General Calibration Information
For accurate results, you must calibrate AudioTools to your iPhone / Touch. The calibration procedure that you will use will depend on whether or not you are using iAudioInterface.

AudioTools keeps separate calibration values for all sources, including iAudioInterface inputs and outputs, and the built-in or headset mic on the iPhone / iPod Touch.

If you are not using iAudioInterface, skip ahead to the Detailed Calibration section.

These instructions are also available on our website.

iAudioInterface Calibration
If you have iAudioInterface, you were provided with calibration numbers to enter into the Trim fields for each calibration screen. Of course, if you have access to professional equipment, you can always check or override these numbers at any time. But for your first use, follow these instructions.

Enter the trim numbers that you have received with your iAudioInterface into the trim fields on the Microphone, Line Input, and Line Output pages.

Now, to complete your calibration, you just need to adjust for variations in your iPhone/iPod audio input and output levels. You use the iPhone / iPod Trim field for this. You only need to calibrate one of the three calibration screens to calibrate your device. You can use a microphone calibrator, calibrated generator, or calibrated level meter. If you use a level meter, make sure it is in RMS level meter.

If you have a microphone SPL calibrator, place it on the iAudioInterface mic and turn it on. Go to the Microphone Setup Screen on the Utility menu. Make sure External Microphone is selected. Now, tap the iPhone / iPod Trim + and - buttons until the SPL field reads the expected value. Exit this page, and you are done.

If you have a calibrated generator, or a signal source and a calibrated level meter, connnect it to the line input on the iAudioInterface, and select the Line Input Setup page from the Utility menu. Turn on the generator and note the output level, and make sure this level is in units of dBu. Now tap the dBu field on the screen and enter this value. Exit the page, you are done.

Detailed Calibration
These instructions are for calibrating the indivual settings for the microphone, line input, and line output. You can calibrate the microphone input and line input, even if you do not have iAudioInterface. There is no calibration for the output level if you are not using iAudioInterface.

Note that if you not using iAudioInterface, the iPhone Trim values are not used.

If you are using the built-in or headset mic our defaults should work well for you, since we get them from our database that has constants for iOS devices. However, if you have access to a calibrated SPL meter, you can adjust the calibration for more accurate readings.

Microphone Calibration
To calibrate the mic input, you will need either a microphone SPL calibrator, or a source of reasonably constant acoustic noise source, such as pink or white noise, and a calibrated reference SPL meter. Do not use a single frequency tone. If you are using acoustic noise, turn down the low frequency. This is important, since often there will be descrepencies in low frequency response of both the iPhone mic, and the reference SPL meter. The idea is to calibrate the center of the measurement window, especially since A-weighting rolls off low frequencies.

Now turn up the noise source until you read about 85dB SPL on the reference meter, or attach and turn on the SPL calibrator. Go to the Microphone Setup page, and make sure that you select the appropriate input: Internal Mic for the iPhone built-in mic or headset mic, External Mic for the iAI microphone, or External Line if you are calibrating your own microphone. Now, tap the SPL field and enter the observed value from the reference meter or the calibration value from the SPL calibrator. Exit the page, you are done.

Gain Setting

The Gain setting, if present, changes the gain of the iOS device input electronics. We recommend that you leave this set to the standard values. If you do wish to experiment with these, you will have to also set the Trim value, or the device will not be calibrated.

Gain can be set from 1.00 (maximum gain, best low SPL measurement) and 0.001 (lowest gain, provides the best high SPL measurements).

Line Input Calibration
If you are not using iAudioInterface, but you are using a dock-connector device that has a right-channel line input available, you can calibrate AudioTools to this device. Please note that many dock connector audio input devices use heavy compression as well as low-frequency filtering, so your results may vary. Check with the device manufacturer for more information.

To calibrate this device, connect a known level source to the device right input, and go to the Line Input Setup page on the Utility menu. AudioTools will detect that iAudioInterface is not installed, and will store the calibration figure separately from iAI calibration values. Tap the dBU field, and enter the known level which is being applied to the right channel line input. Exit the page, you are done.

Line Output Calibration
This calibration is only available for iAudioInterface. To calibrate the line output, connect the iAI line output to a level meter capable of reading to +14dBu balanced. Go to the Line Output Setup page on the Utility menu, and turn on the generator. Tap the Output Level dBU field and enter the value from the level meter. Exit the page, you are done.