Reduce / decrease background ipod sound in my App - ios

Question

I need to make an application in iOS who make different sound like "beep" during her fonctionnement.
I have implemented interaction to background ipod with MPMusicPlayerController.
The probleme:
I do not hear the "beep" due to the volume of music from ipod.
I need to reduce the volume of the ipod but NOT reduce the volume of my application.
The tomtom application make that when the speaker give information about the direction to take. But I do not know how.
I have try this code:
- (void)playSoundCountDown{
NSError *errorObject = nil;
[[AVAudioSession sharedInstance]setCategory:AVAudioSessionCategoryAmbient error:&errorObject];
if (errorObject) {
NSLog(#"Error setting category! %#",errorObject);
}
NSString *path = [[NSBundle mainBundle] pathForResource:#"countDownFiveToOne" ofType:#"caf"];
theSound = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path] error:nil];
theSound.delegate = self;// (AVAudioPlayer *theSound;)
[theSound setVolume:0.4f];
[theSound play];
float volumeDecrease = 0.2f;
MPMusicPlayerController* iPodMusicPlayer = [MPMusicPlayerController iPodMusicPlayer];
[iPodMusicPlayer setVolume:volumeDecrease];
}
But "setVolume" reduce the volume of all sound of the device, included the sound of my app...
I need your help please.
Thanks.

Answer 1

Instead of decreasing the volume, try enabling ducking:
- (void)playSoundCountDown{
NSError *errorObject = nil;
[[AVAudioSession sharedInstance]
setCategory: AVAudioSessionCategoryAmbient
withOptions: AVAudioSessionCategoryOptionDuckOthers
error: nil];
NSString *path = [[NSBundle mainBundle] pathForResource:#"countDownFiveToOne" ofType:#"caf"];
theSound = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path] error:nil];
theSound.delegate = self;
[theSound setVolume:0.4f];
[theSound play];
}