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Saving the Calibration
You will be prompted to save the calibration data when you exit Daqarta. The saved file will have an .ATN extension, but it is really an ordinary text file that can be viewed with Windows Notepad. Do not change this file manually. The file name will be Daqarta0.ATN for sound device 0 (as set by the Output Device control in the Start Preferences dialog), or Daqarta1.ATN for device 1 on a multi-card system, etc. On subsequent starts, Daqarta loads the file for whichever device has been specified.
The first line of the file gives the Windows version and the name of the device, followed by a line with manufacturer's ID, product ID, and driver version.
Next are two or three lines beginning with 'Duplex:' followed by the frequency, then four pairs of delay and drift values. (Drift values are shown in parentheses.)
Finally, there are separate sections for each calibrated control. Each section begins with the control's internal ID code (8 hexadecimal digits) and text name as it appears on the control. Beneath that there is a line for each functional step in the attenuator, giving the step number followed by the change in attenuation in dB from the step above it. The top (0th) step would naturally have zero change since there is no step above it, so that value is used instead to store the value set by Full-Scale Range Calibration dialog, which defaults to 1.00000 volt for each control.
Don't be alarmed if you see large jumps between step numbers. The "missing" lines are dummy steps that Windows sound card drivers include to make volume sliders appear to have finer control than they actually do.
The final step may have a special value of 255 dB which indicates no output.
Some steps may show oddball fractions of a dB, such as 4.38, but most will probably be somewhere near a multiple of 0.5 dB. Since most sound cards are used for entertainment only, and since human ears can't usually resolve changes finer than 1 dB (if that), there is not much incentive for sound card makers to strive for great precision in their attenuators.
Note that under Vista or Windows 7, 8, or 10, output controls use a "virtual mixer" that has no dummy steps and very fine step sizes at the top of the range. See Vista / 7 / 8 / 10 Issues for more information.
The most important thing is that the steps in the file accurately reflect the actual attenuation changes for the specified control on your sound card. If you have reason to believe this is not the case, you can save a copy of the .ATN file and repeat the calibration with a lower Dist Limit setting and/or a larger Frames count, and see if these values change.
Watch the spectrum especially during the first few steps of the calibration of the suspect control, after the distortion adjustment stage, to see if there are large remaining distortion peaks. Daqarta compares the sum of the 2nd and 3rd harmonics to the 2 kHz fundamental when determining distortion. If your system has unusually high peaks at other frequencies, it may pass the distortion test while still having too much distortion for accurate calibration. A lower Dist Limit setting may be needed so the tested harmonics will trigger a level reduction, reducing overall distortion.
Note that if you run Daqarta from a removable drive (such as a USB or "thumb" drive), any calibration you perform will only work with the sound card in use at the time. Moving the drive to a different system may result in uncalibrated operation.
If you need to run on different systems, save the calibration file using a Daqartan.ATN name where n is a single digit or letter that is different for each system. Then follow the Removable Drive with Multiple Systems instructions.
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