AVAudioPlayerボリュームをフェードアウト

-(void)doVolumeFade 
{   
    if (audio.volume > 0.1) { 
        audio.volume = audio.volume - 0.1; 
        [self performSelector:@selector(doVolumeFade) withObject:nil afterDelay:0.5];    
	} else { 
        // Stop and get the sound ready for playing again 
        [audio stop]; 
        audio.currentTime = 0; 
        [audio prepareToPlay]; 
        audio.volume = 1.0; 
    } 
} 
 
 
//あるいは---------------------------------
while (theAudio_gLead1.volume > 0.0) {
	[self performSelector:@selector(reduceGLead1_Volume) withObject:nil afterDelay:0.1];
	NSLog(@"%f", theAudio_gLead1.volume);
}