I want to make an android application that allow user change the voice during phone call. For example: You are a man, you can change the voice to a woman or robot when talking over phone. It is like a funny prank.
I work around android's API and google for some days but still have no idea. Some one told is impossible but I see some app on google play can do: https://play.google.com/store/apps/details?id=com.gridmob.android.funnycall So I think there are some ways to do that.
I think about recording and play back by using AudioTracker but I have 2more problem: 1. I cannot mute the voice from phone call, so the phone only play my sound after processing 2. record and process will make a long delay (slow-realtime)
Can any one share some solution for this?
The app you linked isn't changing voices on the phone: it uses SIP (or similar) to place a call through the authors' servers and the voice changing happens there. That's why you only get a small number of free minutes of use before you have to pay them.
Yes it uses a sip server to do this process. The reason you cannot actually create an app that does this on the phone is because of two things. The first thing being, sound processing for the phone is locked. You can't unlock this because its strictly engineered through hardware not software. A pc can do this because it uses a standard sound card in which software can modify its frequencies. The second thing is phone manufactures are required to design their phones in a standard format. There are laws that force these companies to make it impossible to do any voice morphing. It is against the law to impersonate someone you are not, over any telephone network.
Hard way
You get the input voice, you use voice recognition to detect the words, then you use speech-to-text with your desired voice as output.
Less hard way
Sound processing: Changing frequencies, amplitude etc.
来源：https://stackoverflow.com/questions/14255967/change-voice-during-phone-call-android