How can I mute microphone input volume using AudioUnits? - ios

Question

I'm using AudioUnits to record and play sound . It's part of a soft phone.
This is my initialisation:
AudioStreamBasicDescription audioFormat;
audioFormat.mSampleRate = 8000;
audioFormat.mFormatID = kAudioFormatULaw;
audioFormat.mFormatFlags = kAudioFormatFlagIsPacked | kAudioFormatFlagIsSignedInteger;
audioFormat.mFramesPerPacket = 1;
audioFormat.mChannelsPerFrame = 1;
audioFormat.mBitsPerChannel = 16;
audioFormat.mBytesPerPacket = 2;
audioFormat.mBytesPerFrame = 2;
status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, kInputBus, &audioFormat, sizeof(audioFormat));
AURenderCallbackStruct callbackStruct;
callbackStruct.inputProc = recordingCallback;
callbackStruct.inputProcRefCon = (__bridge void *)(self);
status = AudioUnitSetProperty(audioUnit,
kAudioOutputUnitProperty_SetInputCallback,
kAudioUnitScope_Global,
kInputBus,
&callbackStruct,
sizeof(callbackStruct));
During the recording process I'm using a callback to process the sound:
static OSStatus recordingCallback(void *inRefCon,
AudioUnitRenderActionFlags *ioActionFlags,
const AudioTimeStamp *inTimeStamp,
UInt32 inBusNumber,
UInt32 inNumberFrames,
AudioBufferList *ioData)
Now at some point I would like to mute the microphone. After googling, I found this as a solution:
-(void) setMuteOn {
AudioUnitParameterValue volume = 0.0;
AudioUnitSetProperty(audioUnit, kMultiChannelMixerParam_Volume, kAudioUnitScope_Input, 1, &volume, 0);
}
But it doesn't work. Perhaps I need to do some kind of refresh on my audioUnit, I don't know. Any help would be great.

Answer 1

Actually it was easier than I thought. In the callback method I just overwrote those sound buffers with silence. In my case I was using ULAW compression, so just filled my array with 0xFF
The microphone was still recording, but I stopped using the data.

Answer 2

You could do the following which I think is a little cleaner.
-(BOOL)microphoneInput:(BOOL)enable;
{
UInt32 enableInput = (enable)? 1 : 0;
OSStatus status = AudioUnitSetProperty(
ioUnit,//our I/O unit
kAudioOutputUnitProperty_EnableIO, //property we are changing
kAudioUnitScope_Input,
kInputBus, //#define kInputBus 1
&enableInput,
sizeof (enableInput)
);
CheckStatus(status, #"Unable to enable/disable input");
return (status == noErr);
}