iphone core audio data from microphone is NaN - iphone

Question

When I receive data from the microphone via core audio, sometimes the buffers have only one sample inside and sometimes they have 20 samples. some of the time the values of the samples are 0.00000 and sometimes their values are NaN, some of the time, they are what you would expect.
What is the problem?
Here is my code:
-(void)startListeningWithFrequency:(float)frequency;
{
OSStatus status;
//AudioComponentInstance audioUnit;
AudioComponentDescription desc;
desc.componentType = kAudioUnitType_Output;
desc.componentSubType = kAudioUnitSubType_RemoteIO;
desc.componentFlags = 0;
desc.componentFlagsMask = 0;
desc.componentManufacturer = kAudioUnitManufacturer_Apple;
AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);
status = AudioComponentInstanceNew( inputComponent, &audioUnit);
checkStatus(status);
UInt32 flag = 1;
status = AudioUnitSetProperty(audioUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input,kInputBus, &flag, sizeof(flag));
checkStatus(status);
AudioStreamBasicDescription audioFormat;
audioFormat.mSampleRate = 44100.00;//44100.00;
audioFormat.mFormatID = kAudioFormatLinearPCM;
audioFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
audioFormat.mFramesPerPacket = 1;
audioFormat.mChannelsPerFrame = 1;
audioFormat.mBitsPerChannel = 16;
audioFormat.mBytesPerPacket = 2;
audioFormat.mBytesPerFrame = 2;
status = AudioUnitSetProperty(audioUnit,
kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Output,
kInputBus,
&audioFormat,
sizeof(audioFormat));
checkStatus(status);
//status = AudioUnitSetProperty(audioUnit,
// kAudioUnitProperty_StreamFormat,
// kAudioUnitScope_Input,
// kOutputBus,
// &audioFormat,
// sizeof(audioFormat));
checkStatus(status);
AURenderCallbackStruct callbackStruct;
callbackStruct.inputProc = recordingCallback;
callbackStruct.inputProcRefCon = self;
status = AudioUnitSetProperty(audioUnit,
kAudioOutputUnitProperty_SetInputCallback,
kAudioUnitScope_Global,
kInputBus, &callbackStruct, sizeof(callbackStruct));
checkStatus(status);
/* UInt32 shouldAllocateBuffer = 1;
AudioUnitSetProperty(audioUnit, kAudioUnitProperty_ShouldAllocateBuffer, kAudioUnitScope_Global, 1, &shouldAllocateBuffer, sizeof(shouldAllocateBuffer));
*/
//float bufferLength = 0.005;
//AudioSessionSetProperty(kAudioSessionProperty_PreferredHardwareIOBufferDuration, sizeof(bufferLength), &bufferLength);
status = AudioOutputUnitStart(audioUnit);
}
and the callback:
static OSStatus recordingCallback(void *inRefCon,
AudioUnitRenderActionFlags *ioActionFlags,
const AudioTimeStamp *inTimeStamp,
UInt32 inBusNumber,
UInt32 inNumberFrames,
AudioBufferList *ioData) {
AudioBuffer buffer;
buffer.mNumberChannels = 1;
buffer.mDataByteSize = inNumberFrames * 2;
NSLog(#"%d",inNumberFrames);
buffer.mData = malloc( inNumberFrames * 2 );
// Put buffer in a AudioBufferList
AudioBufferList bufferList;
bufferList.mNumberBuffers = 1;
bufferList.mBuffers[0] = buffer;
OSStatus status;
status = AudioUnitRender(audioUnit,
ioActionFlags,
inTimeStamp,
inBusNumber,
inNumberFrames,
&bufferList);
checkStatus(status);
double *q = (double *)(&bufferList)->mBuffers[0].mData;
for(int i=0; i < strlen((const char *)(&bufferList)->mBuffers[0].mData); i++)
{
//i sometimes doesn't get past 0, sometimes goes into 20s
NSLog(#"%f",q[i]);//returns NaN, 0.00, or some times actual data
}
}
Any help would be appreciated,
Thank you,
nonono

Answer 1

Since you are passing the kAudioFormatFlagIsSignedInteger flag for the stream format your samples are just that: 16-bit signed integers (int16_t) and not floats. You either need to treat the samples that way or use the kAudioFormatFlagIsFloat flag instead (and you would need to use float instead of double as datatypes, AFAIK).