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copied!<p>I'm also investigating this. I think the AudioQueue API is probably the way to go.</p> <p>Here's as far as I got, seems to work okay.</p> <p>File: BleepMachine.h</p> <pre><code>// // BleepMachine.h // WgHeroPrototype // // Created by Andy Buchanan on 05/01/2010. // Copyright 2010 Andy Buchanan. All rights reserved. // #include <AudioToolbox/AudioToolbox.h> // Class to implement sound playback using the AudioQueue API's // Currently just supports playing two sine wave tones, one per // stereo channel. The sound data is liitle-endian signed 16-bit @ 44.1KHz // class BleepMachine { static void staticQueueCallback( void* userData, AudioQueueRef outAQ, AudioQueueBufferRef outBuffer ) { BleepMachine* pThis = reinterpret_cast<BleepMachine*> ( userData ); pThis->queueCallback( outAQ, outBuffer ); } void queueCallback( AudioQueueRef outAQ, AudioQueueBufferRef outBuffer ); AudioStreamBasicDescription m_outFormat; AudioQueueRef m_outAQ; enum { kBufferSizeInFrames = 512, kNumBuffers = 4, kSampleRate = 44100, }; AudioQueueBufferRef m_buffers[kNumBuffers]; bool m_isInitialised; struct Wave { Wave(): volume(1.f), phase(0.f), frequency(0.f), fStep(0.f) {} float volume; float phase; float frequency; float fStep; }; enum { kLeftWave = 0, kRightWave = 1, kNumWaves, }; Wave m_waves[kNumWaves]; public: BleepMachine(); ~BleepMachine(); bool Initialise(); void Shutdown(); bool Start(); bool Stop(); bool SetWave( int id, float frequency, float volume ); }; // Notes by name. Integer value is number of semitones above A. enum Note { A = 0, Asharp, B, C, Csharp, D, Dsharp, E, F, Fsharp, G, Gsharp, Bflat = Asharp, Dflat = Csharp, Eflat = Dsharp, Gflat = Fsharp, Aflat = Gsharp, }; // Helper function calculates fundamental frequency for a given note float CalculateFrequencyFromNote( SInt32 semiTones, SInt32 octave=4 ); float CalculateFrequencyFromMIDINote( SInt32 midiNoteNumber ); </code></pre> <p>File:BleepMachine.mm</p> <pre><code> // // BleepMachine.mm // WgHeroPrototype // // Created by Andy Buchanan on 05/01/2010. // Copyright 2010 Andy Buchanan. All rights reserved. // #include "BleepMachine.h" void BleepMachine::queueCallback( AudioQueueRef outAQ, AudioQueueBufferRef outBuffer ) { // Render the wave // AudioQueueBufferRef is considered "opaque", but it's a reference to // an AudioQueueBuffer which is not. // All the samples manipulate this, so I'm not quite sure what they mean by opaque // saying.... SInt16* coreAudioBuffer = (SInt16*)outBuffer->mAudioData; // Specify how many bytes we're providing outBuffer->mAudioDataByteSize = kBufferSizeInFrames * m_outFormat.mBytesPerFrame; // Generate the sine waves to Signed 16-Bit Stero interleaved ( Little Endian ) float volumeL = m_waves[kLeftWave].volume; float volumeR = m_waves[kRightWave].volume; float phaseL = m_waves[kLeftWave].phase; float phaseR = m_waves[kRightWave].phase; float fStepL = m_waves[kLeftWave].fStep; float fStepR = m_waves[kRightWave].fStep; for( int s=0; s<kBufferSizeInFrames*2; s+=2 ) { float sampleL = ( volumeL * sinf( phaseL ) ); float sampleR = ( volumeR * sinf( phaseR ) ); short sampleIL = (int)(sampleL * 32767.0); short sampleIR = (int)(sampleR * 32767.0); coreAudioBuffer[s] = sampleIL; coreAudioBuffer[s+1] = sampleIR; phaseL += fStepL; phaseR += fStepR; } m_waves[kLeftWave].phase = fmodf( phaseL, 2 * M_PI ); // Take modulus to preserve precision m_waves[kRightWave].phase = fmodf( phaseR, 2 * M_PI ); // Enqueue the buffer AudioQueueEnqueueBuffer( m_outAQ, outBuffer, 0, NULL ); } bool BleepMachine::SetWave( int id, float frequency, float volume ) { if ( ( id < kLeftWave ) || ( id >= kNumWaves ) ) return false; Wave& wave = m_waves[ id ]; wave.volume = volume; wave.frequency = frequency; wave.fStep = 2 * M_PI * frequency / kSampleRate; return true; } bool BleepMachine::Initialise() { m_outFormat.mSampleRate = kSampleRate; m_outFormat.mFormatID = kAudioFormatLinearPCM; m_outFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked; m_outFormat.mFramesPerPacket = 1; m_outFormat.mChannelsPerFrame = 2; m_outFormat.mBytesPerPacket = m_outFormat.mBytesPerFrame = sizeof(UInt16) * 2; m_outFormat.mBitsPerChannel = 16; m_outFormat.mReserved = 0; OSStatus result = AudioQueueNewOutput( &m_outFormat, BleepMachine::staticQueueCallback, this, NULL, NULL, 0, &m_outAQ ); if ( result < 0 ) { printf( "ERROR: %d\n", (int)result ); return false; } // Allocate buffers for the audio UInt32 bufferSizeBytes = kBufferSizeInFrames * m_outFormat.mBytesPerFrame; for ( int buf=0; buf<kNumBuffers; buf++ ) { OSStatus result = AudioQueueAllocateBuffer( m_outAQ, bufferSizeBytes, &m_buffers[ buf ] ); if ( result ) { printf( "ERROR: %d\n", (int)result ); return false; } // Prime the buffers queueCallback( m_outAQ, m_buffers[ buf ] ); } m_isInitialised = true; return true; } void BleepMachine::Shutdown() { Stop(); if ( m_outAQ ) { // AudioQueueDispose also chucks any audio buffers it has AudioQueueDispose( m_outAQ, true ); } m_isInitialised = false; } BleepMachine::BleepMachine() : m_isInitialised(false), m_outAQ(0) { for ( int buf=0; buf<kNumBuffers; buf++ ) { m_buffers[ buf ] = NULL; } } BleepMachine::~BleepMachine() { Shutdown(); } bool BleepMachine::Start() { OSStatus result = AudioQueueSetParameter( m_outAQ, kAudioQueueParam_Volume, 1.0 ); if ( result ) printf( "ERROR: %d\n", (int)result ); // Start the queue result = AudioQueueStart( m_outAQ, NULL ); if ( result ) printf( "ERROR: %d\n", (int)result ); return true; } bool BleepMachine::Stop() { OSStatus result = AudioQueueStop( m_outAQ, true ); if ( result ) printf( "ERROR: %d\n", (int)result ); return true; } // A (A4=440) // A# f(n)=2^(n/12) * r // B where n = number of semitones // C and r is the root frequency e.g. 440 // C# // D frq -> MIDI note number // D# p = 69 + 12 x log2(f/440) // E // F // F# // G // G# // // MIDI Note ref: http://www.phys.unsw.edu.au/jw/notes.html // // MIDI Node numbers: // A3 57 // A#3 58 // B3 59 // C4 60 <-- // C#4 61 // D4 62 // D#4 63 // E4 64 // F4 65 // F#4 66 // G4 67 // G#4 68 // A4 69 <-- // A#4 70 // B4 71 // C5 72 float CalculateFrequencyFromNote( SInt32 semiTones, SInt32 octave ) { semiTones += ( 12 * (octave-4) ); float root = 440.f; float fn = powf( 2.f, (float)semiTones/12.f ) * root; return fn; } float CalculateFrequencyFromMIDINote( SInt32 midiNoteNumber ) { SInt32 semiTones = midiNoteNumber - 69; return CalculateFrequencyFromNote( semiTones, 4 ); } //for ( SInt32 midiNote=21; midiNote<=108; ++midiNote ) //{ // printf( "MIDI Note %d: %f Hz \n",(int)midiNote,CalculateFrequencyFromMIDINote( midiNote ) ); //} </code></pre> <p><strong>Update: Basic usage info</strong></p> <ol> <li><p>Initialise. Somehere near the start, I'm using initFromNib: in my code</p> <pre><code>m_bleepMachine = new BleepMachine; m_bleepMachine->Initialise(); m_bleepMachine->Start(); </code></pre></li> <li><p>Now the sound playback is running, but generating silence.</p></li> <li><p>In your code, call this when you want to change the tone generation</p> <pre><code>m_bleepMachine->SetWave( ch, frq, vol ); </code></pre> <ul> <li>where ch is the channel ( 0 or 1 )</li> <li>where frq is the frequency to set in Hz</li> <li>where vol is the volume ( 0=-Inf db, 1=-0db )</li> </ul></li> <li><p>At program termination</p> <pre><code>delete m_bleepMachine; </code></pre></li> </ol>

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