Calibrating the Built-in Microphone

Calibrating the mic

• If you already know the sensitivity of your built-in microphone (in Pa/FS), you can enter it directly in the Input Sensitivity text box of the calibration view and skip the rest of the calibration procedure.

1. Apply a known sound level to the built-in microphone of your iOS device.
   • You will need to calibrate your iOS device's built-in microphone relative to a calibrated sound level meter. If you have the Advanced or Pro Tool Set subscription, you can produce the reference signal with SignalScope's signal generator output connected to a loudspeaker (with a suitable amplifier in between, of course). You can then measure the sound level at a fixed location with your calibrated meter, remove the meter, and place your iOS device's microphone as close to the same measurement location as possible (and with the same orientation).
   • A 1 kHz tone at 94 dB is typically used for microphone calibration.
   • Performing a relative microphone calibration in a quiet, non-reverberant location is recommended.
   • Make sure the tone generator is turned on (in the Sig Gen tab) before proceeding to the next step.
   It might be a good idea to check the input signal in the Oscilloscope display to be sure the signal looks good and that there is no visible distortion of the waveform.
2. Open the I/O Device Configuration menu.
   • The I/O Configuration menu is directly accessible from the left side of the toolbar by tapping the microphone icon.
3. In the top row of the Input Options table, make sure the desired input device is selected (its name will be shown in parentheses).
4. Make sure the Device Units selection is set to Pa (pascals).
5. If you're using SignalScope's signal generator for a reference source, make sure Audio Play Through is switched off in the I/O Configuration menu.
6. Tap Calibrate.
7. The Calibration view displays the current measured input level as a text value as well as in a horizontal bar meter. If the current measured input level agrees with the reference sound level you have applied to the microphone (and there's no indication of input clipping), then you're done--your microphone already has the correct sensitivity applied.
8. Make sure your input is not clipping (you should not see the word "clip" displayed with a red box around it in the upper left-hand corner of the screen). If it is, you will need to decrease the level of your reference input signal. When the input signal is no longer clipping, the red box around the word "clip" will disappear.
9. Enter the reference sound level into the Ref. Input Level text box.
10. Wait a few seconds for the measured level to stabilize.
11. Tap the Calibrate button.
12. Confirm that you would like to Calibrate.
13. Now check to see that the measured input level closely matches the level of the reference signal. If it does, your microphone is properly calibrated.
    • Tapping the Calibrate button causes SignalScope to automatically calculate a proper sensitivity (of pascals relative to full scale input, or Pa/FS) for the microphone, based on the current measured input level and the Ref. Input Level value.
    • When working with the built-in microphone, the channel sensitivity and the device sensitivity are always the same.

• It is possible to adjust the input gain of the built-in microphone for some iOS devices. In this case, SignalScope offers Low, Mid, and High gain settings with nominal sensitivity values for each setting. This means that the gain can be changed and the level measurements retain their accuracy. User calibration can be performed for each gain setting independent of the others.

  The Gain setting can be used to adjust the measurement range. To measure higher signal levels, choose a lower gain setting.