# Calibration file for Audio Technica AT4050



## _gl (Jun 23, 2011)

I've created a calibration file for the *Audio Technica AT4050* large-diaphragm studio condenser mic (attached) - mainly because I have one and it's already pretty flat. It's based on the published Frequency Response curve _(Omni, no roll-off, 20-20khz)_, AT say it's +-2db accurate:










Here's how the file matches the real curve:










For now I simply extended the lines beyond the published range - is there a better way?

And is the mic suitable for simple room measurments (at least for the lower freqs)?


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## _gl (Jun 23, 2011)

(pictures now work)


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## JohnM (Apr 11, 2006)

_gl said:


> For now I simply extended the lines beyond the published range - is there a better way?


Nope



> And is the mic suitable for simple room measurments (at least for the lower freqs)?


Looks pretty good to me.


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## _gl (Jun 23, 2011)

JohnM said:


> Looks pretty good to me.


Great, I read that small-diaphragm condensers are preferred - is that because they respond quicker in the higher freqs? And is a large-diaphragm condenser like the 4050 suited for the higher end?

BTW, if anybody wants to improve the calibration, be my guest (please upload changes here).


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## _gl (Jun 23, 2011)

This was my first calibration file, and even though the gridline points are pretty accurate, I had to do a lot of eye-balling for the intermediate values. It took a whole day (punch in some new points, save the cal file, reload in REW, compare visually, repeat) -a visual editor that can display the bitmap graph fullscreen and allow you to overlay and position points with the mouse would make this much faster and more accurate.

Are there any editors like that already out there? If not it would be an excellent addition for REW.

In fact if my graph had had a linear frequency distribution I could have done it all in Photoshop quite quickly, but as it didn't I had to keep checking the frequency position in REW of a visual point I wanted to include on the curve.


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## JohnM (Apr 11, 2006)

_gl said:


> Are there any editors like that already out there? If not it would be an excellent addition for REW.


SPL Copy can go straight from the graph image to a set of data, saves a lot of effort.


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## JohnM (Apr 11, 2006)

_gl said:


> Great, I read that small-diaphragm condensers are preferred - is that because they respond quicker in the higher freqs?


It is more down to smaller diaphragms remaining omni to higher frequencies, but the way they are mounted into the body also makes a big difference.


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## _gl (Jun 23, 2011)

JohnM said:


> SPL Copy can go straight from the graph image to a set of data, saves a lot of effort.


Very nice. However what amplitude range should I use? In my file I intuitively placed the flat portion at zero, with positive and negative offsets - was that right? SPL Copy doesn't allow that (only range 5-145db).


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## _gl (Jun 23, 2011)

Well, I wrote a quick program to apply the db offsets to get back to my flat=0 range - but actually the SPLcopy curve is much coarser than mine (even with 50 points) as it doesn't smoothe the pixel steps. It also doesn't take into account the thickness of the line it's tracing, so sometimes it traces it at one boundary, sometimes at the other, resulting in inaccuracies. Before you linked it I wondered about coding the same thing, but it's non-trival to be sure - but it could be imrpoved. Comparison (SPLcopy first):


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## JohnM (Apr 11, 2006)

_gl said:


> Very nice. However what amplitude range should I use? In my file I intuitively placed the flat portion at zero, with positive and negative offsets - was that right?


That is a sensible approach. For the soundcard cal REW sets the level at 1kHz to 0dB and offsets the remainder of the cal curve from there.


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