這是可以成功 Real-time monitor 的程式碼，並且將6個輸入轉換成 mono 輸出

#include <stdio.h>
#include <math.h>
#include <unistd.h>

#include "portaudio.h"

#define FRAME_BLOCK_LEN 256
#define SAMPLING_RATE 44100
#define INPUT_CHANNEL 8  // 6mic + 2 AC108 ADC
#define OUTPUT_CHANNEL 1

PaStream *audioStream;

// Callback Function (DSP Here)
int audio_callback(const void *inputBuffer,
                   void *outputBuffer, 
                   unsigned long framesPerBuffer,
                   const PaStreamCallbackTimeInfo* timeInfo,
                   PaStreamCallbackFlags statusFlags,
                   void *userData){

    float *in = (float*) inputBuffer, *out = (float*)outputBuffer;
    static double phase = 0;
    unsigned long i;
    for( i=0; i < framesPerBuffer; i++ ) {
        float temp=0;
        for(int j=0;j<INPUT_CHANNEL;j++){
            temp+=*in++/6;
        }
        *out++ = temp;
    }
    return paContinue;
}

void init_stuff(){
    int i,id;
    const PaDeviceInfo *info;
    const PaHostApiInfo *hostapi;
    PaStreamParameters outputParameters, inputParameters;

    Pa_Initialize(); // initialize portaudio

    id = Pa_GetDefaultOutputDevice();
    info = Pa_GetDeviceInfo(id);
    hostapi = Pa_GetHostApiInfo(info->hostApi);
    printf("output device [%s] %s\\n",hostapi->name, info->name);
    outputParameters.device = id;
    outputParameters.channelCount = OUTPUT_CHANNEL;
    outputParameters.sampleFormat = paFloat32; // 都用float
    outputParameters.suggestedLatency = 0;
    outputParameters.hostApiSpecificStreamInfo = NULL; // no specific info

    sleep(0.5);
    id = Pa_GetDefaultInputDevice();
    info = Pa_GetDeviceInfo(id);
    hostapi = Pa_GetHostApiInfo(info->hostApi);
    printf("input device [%s] %s\\n",
    hostapi->name, info->name);
    inputParameters.device = id;
    inputParameters.channelCount = INPUT_CHANNEL; // 2 input
    inputParameters.sampleFormat = paFloat32;
    inputParameters.suggestedLatency = 0;
    inputParameters.hostApiSpecificStreamInfo = NULL;

    Pa_OpenStream(
        &audioStream,
        &inputParameters,       // output parameters
        &outputParameters,      // input parameters
        SAMPLING_RATE,          // set sampling rate
        FRAME_BLOCK_LEN,        // set frames per buffer
        paClipOff,              // set no clip
        audio_callback,         // callback function
        NULL );                 // provide no data for the callback
    
    Pa_StartStream(audioStream); // start the callback mechanism
    printf("running. . . press space bar and enter to exit\\n");
    printf("Latency: %f\\n",info->defaultLowInputLatency);
}

void terminate_stuff(){
    Pa_StopStream( audioStream ); // stop the callback mechanism
    Pa_CloseStream( audioStream ); // clear the audio stream object
    Pa_Terminate(); // terminate portaudio
}

int main(){
    init_stuff();
    while(getchar() != ' ') Pa_Sleep(100);
    terminate_stuff();
    return 0;
}

#Compile and run

gcc filena.c -lportaudio -lm