To my konwledge, the (voice call) audio data from micphone will be sent to PCM module for resampling, then to modem for coding before sending to air.I am here for asking in Android is it possible to intercept the audio data from PCM to modem? Because I want to encrypt them before sending out. Thank you ..
closed as off topic by Dave Tweed, Leon Heller, Brian Carlton, embedded.kyle, Connor Wolf Nov 2 '12 at 8:29
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You can record all Microphone audio using the Google API with your own software. Also - note that not all Android phones allow to capture incoming audio because of hardware limitations.
It will be better if your create your own Native application and use VoiP for your outbound audio, which is easily achieved because there are many VoiP application out there.
You cannot bypass the Google API because the driver level is protected by the Operating System. You application only has access to the API that the OS exposes to you. So if there is no API similar to "RedirectMIcrophoneToAuxAndThenToGSM" - then sorry you cannot do it- even using Native Java code.
I think the sole reason why NO phones allow you to replace the outgoing GSM audio with a altered one is it most likely illegal. TO prevent voice masking in terror, bullying, extortion, black mail,etc ...
Since you have a legitamate reason to encrypt your voice that must mean there is high financial benefit involved- So inherently you must make your own device to do it.