Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 7 Old 09-30-16, 08:53 AM Thread Starter
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Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs

Hi there,

I'm just getting started with using REW and practised taking some readings using an AKG CK61 ULS Capsule (probably not great to measure) but just to get used to the process - I'm getting there. I now have a Behringer ECM8000 - So two quick questions;

1) I have downloaded the calibration date from Behringer here
This provides an XLS (which I have converted to CSV). The headers included are Hz, dB, Phase. Are all these needed for the CSV, if so, which order and should the actual header row be included? I have also downloaded the Cross Spectrum Labs "Correction" file (.cal) for ECM8000 from the downloads section. This doesn't have headers and only seems to include Hz and dB values. Is this correct for CSV formatting also?

2) With the above in mind - which is considered most "accurate"? The one form Behringer or the one form Cross Spectrum Labs? Or, at least, which would you recommend I use for measurements?

Thanks in advance... Great software!
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post #2 of 7 Old 09-30-16, 10:52 AM
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Re: Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs

1) You can use all 3 columns of the Behringer file - no header is necessary. You can use the CSL file as is. The Behringer info appears to be for a 90 mic orientation (see chart below). The CSL file will be 0 mic orientation unless you have you have obtained files the both orientations from CSL. REW will use the phase data included with the Behringer file. If you use the CSL file REW will assume the phase is 0 across the full range. The impact of the phase information is not significant for any of the common home uses of REW.

2) For bass range or any measurements below 2000Hz the orientation of the mic and the file used does not make a significant difference. For jobs measuring over 2000Hz the best choice depends on the objective of the job. For full range EQ measurements the most popular choice is to use the CSL 90 cal file with the mic oriented in the vertical direction. If a 0 cal file is use for >2000Hz measurements the mic should be pointed in the general direction of the speaker being measured.

I hadn't seen this Behringer cal file before so I compared it to my CSL files for 90 mic orientation. It compared closely. I am pretty confident that this is the mic orientation used to create the Behringer cal data. I was curious as I did not see the orientation mentioned on the Behringer page. The small ripple in the Behringer 2-10 kHz range is probably just measurement variation? I would expect that it would not be consistent for all mics produced. It is only 0.5 dB so it is insignificant in any case. I would not be concerned with it, but would have preferred that is was smoothed out. You may want to do a comparison to the CSL 90 cal file if you have one.

Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs-ecm8000factory.png
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post #3 of 7 Old 09-30-16, 11:51 AM Thread Starter
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Re: Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs

Hey there... Thank you so much for such a quick reply. And really helpful stuff! I am looking for full range EQ measurements so I guess I'll start with the Behringer CSV file I downloaded (as that appears to be a 90 file as suggested) and take a reading from the same position, individually, for left and right speakers - I have Spirit Absolute 4Ps for a home studio mixing setup and the intent is to use the measurements to generate 'Filters Impulse Response as WAV' for use with a Convolution plugin in my DAW as described
.

However, without wanting to spark the debate over mic orientation that there seems to be, I did note that in the Room EQ Wizard (REW) Information Index the statement;
Quote:
REW author John Mulcany and Herb Singleton of Cross Spectrum Labs have long recommended 0 orientation for in-room frequency response measurements of main-channel speakers, and 90 for acoustics measurements.
This would imply that for "frequency response measurements" (I'm making the assumption this the same as "full range EQ measurements") I should perhaps utilise your second proposal; "0 cal file... for >2000Hz measurements the mic should be pointed in the general direction of the speaker being measured". I will try this also anyway and see what the results are but I just wondered, in this context, what "acoustic measurements" are? Is this measurement of Decay,Distortion, IR etc as opposed to Frequency Spectrum alone?

Probably a little off topic so sorry for my meandering... And thanks again for the help! Very much appreciated!
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post #4 of 7 Old 09-30-16, 02:56 PM
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Re: Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs

When EQ includes >2000 Hz filters we should be sure our mic cal file orientation is the same as the mic orientation we intend to use for the measurements. That means we can use either orientation. I would suggest that possibly the 0 orientation is slightly more robust in a case where the room has significant impact from reflections >2000 Hz. I suspect any difference is trivial except in rare cases however.

I assume 'acoustic measurements' is any measurement in a room that is not a quasi-anechoic measurement, so room EQ measurements at the LP are acoustic measurements.
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post #5 of 7 Old 09-30-16, 05:24 PM Thread Starter
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Re: Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs

Wonderful... Thanks again!
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post #6 of 7 Old 09-30-16, 09:17 PM
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Re: Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs


Keep in mind that the calibration files in question are only useful for the Behringer mics, and then only generally. You can see in the graph below how much response can vary from one sample of these mics to the next.



Variations Between ECM8000 Microphones


Bottom line, a generic calibration file can have its uses, mainly for seat-of-the-pants measurements, but you do not want to attempt any full-rage equalization based on an inaccurate measurement that you would get from a mic that does not have its own custom calibration file.

If you merely “want to get used to the process,” there’s no reason to use a generic calibration file that was generated for a different mic than the one you have. Your uncalibrated AKG capsule costs more than four times what an uncalibrated ECM8000 does, and as such probably has much flatter response out of the box. Loading it up with a generic ECM8000 calibration file will probably get frequency response measurements that are less accurate than you’d have with no calibration file at all.

Regards,
Wayne




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post #7 of 7 Old 10-02-16, 03:20 PM Thread Starter
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Re: Mic Calibration CSV Format - Behringer vs Cross Spectrum Labs

Hi there,

Thanks for the reply. And sorry for the delay in thanking you - I've been busy trying out measurements and applying both eq filters (in Fabfilter Pro Q2) and impulse filters (using Fog Convolver). Just to clarify, I am now using the ECM8000 (the AKG was just to test the process before my ECM8000 arrived) so, even though I understand the calibrations are just general, it certainly seems to reflect adequately.

I am currently using the recommended orientation of ~75 (i.e. 10-20 forward of vertical for use correcting LP measurements) and only applying filters from 20-500Hz after 1/6th smoothing - the corrections for higher seemed overly aggressive when referencing. While probably not perfect it does help tidy up the bottom end. I actually used three measurements (LP, LP + 3 inches left, LP + 3 inches right) and averaged the LP with the left then right offest; to produce a stereo Impulse Filter.

I'm not sure which of Fog Convolver (Impulse Filter) or FabFIlter Pro Q (Peak EQ Filter) is more accurate but it seemed the Impulse Filter less "colorful"?

Anyway, thanks for all your help again... I'll no doubt be back!
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