How to control hardware mic input gain/level on iPhone?

Question

My audio-analysis function responds better on the iPad (2) than the iPhone (4). It seems sensitive to softer sounds on the iPad, whereas the iPhone requires much louder inpu

Answer 1

On ios6+ you can use AVAudioSession properties

        CGFloat gain = sender.value;
        NSError* error;
        self.audioSession = [AVAudioSession sharedInstance];
        if (self.audioSession.isInputGainSettable) {
            BOOL success = [self.audioSession setInputGain:gain 
                                                     error:&error];
               if (!success){} //error handling
        } else {
            NSLog(@"ios6 - cannot set input gain");
        }               

On ios5 you can get/set audio input gain properties using AudioSession functions

    UInt32 ui32propSize = sizeof(UInt32);
    UInt32 f32propSize = sizeof(Float32);
    UInt32 inputGainAvailable = 0;
    Float32 inputGain = sender.value;


    OSStatus err = 
        AudioSessionGetProperty(kAudioSessionProperty_InputGainAvailable
                            , &ui32propSize
                            , &inputGainAvailable);

    if (inputGainAvailable) {
    OSStatus err = 
        AudioSessionSetProperty(kAudioSessionProperty_InputGainScalar
                             , sizeof(inputGain)
                             , &inputGain);
    } else {
        NSLog(@"ios5 - cannot set input gain");
    }
    OSStatus err = 
        AudioSessionGetProperty(kAudioSessionProperty_InputGainScalar
                              , &f32propSize
                              , &inputGain);
    NSLog(@"inputGain: %0.2f",inputGain);

(error handling omitted)

As you are interested in controlling input gain, you may also want to disable automatic gain control by setting the audio session mode to AVAudioSessionModeMeasurement (ios5+6)

[self.audioSession setMode:AVAudioSessionModeMeasurement
                     error:nil];
NSLog(@"mode:%@",self.audioSession.mode);

These settings are fairly hardware-specific so availability cannot be assumed. For example, I can alter the gain on iPhone3GS/ios6 and iPhone4S/ios5.1, but not on ipadMini/ios6.1. I can disable AGC on the iPhone3G and the iPad mini, but not the iPhone4S.

Answer 2

I think this can help you : http://www.stefanpopp.de/2011/capture-iphone-microphone/