iOS signal generation pattern not expected - ios

Question

I would like to generate the tone with wave pattern as below ( last mid point should be at the bottom tough as previous set.)
When after chaining the frequency from 44.44Hz to 45.89 Hz, it becomes
Even I have changed the buffer length from 1024 to 960 , it stills shows that the buffer length is still at 1024 . Hence, it causes the problem that some of the remaining tails displays the mid-point tail instead of bottom .
The below is my code
OSStatus RenderTone(
void *inRefCon,
AudioUnitRenderActionFlags *ioActionFlags,
const AudioTimeStamp *inTimeStamp,
UInt32 inBusNumber,
UInt32 inNumberFrames,
AudioBufferList *ioData)
{
// Fixed amplitude is good enough for our purposes
const double amplitude = 2.7171;
// Get the tone parameters out of the view controller
ToneGeneratorViewController *viewController =
(ToneGeneratorViewController *)inRefCon;
double theta = viewController->theta; //992 f0r 44.44 , 959 for 45.89
double theta_increment = viewController->sampleRate / viewController->frequency;
int increment = ceil(theta_increment);
NSLog(#"increment= %i" , increment);
const int channel = 0;
Float32 *buffer = (Float32 *)ioData->mBuffers[channel].mData;
int squareIndex = 0;
for (UInt32 frame = 0; frame < 401; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 401; frame < 419; frame++)
{
buffer[frame] = -amplitude;
}
for (UInt32 frame = 419; frame < 468; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 468; frame < 487; frame++)
{
buffer[frame] = -amplitude;
}
for (UInt32 frame = 487; frame < 536; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 536; frame < 555; frame++)
{
buffer[frame] = -amplitude;
}
for (UInt32 frame = 555; frame < 604; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 604; frame < 622; frame++)
{
buffer[frame] = -amplitude;
}
for (UInt32 frame = 622; frame < 671; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 671; frame < 690; frame++)
{
buffer[frame] = -amplitude;
}
for (UInt32 frame = 690; frame < 739; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 739; frame < 757; frame++)
{
buffer[frame] = -amplitude;
}
for (UInt32 frame = 757; frame < 806; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 806; frame < 825; frame++)
{
buffer[frame] = -amplitude;
}
for (UInt32 frame = 825; frame < 874; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 874; frame < 892; frame++)
{
buffer[frame] = -amplitude;
}
for (UInt32 frame = 892; frame < 941; frame++)
{
buffer[frame] = amplitude;
}
for (UInt32 frame = 941; frame < increment; frame++)
{
buffer[frame] = -amplitude;
}
squareIndex += 1.0;
if(squareIndex >= theta_increment) squareIndex-=theta_increment;
viewController->theta = theta;
void ToneInterruptionListener(void *inClientData, UInt32 inInterruptionState)
{
ToneGeneratorViewController *viewController =
(ToneGeneratorViewController *)inClientData;
[viewController stop];
}
#implementation ToneGeneratorViewController
#synthesize frequencySlider;
#synthesize playButton;
#synthesize frequencyLabel;
- (IBAction)sliderChanged:(UISlider *)slider
{
frequency = 45.9;
frequencyLabel.text = [NSString stringWithFormat:#"%4.1f Hz", frequency];
}
- (void)createToneUnit
{
// Configure the search parameters to find the default playback output unit
// (called the kAudioUnitSubType_RemoteIO on iOS but
// kAudioUnitSubType_DefaultOutput on Mac OS X)
AudioComponentDescription defaultOutputDescription;
defaultOutputDescription.componentType = kAudioUnitType_Output;
defaultOutputDescription.componentSubType = kAudioUnitSubType_RemoteIO;
defaultOutputDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
defaultOutputDescription.componentFlags = 0;
defaultOutputDescription.componentFlagsMask = 0;
