#include "mbed.h"
#include "USBAudio.h"
 
// frequency: 8 kHz
#define FREQ 8000
 
// 1 channel: mono
#define NB_CHA 1
 
// length of an audio packet: each ms, we receive 48 * 16bits ->48 * 2 bytes. as there is one channel, the length will be 48 * 2 * 1
#define AUDIO_LENGTH_PACKET (FREQ/500) * NB_CHA
 
// as we don't use audio in, 48000 and 1 are dummy
USBAudio audio(48000, 1, FREQ, NB_CHA, 0x1007, 0xa455);
 
AnalogIn mic(p20);
 
int16_t buf[AUDIO_LENGTH_PACKET/2];
 
int main() {
    double mic_mean = 0.0;
    double mic_value;
 
    // compute average value of the microphone. We can then center the audio signal sent to the computer
    for (int j = 0; j < 1000; j++) {
        mic_value = (mic.read_u16() >> 3);
        mic_mean = (mic_mean*j + mic_value)/(j+1);
    }
 
    while (1) {
        for (int i = 0; i < AUDIO_LENGTH_PACKET/2; i++) {
            buf[i] = (mic.read_u16() >> 3) - mic_mean;
            if (i != AUDIO_LENGTH_PACKET/2) {
                wait_us(80);
            }
        }
        audio.write((uint8_t *)buf);
    }
}

how do I get the audio signal as big as my sound card http://tinypic.com/r/j0z6li/6 bigger audio signal http://tinypic.com/r/r6xxfn/6 <<code>> #include "mbed.h" #include "USBAudio.h" // frequency: 8 kHz #define FREQ 8000 // 1 channel: mono #define NB_CHA 1 // length of an audio packet: each ms, we receive 48 * 16bits ->48 * 2 bytes. as there is one channel, the length will be 48 * 2 * 1 #define AUDIO_LENGTH_PACKET (FREQ/500) * NB_CHA // as we don't use audio in, 48000 and 1 are dummy USBAudio audio(48000, 1, FREQ, NB_CHA, 0x1007, 0xa455); AnalogIn mic(p20); int16_t buf[AUDIO_LENGTH_PACKET/2]; int main() { double mic_mean = 0.0; double mic_value; // compute average value of the microphone. We can then center the audio signal sent to the computer for (int j = 0; j < 1000; j++) { mic_value = (mic.read_u16() >> 3); mic_mean = (mic_mean*j + mic_value)/(j+1); } while (1) { for (int i = 0; i < AUDIO_LENGTH_PACKET/2; i++) { buf[i] = (mic.read_u16() >> 3) - mic_mean; if (i != AUDIO_LENGTH_PACKET/2) { wait_us(80); } } audio.write((uint8_t *)buf); } } <</code>>