Good Mic

GoodMic app lets you use your iPhone/iPad as a live microphone. Connect to your external speaker using either the lightning connector or Bluetooth and you're set to go. To sing karaoke, play the karaoke music using your favorite app or Web browser and just sing along.  GoodMic app automatically runs in the background and your voice will be mixed together with the karaoke music from other sources. You can adjust the volume of your voice, and turn the microphone on/off.