A few months ago I saw this extremely addictive flash game/toy called ToneMatrix.

My immediate thought almost immediate thought (considering the game was so addictive and it took a while for me to think anything) was: “This would make quite possibly the coolest iPhone application ever.”

So my good friend, Anthony Mittaz, and I decided to have a crack at it but hit one immediate hurdle; however proficient an iPhone developer Anthony is, he hadn’t done anything to do with sound, and nor had I, in any language/framework, let alone on the iPhone. Let me tell you this: Apple’s documentation in this area is severely lacking. Tangent: well, almost all Apple documentation on specialised things is pretty sparse.

I think we spent about two weeks’ worth of nights reading documentation, source code (Cocoa, iPhone, Java, C, and others), and plain outright stabbing in the dark code-wise getting not much more than ugly pops and crackles. Whenever we thought we had a clean note working, we’d change the frequency to what should be another nice clean note, and would instead get ear-shattering screeches.

Nonetheless we persevered and were even able to come up with a nifty little piece of code that could take an array of frequencies and play them together in what could be made to sound like a pleasant chord.

Here is the relevant code:

Code

TonePlayer.h

#import <Foundation/Foundation.h>
#include <AudioUnit/AudioUnit.h>
#include <math.h>

#define kTonesAvailable 16
#define kOutputBus 0
#define kInputBus 1
#define kNumChannels 2

@interface TonePlayer : NSObject {
  AudioComponentInstance audioUnit;
  AudioStreamBasicDescription audioFormat;
  float phase[kTonesAvailable];
  float frequencies[kTonesAvailable];
}

-(OSStatus)start;
-(OSStatus)stop;
-(void)resetFrequencies;
-(void)cleanUp;
-(void)intialiseAudio;
@end

// Some C function headers to get arount compile errors while I refactor to be more readable
float phaseOffsetFromFrequency(float);
OSStatus RenderCallback(void*, AudioUnitRenderActionFlags*, const AudioTimeStamp*, UInt32, UInt32, AudioBufferList*);

TonePlayer.m

#import "TonePlayer.h"

typedef struct {
  @defs(TonePlayer);
} SinewaveDef;

@implementation TonePlayer

static float gSampleRate = 44100.;
static float notes[111]  = {
      8.1758, 8.6620, 9.1770, 9.7227, 10.3009, 10.9134, 11.5623, 12.2499, 
      12.9783, 13.7500, 14.5676, 15.4339, 16.3516, 17.3239, 18.3540, 19.4454,
      20.6017, 21.8268, 23.1247, 24.4997, 25.9565, 27.5000, 29.1352, 30.8677, 
      32.7032, 34.6478, 36.7081, 38.8909, 41.2034, 43.6535, 46.2493, 48.9994, 
      51.9131, 55.0000, 58.2705, 61.7354, 65.4064, 69.2957, 73.4162, 77.7817, 
      82.4069, 87.3071, 92.4986, 97.9989, 103.8262, 110.0000, 116.5409, 123.4708,
      130.8128, 138.5913, 146.8324, 155.5635, 164.8138, 174.6141, 184.9972, 
      195.9977, 207.6523, 220.0000, 233.0819, 246.9417, 261.6256, 277.1826, 
      293.6648, 311.1270, 329.6276, 349.2282, 369.9944, 391.9954, 415.3047, 
      440.0000, 466.1638, 493.8833, 523.2511, 554.3653, 587.3295, 622.2540, 
      659.2551, 698.4565, 739.9888, 783.9909, 830.6094, 880.0000, 932.3275, 
      987.7666, 1046.5023, 1108.7305, 1174.6591, 1244.5079, 1318.5102, 1396.9129, 
      1479.9777, 1567.9817, 1661.2188, 1760.0000, 1864.6550, 1975.5332, 2093.0045, 
      2217.4610, 2349.3181, 2489.0159, 2637.0205, 2793.8259, 2959.9554, 3135.9635, 
      3322.4376, 3520.0000, 3729.3101, 3951.0664, 4186.0090, 4434.9221, 4698.6363
  };

