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.

How Files are Parsed and Applied

The maximum resolution of input files that is supported is 1/12th octave, for a maximum of 12 octaves. Files with more resolution will be processed to average the values within each 1/12th octave point. 

Then, depending on the module, the resolution may again be compressed. For example, RTA will process the compensation data appropriately for 1/3 or 1/1 octave mode.

To see how your data file was processed, go to FFT, Settings, and switch from Low to Full mode. When you return to the main screen, before pressing play you will be able to see the actually plot if you scroll down.

Here is an example file to download.

Using iCloud to Import Microphone Compensation Files

Using iCloud is the easiest way to import files, and provides more advantages such as the ability to share files between devices. First, setup iCloud by following these instructions. Then, on your computer, navigate to the iCloud folder "calibration", under public. If the folder does not exist, create it. 

Screen Shot 2016-02-17 at 10.12.41 AM

Next, copy your compensation file to the calibration folder. The next time you go to AudioTools, Settings->Microphone Setup, select your microphone by tapping the small "i", and then tap the "Calibration File" button, you will see the file that you added from your computer. 

Select the file and the calibration will be applied.

Using Dropbox to Upload Microphone Compensation Files

Using Dropbox requires you to have a Dropbox account, and to link that account to AudioTools. Once you have Dropbox setup, any calibration files that are stored in the correct folder on your Dropbox will automatically be available 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, tap the "Cloud File Storage" button, and then select the Dropbox option on the control. The tap the "Link" button to complete the process.

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 


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

Now go to the Settings->Microphone page, and select a microphone to calibrate by tapping the i in the circle on the right. Tap the Calibration File button to open the Calibration Files screen.

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.

  • 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.

  • 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.