Tutorial: The first step to making a ‘Talking’ iPhone app, chipmunkifying your voice!

Yah, I invented a word, “chipmunkifying”, or to make your voice sound like a chipmunk. Why? ‘Talking’ apps are all over the place in the iPhone app store, there’s a talking tom cat, talking bird, talking hippo, talking giraffe, whatever animal you can think of… Basically what those apps do is, you say something, and then the animal will repeat it, in this chipmunk like voice. Oh, you can poke, tickle, hit it too, or whatever…

Oh, I am using Cocos2D as my game engine. So, begin by creating a project using the Cocos2D application template. If you are not familiar with Cocos2D, you can go to its website for instructions on how to download and install it.

Well, so the first step to a ‘Talking’ app is of course, it has to record what you say.

I’ll be using AVAudioRecorder to record my voice, it’s really simple to set up, just follow the intructions on this blog by Jake Wyman. But he uses the iPhone SDK, while I will be using Cocos2D. So just follow his tutorial up to the part of adding frameworks:

From your XCode interface you are going to select the Frameworks folder, ctl>click and choose ADD and then select Existing Frameworks… Then choose both the CoreAudio.Framework and the AVFoundation.Framework

And after we have done that, some coding… Rather copy paste some code from Jake’s.

First create a NSObject class, named AudioController.

Import AVFoundation and CoreAudio:

#import <AVFoundation/AVFoundation.h>
#import <CoreAudio/CoreAudioTypes.h>

Set up AudioController as a AVAudioRecorderDelegate. And declare an AVAudioRecorder, and a string for recordedTmp (the file path where we will temporarily store our audio).

@interface AudioController : NSObject <AVAudioRecorderDelegate>

{   AVAudioRecorder * recorder;

   NSString *recordedTmpFile;


We instantiate an AVAudioSession in a function called initAudioController (basically the code inside Jake’s viewDidLoad):

– (void) initAudioController
{   //Instanciate an instance of the AVAudioSession object.
    AVAudioSession * audioSession = [AVAudioSession sharedInstance];
    //Setup the audioSession for playback and record.
    //We could just use record and then switch it to playback leter, but
    //since we are going to do both lets set it up once.
    [audioSession setCategory:AVAudioSessionCategoryPlayAndRecord error: &error];
    //Activate the session
    [audioSession setActive:YES error: &error];

And then our record function:

-(void) record
{   NSMutableDictionary* recordSetting = [[NSMutableDictionary alloc] init];
   [recordSetting setValue :[NSNumber numberWithInt:kAudioFormatAppleIMA4] forKey:AVFormatIDKey];
   [recordSetting setValue:[NSNumber numberWithFloat:44100.0] forKey:AVSampleRateKey];
   [recordSetting setValue:[NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey];
   recordedTmpFile = [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent: [NSString stringWithString: @”recording.caf”]]];
   recorder = [[ AVAudioRecorder alloc] initWithURL:recordedTmpFile settings:recordSetting error:&error];
   [recorder setDelegate:self];
   [recorder prepareToRecord];      
   [recorder record];

And now, to play whatever recorded in a chipmunk voice. In Jake’s project he uses AVAudioPlayer to play his sound, but that isn’t going to work for me, because AVAudioPlayer doesn’t allow me to change the playback speed.

So instead of using that, I will be using CocosDenshion’s CDSoundEngine. I am reading Chapter 9 : Playing Sounds With CocosDenshion of Cocos2d for iPhone 0.99 Beginner’s Guide:

According to Pablo Ruiz, we need to import more frameworks to get CDSoundEngine working:

… include OpenAL and AudioToolbox frameworks in your project.

More imports:

#import “cocos2d.h”
#import “CocosDenshion.h”

And then declare a CDSoundEngine:

CDSoundEngine *soundEngine;

In initAudioController function, we initialize the soundEngine.

soundEngine = [[CDSoundEngine alloc] init: kAudioSessionCategory_PlayAndRecord];

NSArray *defs = [NSArray arrayWithObjects: [NSNumber numberWithInt:1],nil];
[soundEngine defineSourceGroups:defs];

And then we play:

-(void) play
{   NSString *filePath = [NSTemporaryDirectory() stringByAppendingPathComponent: [NSString stringWithString: @”recording.caf”]];

   [soundEngine loadBuffer: recordedTmpFileIdx filePath: filePath];
   [soundEngine playSound: recordedTmpFileIdx sourceGroupId: 0 pitch: 2.0f pan: 0.0f gain: 1.0f loop: NO];   

Take note of the pitch property: it says 2.0f. What does it mean? The setting for normal pitch is 1.0f, if you increase its value, you get a higher pitch, also known as a chipmunked voice, if you decrease the pitch, you get this low kind of creepy voice.

We also need to make a function for stopping the recording and then start playing:

-(void) stopRecording
{   [recorder stop];
    [self play];

And then we make a function for unloading the AudioController:

– (void) unloadAudioController
{   NSFileManager * fm = [NSFileManager defaultManager];
    [fm removeItemAtPath:[recordedTmpFiles [0] path] error:&error];
[recorder dealloc];
    recorder = nil;
   [soundEngine release];


Okay, now we have AudioController done, it’s time to call it in our HelloWorld scene. Yes. the HelloWorld that comes with the default template. I also added a BOOL isRecording to keep trakc if we are recording or playing.


#import “cocos2d.h”
#import “AudioController.h”

// HelloWorld Layer
@interface HelloWorld : CCLayer
{    AudioController *audioLayer;

     BOOL *isRecording;

+(id) scene;


For HelloWorld.m, in init, add swallowedTouches and change the “Hello World” label to “Say something…” or “Speak!” or “Talk to me” or whatever.

[[CCTouchDispatcher sharedDispatcher] addTargetedDelegate:self priority:0 swallowsTouches:YES];
CCLabel* label = [CCLabel labelWithString:@”Say something…” fontName:@”Marker Felt” fontSize:32];

Also in init, initialize audioLayer, and set isRecording to NO

audioLayer = [[AudioController alloc] init];
[audioLayer initAudioController];

isRecording = NO;

And then, since I am lazy to add buttons, the user simply taps the iPhone, anywhere on the iPhone once, to record and then tap again to stop recording and play the audio.

– (BOOL)ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event

{    if(isRecording)

    {    [audioLayer stopRecording];

           isRecording = NO;



    {       [audioLayer record];

            isRecording = YES;



And in HelloWorld’s dealloc add:

[audioLayer unloadAudioController];

And that’s it 🙂

You can record your voice and play to sound like a chipmunk 🙂

For any questions (or if you find any errors), feel free to contact me through Twitter, here, email, Facebook or whatever.

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