Some of you may have already discovered that if you use one of our apps on an iPad running iOS 9.3.1, the built-in microphone does not work as expected. For example, if you run SoundMeter and press start, you see a reading of “-inf” rather than something more reasonable, like “52.5 dB”.
You may have also noticed that if you set the mic input gain to Mid, rather than Low, that you get a reading, but it is very low, like “-22.0 dB”. If you keep the input gain set at High, then you should see similar results to what you saw before the recent updates to iOS.
We have recently discovered that, while running SoundMeter, if you then connect a headset microphone and disconnect it, the built-in microphone readings will behave just as they have since the introduction of iOS 8.0. In other words, connecting and disconnecting a headset microphone returns things to normal for the built-in mic.
If you rely on SoundMeter, or one of our other apps, for regular sound level measurements, you might want to consider holding off on updating iOS until a solution is available. For those who have already updated, the workaround of connecting and disconnecting a headset microphone offers a solution for continuing to work with the built-in microphone as before.
Because of the change in input signal level that occurs with the built-in microphone with the connection and subsequent disconnection of a headset microphone, this is a problem that we cannot fix with an update to our apps. It must be corrected by Apple (we have already filed a detailed bug report with Apple). It does not just affect our apps, but potentially any audio app that uses the built-in microphone with the input gain set to anything less than the maximum value. (We have verified that measurement apps from other developers that rely on the iPad’s built-in microphone can also be affected by this.)
We have recently verified this issue, and the workaround, with 5 different iPad models and believe it to be of general concern for all iPad models that support iOS 9.3. We are not aware of any similar issues with iPhone or iPod touch.