FFT of samples from portAudio stream - macos

Question

Beginner here, (OSX 10.9.5, Xcode 6)
I have a portAudio stream that gives out noise. Now I'd like to get those random values generated in the callback and run them through an fftw plan. As far as I know, fftw needs to be executed in the main. So how can I show the numbers from the callback to the main? I have a feeling it has something to do with pointers but that's a very uneducated guess...
I'm having some difficulty with joining two different libraries. Little help would be greatly appreciated, thank you!
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include "portaudio.h"
#include "fftw3.h"
#define NUM_SECONDS (1)
#define SAMPLE_RATE (44100)
typedef struct
{
float left_phase;
float right_phase;
}
paTestData;
static int patestCallback( const void *inputBuffer, void *outputBuffer,
unsigned long framesPerBuffer,
const PaStreamCallbackTimeInfo* timeInfo,
PaStreamCallbackFlags statusFlags,
void *userData )
{
/* Cast data passed through stream to our structure. */
paTestData *data = (paTestData*)userData;
float *out = (float*)outputBuffer;
unsigned int i;
(void) inputBuffer; /* Prevent unused variable warning. */
for( i=0; i<framesPerBuffer; i++ )
{
*out++ = data->left_phase; /* left */
*out++ = data->right_phase; /* right */
/* Generate random value that ranges between -1.0 and 1.0. */
data->left_phase = (((float)rand()/(float)(RAND_MAX)) * 2) - 1 ;
data->right_phase = (((float)rand()/(float)(RAND_MAX)) * 2) - 1 ;
printf("%f, %f\n", data->left_phase, data->right_phase);
}
return 0;
}
/*******************************************************************/
static paTestData data;
int main(void);
int main(void)
{
PaStream *stream;
PaError err;
printf("PortAudio Test: output noise.\n");
/* Initialize our data for use by callback. */
data.left_phase = data.right_phase = 0.0;
/* Initialize library before making any other calls. */
err = Pa_Initialize();
if( err != paNoError ) goto error;
/* Open an audio I/O stream. */
err = Pa_OpenDefaultStream( &stream,
0, /* no input channels */
2, /* stereo output */
paFloat32, /* 32 bit floating point output */
SAMPLE_RATE,
512, /* frames per buffer */
patestCallback,
&data );
if( err != paNoError ) goto error;
err = Pa_StartStream( stream );
if( err != paNoError ) goto error;
/* Sleep for several seconds. */
Pa_Sleep(NUM_SECONDS*1000);
err = Pa_StopStream( stream );
if( err != paNoError ) goto error;
err = Pa_CloseStream( stream );
if( err != paNoError ) goto error;
Pa_Terminate();
printf("Test finished.\n");
return err;
error:
Pa_Terminate();
fprintf( stderr, "An error occured while using the portaudio stream\n" );
fprintf( stderr, "Error number: %d\n", err );
fprintf( stderr, "Error message: %s\n", Pa_GetErrorText( err ) );
return err;
}

Answer 1

You could try running the stream in "blocking write" mode instead of using the callback. To use this mode, you pass NULL for the streamCallback parameter of Pa_OpenDefaultStream and then you continually call Pa_WriteStream in a loop. The call will block as necessary. Something like this pseudo code:
Pa_OpenStream(&stream, 0, 2, paFloat32, SAMPLE_RATE, 512, NULL, NULL);
Pa_StartStream(stream);
float interleavedSamples[2*512];
for (int i = 0 ; i < SAMPLE_RATE/512 ; i++) // approx 1 second
{
GenerateNoise(&interleavedSamples, 2, 512, &data);
RunFft(interleavedSamples, ...);
PaWriteStream(stream, interleavedSamples, 512);
}