OSStatus    RenderCallback(void                          *inRefCon,
                           AudioUnitRenderActionFlags    *ioActionFlags,
                           const AudioTimeStamp          *inTimeStamp,
                           UInt32                        inBusNumber,
                           UInt32                        inNumberFrames,
                           AudioBufferList               *ioData)
{
  SinewaveDef* def = inRefCon;
  
  float *outL = ioData->mBuffers[0].mData;
  float *outR = ioData->mBuffers[1].mData;

  float wave, j;
  float freqs[kTonesAvailable];
  
  memset(freqs, 0.0f, sizeof(freqs));
  
  for (int i=0; i< inNumberFrames; i++){
    wave = 0.0f;
    j = 0.0f;
    
    for(int m = 0; m < kTonesAvailable; ++m) {
      if(def->frequencies[m] != 0) {
        if(freqs[m] == 0) freqs[m] = phaseOffsetFromFrequency(def->frequencies[m]);

        wave += 0.5 * sinf(def->phase[m]);
        def->phase[m] += freqs[m];
        
        ++j;
      }
    }
    
    wave /= j;
    
    *outL++ = wave;
    *outR++ = wave;
  }

  return noErr;
}

float phaseOffsetFromFrequency(float frequency) {
  return (float)(frequency * 2.0 * M_PI / gSampleRate);
}

-(void)resetFrequencies{
  memset(frequencies, 0.0f, sizeof(frequencies));
  memset(phase, 0.0f, sizeof(phase));
}

-(OSStatus)start{
  [self resetFrequencies];
  OSStatus status = AudioOutputUnitStart(audioUnit);
  
  // See http://www.phys.unsw.edu.au/jw/notes.html for note numbers
  frequencies[0] = notes[60]; // C
  frequencies[1] = notes[64]; // E
  frequencies[2] = notes[67]; // G
  
  sleep(1);
  
  frequencies[0] = notes[64];
  frequencies[1] = notes[67];
  frequencies[2] = notes[71];
  
  sleep(1);
  
  frequencies[0] = notes[74];
  frequencies[1] = notes[67];
  frequencies[2] = notes[70];
  
  
  return status;
}

-(OSStatus)stop{
  return AudioOutputUnitStop(audioUnit);
}

-(void)cleanUp{
  AudioUnitUninitialize(audioUnit);
}

-(AudioStreamBasicDescription)audioFormat{
  return audioFormat;
}

// Below code is a cut down version (for output only) of the code written by
// Micheal "Code Fighter" Tyson (punch on Mike)
// See http://michael.tyson.id.au/2008/11/04/using-remoteio-audio-unit/ for details
-(void)intialiseAudio{
  OSStatus status;
  
  // Describe audio component
  AudioComponentDescription desc;
  desc.componentType = kAudioUnitType_Output;
  desc.componentSubType = kAudioUnitSubType_RemoteIO;
  desc.componentFlags = 0;
  desc.componentFlagsMask = 0;
  desc.componentManufacturer = kAudioUnitManufacturer_Apple;
  
  // Get component
  AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);
  
  // Get audio units
  status = AudioComponentInstanceNew(inputComponent, &audioUnit);
  
  UInt32 flag = 1;
  // Enable IO for playback
  status = AudioUnitSetProperty(audioUnit, 
                  kAudioOutputUnitProperty_EnableIO, 
                  kAudioUnitScope_Output, 
                  kOutputBus,
                  &flag, 
                  sizeof(flag));

  // Describe format
        audioFormat.mSampleRate = gSampleRate;
  audioFormat.mFormatID = kAudioFormatLinearPCM;
  audioFormat.mFormatFlags = kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved;
  audioFormat.mFramesPerPacket = 1;
  audioFormat.mBytesPerPacket = sizeof(Float32);
  audioFormat.mBytesPerFrame = sizeof(Float32);
  audioFormat.mChannelsPerFrame = kNumChannels;
  audioFormat.mBitsPerChannel = 32;
  
  //Apply format
  status = AudioUnitSetProperty(audioUnit, 
                  kAudioUnitProperty_StreamFormat, 
                  kAudioUnitScope_Input, 
                  kOutputBus, 
                  &audioFormat, 
                  sizeof(audioFormat));
   
  // Set up the playback  callback
  AURenderCallbackStruct callbackStruct;
  callbackStruct.inputProc = RenderCallback;
  //set the reference to "self" this becomes *inRefCon in the playback callback
  callbackStruct.inputProcRefCon = self;
  
  status = AudioUnitSetProperty(audioUnit, 
                  kAudioUnitProperty_SetRenderCallback, 
                  kAudioUnitScope_Global, 
                  kOutputBus,
                  &callbackStruct, 
                  sizeof(callbackStruct));
  
  // Initialise
  status = AudioUnitInitialize(audioUnit);
}

@end

I really wish that I could remember how most of it worked, or, more importantly, the multitude of projects whose code we had to look at to get it working. If you recognise any of the code or can help add references on how people can build up a nice list of references for people to use if are following a similar pursuit.

