I need to create a slider that will adjust the gain of the current input
device. I’ve been studying Core Audio for clues or sample code on how to do
this, but haven’t found anything. I suspect I may need to create a mixer, but
am not sure (I’ve gotten about halfway through "Learning Core Audio” and that
reading so far, leads me to that conclusion). Here is some code that I’ve been
using to adjust the gain to a given level. If I want to set the gain to say,
75, the code works just fine to do that. I then wired it up to a slider to see
if it would work to continuously update the gain level as the slider knob is
moved, but what actually happens is that the gain is adjusted to 100 on the
first movement of the slider, and remains there until the slider is moved to
zero, at which point, the sound is muted. So here is the code, any help is most
appreciated.
AudioObjectPropertyAddress address;
AudioDeviceID deviceID;
OSStatus err;
UInt32 size;
UInt32 channels[ 2 ];
Float32 level;
SSAudioDevice * targetDevice = [self getTargetInputDevice];
address.mSelector = kAudioHardwarePropertyDefaultInputDevice;
address.mScope = kAudioObjectPropertyScopeGlobal;
address.mElement = kAudioObjectPropertyElementMaster;
deviceID = targetDevice.deviceID;
if(!targetDevice.ioLevel){
level = 0.5;
}
else{
level = targetDevice.ioLevel.floatValue / 100.0;
}
size = sizeof(deviceID);
err = AudioObjectGetPropertyData( kAudioObjectSystemObject, &address,
0, nil, &size, &deviceID );
if ( ! err ) {
address.mSelector =
kAudioDevicePropertyPreferredChannelsForStereo;
address.mScope = kAudioDevicePropertyScopeInput;
address.mElement = kAudioObjectPropertyElementWildcard;
size = sizeof(channels);
err = AudioObjectGetPropertyData( deviceID, &address, 0, nil,
&size, &channels );
}
if ( ! err ) {
Boolean hasProperty;
address.mSelector = kAudioDevicePropertyVolumeScalar;
address.mScope = kAudioDevicePropertyScopeInput;
address.mElement = kAudioObjectPropertyElementMaster;
hasProperty = AudioObjectHasProperty( deviceID, &address );
if(!hasProperty){
}
address.mElement = channels[ 0 ];
hasProperty = AudioObjectHasProperty( deviceID, &address );
if(!hasProperty){
}
address.mElement = channels[ 1 ];
hasProperty = AudioObjectHasProperty( deviceID, &address );
if(!hasProperty){
}
}
if ( ! err ) {
address.mSelector = kAudioDevicePropertyVolumeScalar;
address.mScope = kAudioDevicePropertyScopeInput;
size = sizeof(level);
address.mElement = kAudioObjectPropertyElementMaster;
err = AudioObjectSetPropertyData( deviceID, &address, 0, nil,
size, &level );
if(err){
address.mElement = channels[ 0 ];
err = AudioObjectSetPropertyData( deviceID, &address,
0, nil, size, &level );
address.mElement = channels[ 1 ];
err = AudioObjectSetPropertyData( deviceID, &address,
0, nil, size, &level );
}
}
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