Using Microphone Calibration Files

Beginning with AudioTools v4.1, you can import a file containing frequency response data for a microphone, and that response curve will be applied to the microphone in many AudioTools modules.


The microphone response correction data will be applied in all modules that display frequency dependent information: RTA, FFT, Smaart Tools I Single Channel, and Transfer Function. Note that it will NOT be applied to basic SPL measurements.


AudioTools supports the pending AES standard for frequency response data (.frd) files, as well as most typical mic cal file formats. Specifically, files that conform to these rules may be read in:


  • File names must have either the .txt or .frd extension.
  • Files must contain ASCII characters (not binary data).
  • Lines must have a frequency value followed by a dB value, separated by a tab, comma, or blanks. Values may be in IEEE format, integer format, or floating point. Extra values are ignored.
  • Lines must be in order of ascending frequency.
  • Any number of data points may be present.
  • Lines beginning with '*' or ';', or blank lines, are skipped.


To import a calibration file into AudioTools, you can use Dropbox, or you can use a browser linked to AudioTools over WiFi.


Using Dropbox to Upload Microphone Compensation Files


Using Dropbox is the simplest option. It requires you to have a Dropbox account, and link that account to AudioTools. Once you have Dropbox setup, any calibration files in the correct folder on your Dropbox will automatically appear in AudioTools. See this page for more information about Dropbox.


First, you have to link AudioTools to your Dropbox folder. Start at the Settings->General page, and tap the Dropbox button.


When you have linked to Dropbox, just copy your mic compensation files to the public/calibration folder, under the app name. The full path for this folder is 


Dropbox/Apps/AudioTools/public/calibration 


If you don’t see the public or calibration folder, you will have to add them, one at a time, to your Dropbox. Then copy your file to the calibration folder.


Each time you open the Calibration Files screen, all of the files in that Dropbox folder will be automatically copied to your iOS device, and can be selected. If you need to change a file, just drop the modified file into the Dropbox folder and re-open the Calibration Files screen. The new file will overwrite the file on the iOS device.


Using a Browser to Upload the Calibration File


You can also link directly to AudioTools by using a web browser. Sometimes this can prove challenging, usually due to restrictions such as firewalls in your router.


To upload a file using a browser:

  • Create your calibration file according to the rules above.
  • In AudioTools, go to the Settings->Microphone screen, and tap the Cal File button (Calibration File button on iPad).
  • Tap the Files button to bring up the Files utility screen.
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  • On your computer, open a browser and enter the URL from the AudioTools Files screen (see above).
  • On your computer browser, select the "calibration" link. This is a very important step. You must change to the calibration folder, so the file will upload into that folder. The app only sees files in the “calibration” folder.
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  • After you have selected the calibration folder, click the "Choose" button on the browser, and navigate to the mic cal file that you wish to upload.
  • Click "Send" to transmit this file to AudioTools.
  • On AudioTools, tap "Done" to go back to the Calibration Files screen.
  • Tap the Reload button (rounded arrow) to refresh the screen.
  • Tap the mic cal file name, which should now be visible.
  • Tap "Apply". If the import is successful, you will see a message showing the number of data points imported.
  • The import is complete. Tap done to go back to the Calibration screen.


At any time, you can revert to the default configuration by tapping the "Default" button on the Calibration Files screen.


The name of the current calibration file (or the word "default") will appear on the Calibration screen.