audio play 볼륨 조절하기

AVAudioPlayer *silentPlayer;
NSString *soundFile =[NSString stringWithFormat:@”%@/%@”, [[NSBundle mainBundle] resourcePath], @”1-welcome.wav”];
NSData *data = [NSData dataWithContentsOfFile:soundFile];

if (data){
NSError *outError;
silentPlayer = [[AVAudioPlayer alloc] initWithData:data error:&outError];
}else{
// trigger some error
}

silentPlayer.delegate = self;
silentPlayer.volume = 0.;
[silentPlayer play];