Related tutorials:

• Playing background music

Sounds are very important to put some life into your application, usually the game.

What is the difference between short sounds and long sounds? Let’s say, you are making a game and there is a constantly looping (or changing the track once played) background music. This is certainly not a short sound and it will be discuss somewhere else. You can play a short sound once you press the button, hit the wall, an alert occurred, a weapon was used… This kind of sounds could also be played as a background music but there is one problem with playing few background musics on iPhone… The iPhone processor can deal only with one background music and many sounds, that’s why music played from your library on iPhone / iPod touch stops once any app starts to play background music.

Sounds cannot be longer the 30 seconds and you should convert them before adding to the project. How? Open Terminal application on your mac and use the afconvert:

/usr/bin/afconvert -f caff -d LEI16 input_file output_file

Example:

MBP-Krzysiek:~ Krzysiek$ /usr/bin/afconvert -f caff -d LEI16 /Users/Krzysiek/Desktop/samlpe\ music.mp3 /Users/Krzysiek/Desktop/samplemusic.caf

SystemSound

SystemSound plays any sound without affecting the background music of your application or music from iPod. It doesn’t provide any volume control, user can control volume by changing the master volume of the device. Before you start to code, you need to add an AudioToolbox framework to your project (if you don’t know how: ctrl-press any existing .framework, Reveal in Finder and drag and drop the AudioToolbox.framework to the Frameworks group).

Add a new class (name it sounds) to your project, choose NSObject subclass, but in fact, it doesn’t metter, if you replace all code in header and implementation file with these provided by me:

sounds.h

#import <Foundation/Foundation.h>
#import <AudioToolbox/AudioServices.h>

@interface sounds : NSObject {
	SystemSoundID soundID;
}
-(id) initWithContentsOfFile:(NSString *)path;
-(void)play;
@end

sounds.m

#import "sounds.h"

@implementation sounds
-(id) initWithContentsOfFile:(NSString *)path {
	self = [super init];
	if (self != nil) {
		NSURL *filePath = [NSURL fileURLWithPath:path isDirectory:NO];
		AudioServicesCreateSystemSoundID((CFURLRef)filePath, &soundID);
	}
	return self;
}
-(void)play {
	AudioServicesPlaySystemSound(soundID);
}
-(void)dealloc {
	AudioServicesDisposeSystemSoundID(soundID);
	[super dealloc];
}
@end

Import sounds.h (#import “sounds.h”) to any class (for example game.h) that will call sounds class to play a short sound. If the sound is played many times (like in most cases) add in header the object:

	sounds *mySound;

or

	sounds *mySound1, *mySound2, *mySound3; // , *mySound4 ... *mySound(n)

or

	sounds *mySound[3];

	mySound = [[sounds alloc] initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"myFunnySound" ofType:@"caf"]];

AVAudioPlayer

AvAudioPlayer plays any sound also without affecting the background music of your application, but it terminates the music from iPod. It gives the user the ability to control the volume within the application (if you provide a slider or any other interface to adjust the volume), or by changing the master volume of the device. Before you can use AVAudioPlayer you need to add AVFoundation.framework to your project.

Please note:
Using AVAudioPlayer is much simpler than SystemSounds. I implemented a class to use SystemSounds, because I don’t like using such a long method names (AudioServicesPlaySystemSound) when they are called frequently. To play sound with AVAudioPlayer I need only 2-3 lines of code so writing a class to handle it is pointless and useless for me.

To prepare the sound you need to repeat almost the same steps I told in SystemSounds. Let’s add in the header file of your class an instruction to import AVAudioPlayer.h framework:

#import <AVFoundation/AVAudioPlayer.h>

And the AVAudioPlayer object with our sound:

	AVAudioPlayer *myAVsound;

To start, and assing the sound file you also need to provide a path to that resource:

	myAVsound = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"myFunnySound" ofType:@"caf"]  ] error:NULL];

The method to play this sound couldn’t be simpler:

	[myAVsound play];

… and to adjust the volume:

	myAVsound.volume = 0.6;

The volume can be adjusted also during the sound is being played.

Please note:
The given volume should be a number from range <0.0,1.0>. When the volume=0, user won’t hear the sound at all (O RLY?). You could also set the volume=2.0 or 10.0 but be careful. Instead of the louder sound you can get an unbearable to here noise (especially when the sound is saved in low quality), it can be harmful to user’s ear, if he uses headset, or can damage the device’s speaker.

BTW:
AVAudioPlayer allows you to loop the sound (myAVsound.numberOfLoops = 2;).

Please note:

I’ve heard many problems with playing the sounds with iPhone Simulator, in other words, the project cannot be compiled to run on iPhone Simulator. I personally have this problem, but as long as I participate in iPhone Developer program. I guess (but I’m not sure) that is because of computer you use. I use MacBook Pro Mid/Late 2007 (MA895) 2.2 GHz. As long as I know, this problem doesn’t occur on MacBook Pros shipped with unibody enclosure.

That’s almost everything you need to know about short sounds. You can download the sample project below.It allows you to play a sound (included in the project) via SystemSound and via AVAudio Player with slider adjusting the volume.

Download the project

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