If you are wondering what ever happened to the application we were building, it seems we weren’t the only ones who recognised the potential of ToneMatrix as an iPhone application. During the 2-3 weeks of us developing the sound generation code, about 5-6 ToneMatrix clones were added to the AppStore. While most were crap, there was one that we felt left little to be improved upon and we therefore recommend everyone goes and downloads Melodica. It’s just as addictive as the Flash version, only portable!

There have been a few posts asking how to access and manipulate the Keychain from within RubyCocoa but no answers supplied. As someone who is just getting into RubyCocoa (and Cocoa all together for that matter), I thought I’d document once and for all the process I took to get it working.

I am running on Leopard and while 10.5 is supposed to ship with BridgeSupport for most frameworks, the Security framework must have been left out. After playing around with using other frameworks (such as the AddressBook framework) and seeing how they were used, I did a bit of digging in the Apple Developer Documentation (incredible resource for anyone starting out) and stumbled across this gem: Generate Framework Metadata

After reading this, I was accessing the keychain within 5 minutes. Here’s how:

1. Run the following commands (first one will take some time):

   gen_bridge_metadata -f Security -o Security.bridgesupport
   mkdir -p /Library/BridgeSupport
   mv Security.bridgesupport /Library/BridgeSupport

2. Open an IRB session to test it:

   >> require 'osx/cocoa'
   => true
   >> OSX.require_framework 'Security'
   => true
   >> defined? OSX::SecKeychainAddGenericPassword()
   => "method"

Hoorah! Two steps! Well, one because the second one was just testing… Now go make password-able RubyCocoa application! I am not sure how to pull this off with deployable apps but I suggest your apps could ship with the file or run those commands on first-run or if the Security.bridgesupport file doesn’t exist. Note: I have not tested either of those scenarios, but I would guess the latter would be more reliable for cross-version development (i.e. Tiger + Leopard)

How to use these methods

# Require needed libraries

require 'osx/cocoa'
include OSX
require_framework 'Security'

# Set up some relevant variables

service = "Test Service"
account = "MyUsername"
password = "MyPassword"

# Add password to default keychain (first param)

SecKeychainAddGenericPassword(nil, service.length, service, account.length, account, password.length, password, nil)

# Finding a password in default keychain (first param)

status, *password = SecKeychainFindGenericPassword(nil, service.length, service, account.length, account)

# Password-related data
password_length = password.shift # => 10
password_data = password.shift # OSX::ObjcPtr object
password = password_data.bytestr(password_length)

# The last item is another OSX::ObjcPtr. I haven't figured 
# out how to cast or use this yet but will post when I've
# figured it out
keychain_item = password.shift

# Yay it works! You can also check the password exists
# in the Keychain Access utility. I've confirmed that
# this works
puts password # => "MyPassword"

[UPDATE 4/8/08]: Below is a fix for the REXML bug some people have been getting (myself included)

There is good news for anyone that has been getting the following error:

undefined local variable or method `trans’ for <UNDEFINED> … </>:REXML::Document
Usage: gen_bridge_metadata [options] <headers…>
Use the `-h’ flag or consult gen_bridge_metadata(1) for help.

There is a very simple fix. This is caused by a typo in the source of REXML. It’s such a massive bug I can’t believe it made it into the release of Ruby but i did some poking around and it looks like they renamed a method and didn’t change all references to it.

There are two ways to fix it—patching REXML; and patching gen_brige_metadata.

Personally I prefer patching the generator for peace of mind and have submitted the patch at http://bridgesupport.macosforge.org/trac/ticket/1, but I’ll show both fixes.

Patching gen_bridge_metadata

1. Open /usr/bin/gen_bridge_metadata and find the method definition for generate_xml (should be on line 1531)
2. Replace 0 in the xml_document.write() with -1 (both occurrences)
3. Save!

Patching REXML

1. Open /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rexml/document.rb
2. Find the line that has ‘if trans’ and change it to ‘if transitive’
3. Save!