Visual Microphone is a microphone monitor for iOS.
Visual Microphone may be used standalone or as an accessory to InterApp Audio Hosts apps like Garageband, allowing you to monitor your recording and adjust input gain and 3d sound position (currently much like stereo panning) in an interactive fashion.
Choose from 4 waveforms to monitor your input level and keep the dB of your input in sight.
Hint: Use headphones to avoid feedback loops
Visual Microphone costs $0.99 on the app store: