# Using soundcard output calibration with USB microphone



## mcmahongg (Aug 6, 2010)

If one has a calibration curve for the soundcard (obtained e.g. using a calibrated spectrum analyser) is it possible to use this to correct the speaker drive voltage when working with a USB microphone.

Using this curve in REW soundcard calibration doesn't seem to be the way to go, as the input comes via USB rather than via soundcard input. 

Suppose one combined the output calibration curve with the USB microphone manufacturers calibration curve and used that in place of the original microphone curve - would that work?


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## AudiocRaver (Jun 6, 2012)

mcmahongg said:


> If one has a calibration curve for the soundcard (obtained e.g. using a calibrated spectrum analyser) is it possible to use this to correct the speaker drive voltage when working with a USB microphone.
> 
> Using this curve in REW soundcard calibration doesn't seem to be the way to go, as the input comes via USB rather than via soundcard input.
> 
> Suppose one combined the output calibration curve with the USB microphone manufacturers calibration curve and used that in place of the original microphone curve - would that work?


We have two separate variables, sound card input curve and sound card output curve. The only way to accurately eliminate one is with an additional reference piece of hardware, i.e. either a calibrated output you can use to play a test sweep into your input, eliminating it as a variable, or playing a test sweep from your output into another calibrated input, eliminating that as a variable. Without that, I don't see how it is possible to know what the sound card's output response is. This is a minor drawback of using a USB mic.

Edit: Beg pardon, brain is working slow today, I misunderstood your post, that is pretty much what you are suggesting, and yes, properly combining the known output response curve with the mic calibration curve, or something to that effect, would give you the result you are after.


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## mcmahongg (Aug 6, 2010)

Thanks for your help! I'll try that.


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## JohnM (Apr 11, 2006)

No reason not to load that second cal file as the soundcard cal though, then REW will take care of combining the two.


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## AudiocRaver (Jun 6, 2012)

Yes, clearly the easy/right way to do it rather than trying to manually combine that data with the mic calibration data (the hard way, error-prone, and probably exactly what I would try on a day I was short on sleep and not thinking straight - doh!:doh.

Thanks, John.:T


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## mcmahongg (Aug 6, 2010)

Thanks John!

On my setup I notice that the indicators at the bottom of the REW screen indicate '16 bit' rather than the expected '24 bit' - wonder why?


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## JohnM (Apr 11, 2006)

Java drivers only provide 16-bit audio data. 24-bit data is available under Windows using ASIO drivers (as long as the ASIO driver provides it). Makes no difference for acoustic measurements though, the dynamic range of the captured audio signals is comfortably handled with 16 bits.


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## mcmahongg (Aug 6, 2010)

Thanks John!


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