// Get the default playback output unit
AudioComponent defaultOutput = AudioComponentFindNext(NULL, &defaultOutputDescription);
NSAssert(defaultOutput, #"Can't find default output");
// Create a new unit based on this that we'll use for output
OSErr err = AudioComponentInstanceNew(defaultOutput, &toneUnit);
NSAssert1(toneUnit, #"Error creating unit: %ld", err);
// Set our tone rendering function on the unit
AURenderCallbackStruct input;
input.inputProc = RenderTone;
input.inputProcRefCon = self;
err = AudioUnitSetProperty(toneUnit,
kAudioUnitProperty_SetRenderCallback,
kAudioUnitScope_Input,
0,
&input,
sizeof(input));
NSAssert1(err == noErr, #"Error setting callback: %ld", err);
// Set the format to 32 bit, single channel, floating point, linear PCM
const int four_bytes_per_float = 4;
const int eight_bits_per_byte = 8;
AudioStreamBasicDescription streamFormat;
streamFormat.mSampleRate = sampleRate;
streamFormat.mFormatID = kAudioFormatLinearPCM;
streamFormat.mFormatFlags =
kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved;
streamFormat.mBytesPerPacket = four_bytes_per_float;
streamFormat.mFramesPerPacket = 1;
streamFormat.mBytesPerFrame = four_bytes_per_float;
streamFormat.mChannelsPerFrame = 1;
streamFormat.mBitsPerChannel = four_bytes_per_float * eight_bits_per_byte;
err = AudioUnitSetProperty (toneUnit,
kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Input,
0,
&streamFormat,
sizeof(AudioStreamBasicDescription));
NSAssert1(err == noErr, #"Error setting stream format: %ld", err);
}
- (IBAction)togglePlay:(UIButton *)selectedButton
{
if (toneUnit)
{
AudioOutputUnitStop(toneUnit);
AudioUnitUninitialize(toneUnit);
AudioComponentInstanceDispose(toneUnit);
toneUnit = nil;
[selectedButton setTitle:NSLocalizedString(#"Play", nil) forState:0];
}
else
{
[self createToneUnit];
// Stop changing parameters on the unit
OSErr err = AudioUnitInitialize(toneUnit);
NSAssert1(err == noErr, #"Error initializing unit: %ld", err);
// Start playback
err = AudioOutputUnitStart(toneUnit);
NSAssert1(err == noErr, #"Error starting unit: %ld", err);
[selectedButton setTitle:NSLocalizedString(#"Stop", nil) forState:0];
}
}
- (void)stop
{
if (toneUnit)
{
[self togglePlay:playButton];
}
}
- (void)viewDidLoad {
[super viewDidLoad];
[self sliderChanged:frequencySlider];
sampleRate = 44100;
OSStatus result = AudioSessionInitialize(NULL, NULL, ToneInterruptionListener, self);
if (result == kAudioSessionNoError)
{
UInt32 sessionCategory = kAudioSessionCategory_MediaPlayback;
AudioSessionSetProperty(kAudioSessionProperty_AudioCategory, sizeof(sessionCategory), &sessionCategory);
}
AudioSessionSetActive(true);
}
- (void)viewDidUnload {
self.frequencyLabel = nil;
self.playButton = nil;
self.frequencySlider = nil;
AudioSessionSetActive(false);
}

Answer 1

When Core Audio calls your RenderTone callback it wants you to provide a particular number of audio frames per buffer. The 'inNumberFrames' parameter tells you what this number is.
(Core Audio does allow some adjustment of the hardware buffer size but this value may be altered to suit Core Audio e.g. by being rounded up to the next power of 2.)
So you can't adjust the callback buffer size to exactly fit one cycle of a waveform you want to generate: Instead you must keep track of where you currently are in the waveform so you can generate as much or as little of it as required, and then continue where you left off in the next callback.
In your example, if inNumberFrames is 1024 then in the first callback you would supply a complete 960 sample cycle AND an additional 64 samples from the next cycle. In the second callback you would provide the remaining 896 samples of your second cycle and 128 samples from the start of your third cycle, and so on.