucek has documented that trying to include a mic preamp in the calibration file can be problematic.

Quote:

The only weird part of this sound card is the adjustable gains for the inputs. It adds an extra complexity to setup balancing system volume, input levels, and then the line-in/mic gains.

I assume that would be an issue with the Xenyx as well...

Regards,
Wayne

**Dennis H** · **09-14-09, 01:00 PM**

Quote:

The only weird part of this sound card is the adjustable gains for the inputs. It adds an extra complexity to setup balancing system volume, input levels, and then the line-in/mic gains. But once you get the hang of it, you can set it up for new measurements almost automatically.

That's one nice thing about the EMU 0202 and the newer Tracker. The inputs are unity gain with the pots all the way to the left so you can run it that way every time for a reproducible setup.

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