SDL2播放录制的声音时无关的嗡嗡声

Question

我正在使用SDL2从麦克风中捕获音频并播放它们。当播放开始时，除了录制的声音外，耳机还会听到额外的嗡嗡声。为什么会发生这种情况？如何摆脱它？例如，当我们在电话上交谈时，我们只会听到声音，也没有无关的嗡嗡声。有代码：

#include <QCoreApplication>
#include "SDL.h"
#ifdef __MINGW32__
#undef main
#endif

#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480

//Maximum recording time
const int MAX_RECORDING_SECONDS = 5;

//Maximum recording time plus padding
const int RECORDING_BUFFER_SECONDS = MAX_RECORDING_SECONDS + 1;

//Recording data buffer
Uint8* gRecordingBuffer = NULL;

//Size of data buffer
Uint32 gBufferByteSize = 0;

//Position in data buffer
Uint32 gBufferBytePosition = 0;

//Maximum position in data buffer for recording
Uint32 gBufferByteMaxPosition = 0;

void cb_record(void *userdata, Uint8 *stream, int len) {
    //qDebug() << "...Record";
    //Copy audio from stream
    memcpy( &gRecordingBuffer[ gBufferBytePosition ], stream, len );

    //Move along buffer
    gBufferBytePosition += len;
}

void cb_playback(void *userdata, Uint8 *stream, int len) {
    //qDebug() << "...Playback  " << gBufferBytePosition;
    //Copy audio to stream
    memcpy( stream, &gRecordingBuffer[ gBufferBytePosition ], len );

    //Move along buffer
    gBufferBytePosition += len;
}

int main(int argc, char** argv)
{
    QCoreApplication app(argc,argv);

    SDL_Init(SDL_INIT_AUDIO);
    SDL_AudioSpec want, have;
    SDL_AudioSpec want2, have2;

    SDL_zero(want);
    SDL_zero(want2);

    want.freq = 44100;
    want.format = AUDIO_S16SYS;
    want.channels = 1;
    want.samples = 1024;
    want.callback = cb_record;
    SDL_AudioDeviceID recordingDevice = SDL_OpenAudioDevice(SDL_GetAudioDeviceName(0, 1), 1, &want, &have, 0);
    if (recordingDevice == 0) {
        qDebug() << "Cannot open recording device";
        return 1;
    }

    if (have.format != want.format) {
        qDebug() << "We didn't get the wanted format.";
        return 1;
    }

    //Calculate per sample bytes
    int bytesPerSample = want.channels * ( SDL_AUDIO_BITSIZE( want.format ) / 8 );

    //Calculate bytes per second
    int bytesPerSecond = want.freq * bytesPerSample;

    //Calculate buffer size
    gBufferByteSize = RECORDING_BUFFER_SECONDS * bytesPerSecond;

    //Calculate max buffer use
    gBufferByteMaxPosition = MAX_RECORDING_SECONDS * bytesPerSecond;

    //Allocate and initialize byte buffer
    gRecordingBuffer = new Uint8[ gBufferByteSize ];
    memset( gRecordingBuffer, 0, gBufferByteSize );

    // playback

    want2.freq = 44100;
    want2.format = AUDIO_S16SYS;
    want2.channels = 1;
    want2.samples = 1024;
    want2.callback = cb_playback;
    SDL_AudioDeviceID playbackDevice = SDL_OpenAudioDevice(NULL, SDL_FALSE, &want2, &have2, 0);

    if (playbackDevice == 0) {
        qDebug() << "Failed to open audio device: ";
        return 1;
    }

    // start recording
    SDL_PauseAudioDevice(recordingDevice, 0);
    SDL_Delay(3000);
    // stop recording
    SDL_PauseAudioDevice(recordingDevice, 1);

    // reset buffer position
    gBufferBytePosition = 0;

    //start playback
    SDL_PauseAudioDevice(playbackDevice, 0);
    SDL_Delay(3000);
    // stop playback
    SDL_PauseAudioDevice(playbackDevice, 1);
    return app.exec();
}