# What about the influence of your preamp/mixer??



## JimP (May 18, 2006)

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.


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## Wayne A. Pflughaupt (Apr 13, 2006)

> 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.



> 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.



> 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


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## JimP (May 18, 2006)

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.


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## brucek (Apr 11, 2006)

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

A popular one is the M-Audio Mobile Pre.

brucek


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## Anthony (Oct 5, 2006)

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.


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## JimP (May 18, 2006)

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.


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## Anthony (Oct 5, 2006)

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.


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## Wayne A. Pflughaupt (Apr 13, 2006)

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


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## Anthony (Oct 5, 2006)

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.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Anthony said:


> 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.



> 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


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## Dennis H (Apr 2, 2007)

> 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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## rsritchey (Jan 27, 2010)

I have the E-MU Tracker Pre, and I can't seem to get enough gain with the Dayton Audio EMM-6 while setting the input gain at full counter clockwise. Since there is no way to adjust gain in the software, is there any other way to properly calibrate my setup?


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## Wayne A. Pflughaupt (Apr 13, 2006)

You didn't give us much to go on. Why do you think you're not getting enough gain? BTW, do you have the Tracker's phantom power switched on?

Regards,
Wayne


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## rsritchey (Jan 27, 2010)

Thanks for the quick reply Wayne.

Phantom is on, and I can get a measurement by setting the input volume on the Tracker Pre to approx. 12 oclock. 

Here is the procedure I followed:

_Here's a "quick step-through" brucek wrote up some time back.

1. Prepare to run the Check Levels routine (Settings icon, Soundcard tab) selecting Check/Set Levels with Subwoofer in the Levels pull down box, with the SPL meter at the listening position and the dial of the meter at 80dB position. 

Change Input Device Input and Output Device Output from Default to USB Audio, or the name of the soundcard, if that option is available, and Speaker for output, and Line In for input. 

Begin the Check Levels routine. Ensure the REW output VU meter is at -12db and the Sweep Level at -12dB. If those fields are blank, check the two Control Mixer Volume boxes.

Set the Wave Volume at 1.000 and the Output Volume about ~0.500. (If those fields are blank,). 

Adjust your receivers volume control so the actual standalone Radio Shack SPL meter reads ~75db at the listening position.

*Then adjust REW Input Volume to end up with -18dB on the REW input VU meter.*

2. Still in the Settings section, run the Calibrate SPL routine (in the Meter Tab) to match REW's SPL meter to the real SPL meter to ~75dBSPL. Make sure the “C Weighted SPL meter is checked.

3. Close Settings window. Run the Set Target Level routine (Target Settings icon to left of screen), which will set the target to ~75dB. Also, set the Cutoff, which is the crossover frequency you’re using

4. Run the Measure routine and set the End Frequency to 200Hz for subwoofers._

My problem is during the "Check Levels" procedure I think. I set the volume of my AVM-30 to get a reading of 75dB on my Radio Shack meter and then look for -18dB at the right input. Without adjusting the knob on the Tracker Pre, the input level is too low. If I try to do a measurement, a warning box appears. 

Based on posts by Dennis H and others, I assumed I should be able to use the Tracker Pre with inputs set to Unity (full counter clockwise). This may not be the case, but for consistency I would like to be able to leave the input knob in a known state.


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## Wayne A. Pflughaupt (Apr 13, 2006)

If you're not getting enough signal from the pre amp, all you need to do is turn the gain control on the mic input clockwise to increase the output to the program. The Calibrate Soundcard routine also has a level input adjustment.

Regards,
Wayne


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## rsritchey (Jan 27, 2010)

During the soundcard calibration procedure, I used a 1/4 inch phone plug loopback cable and noted that the input was -12.3dB when the output was -12dB. Since I had no way in software to change this, I went ahead and ran the cal. 

Under the settings menu. I cannot select "Control input mixer/volume', and "Input Volume" is greyed out and set to 0.250. 

Dennis H's post of 9/14/09 states:
"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."

This is what I'm trying to accomplish. Is it possible with my setup?

Thanks,

Russ


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Under the settings menu. I cannot select "Control input mixer/volume', and "Input Volume" is greyed out and set to 0.250.


The Input Volume control should activate if you select the eMu in the top Input and Output device windows, and change the lower window to Speaker and Line In.


Regards,
Wayne


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## rsritchey (Jan 27, 2010)

I believe that's how I had it set, but I'll confirm when I get home tonight. Do you use an EMU as your soundcard? If so, could you confirm that you can adjust the input levels in software?


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## Wayne A. Pflughaupt (Apr 13, 2006)

No, I don’t have an E-Mu. If it doesn’t show up in the window, there might be a compatibility issue between it and your operating system. If all else fails, up the gain control. That’s what it’s there for. You can always mark your setting with a Sharpie or something for future reference.

Besides, Dennis didn’t say what he was using for a mic. If he was using the Radio Shack meter, it has a line level output, which is a fairly hot signal. So he’d be able to get away with leaving the gain all the way down.

Regards,
Wayne


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## rsritchey (Jan 27, 2010)

Thanks for your help Wayne. 

It looks like the only way to adjust input levels is through the knob on the front of the Tracker Pre. I'll just have to keep track of the settings from measurement to measurement.

Regards,

Russ


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