Microphone input gets -120.0 dB after call interruption

(this is my first question so i hope i give enough information) i am developing an application that samples the microphone input continuously with a timer. during normal operation everything is ok, if i close开发者_如何学运维 the app with the home button and then return to it i may see a few iterations with microphone input of -120.0 but then it start measuring correctly again.

however if i place a call to the phone (and not answer) the microphone input measures -120.0 all the time.

any ideas?

You need to set an audio session with an audio session interrupt handler. Then you can cleanly stop and restart your audio queue or audio unit (etc.) after the call interruption in the handler callbacks. See Apple's Audio Session documentation.