PortAudio：声音开始和结束时有短噪音

Question

我有类似钢琴的应用程序，当我按下钢琴键时，它会发出声音。在我的应用程序中，我编写了自己的正弦波发生器。应用程序是用 Qt 编写的。我认为问题出在 portAudio 上，但我找不到任何解决方案。

我已经为您录制了我的问题听起来如何：https://vocaroo.com/i/s1yiWjaJffTU

这是我的生成器类：

声音引擎.h

#ifndef SOUNDENGINE_H
#define SOUNDENGINE_H

#include <QThread>
#include <math.h>
#include "portaudio.h"

#define SAMPLE_RATE   (44100)
#define FRAMES_PER_BUFFER  (64)
#define FREQUENCY 220

#ifndef M_PI
#define M_PI  (3.14159265)
#endif

#define TABLE_SIZE   (200)

typedef struct
{
    float sine[TABLE_SIZE];
    int phase;
}
paTestData;

class SoundEngine : public QThread
{
    Q_OBJECT
public:
    bool turnOFF;
    void run();
    static int patestCallback( const void *inputBuffer, void *outputBuffer,unsigned long framesPerBuffer,const PaStreamCallbackTimeInfo* timeInfo,PaStreamCallbackFlags statusFlags,void *userData );
    void generateSine();
    void removeSine();
private:
    paTestData data;
    PaStream *stream;
    PaError err;
    bool isPressed;
};

#endif // SOUNDENGINE_H

声音引擎.cpp

#include "soundengine.h"
#include <QDebug>

void SoundEngine::run()
{
    PaStreamParameters outputParameters;
    int i;
    double t;
    turnOFF = false;
    isPressed = false;

    static unsigned long n=0;
    for( i=0; i<TABLE_SIZE; i++, n++ )
    {
        t = (double)i/(double)SAMPLE_RATE;
        data.sine[i] = 0;
        //data.sine[i] = 0.3*sin(2 * M_PI * FREQUENCY * t);
        /*data.sine[i] *= 1.0/2;
        data.sine[i] += 0.5*sin(2 * M_PI * (FREQUENCY+110) * t);
        data.sine[i] *= 2.0/3;
        data.sine[i] += (1.0/3)*sin(2 * M_PI * (FREQUENCY+60) * t);
        data.sine[i] *= 3.0/4;
        data.sine[i] += (1.0/4)*sin(2 * M_PI * (FREQUENCY+160) * t);*/
    }
    data.phase = 0;

    err = Pa_Initialize();
    if(err != paNoError) qDebug()<<"Błąd przy inicjalizacji strumienia:"<<Pa_GetErrorText(err);

    outputParameters.device = Pa_GetDefaultOutputDevice(); /* default output device */
    if (outputParameters.device == paNoDevice) qDebug()<<"Błąd: Brak domyślnego urządzenia wyjścia!";

    outputParameters.channelCount = 2;       /* stereo output */
    outputParameters.sampleFormat = paFloat32; /* 32 bit floating point output */
    outputParameters.suggestedLatency = Pa_GetDeviceInfo( outputParameters.device )->defaultLowOutputLatency;
    outputParameters.hostApiSpecificStreamInfo = NULL;

    err = Pa_OpenStream(
              &stream,
              NULL, /* no input */
              &outputParameters,
              SAMPLE_RATE,
              FRAMES_PER_BUFFER,
              paClipOff,      /*paNoFlag we won't output out of range samples so don't bother clipping them */
              patestCallback,
              &data );
    if(err != paNoError) qDebug()<<"Błąd przy otwieraniu strumienia:"<<Pa_GetErrorText(err);
    //err = Pa_StartStream( stream );
    if(err != paNoError) qDebug()<<"Błąd przy starcie strumienia:"<<Pa_GetErrorText(err);

    while (turnOFF == false) {
        Pa_Sleep(500);
    }

    //err = Pa_StopStream( stream );
    if(err != paNoError) qDebug()<<"Błąd przy zatrzymywaniu strumienia:"<<Pa_GetErrorText(err);
    err = Pa_CloseStream( stream );
    if(err != paNoError) qDebug()<<"Błąd przy zamykaniu strumienia:"<<Pa_GetErrorText(err);
    Pa_Terminate();
}

int SoundEngine::patestCallback(const void *inputBuffer, void *outputBuffer, unsigned long framesPerBuffer, const PaStreamCallbackTimeInfo *timeInfo, PaStreamCallbackFlags statusFlags, void *userData)
{
    paTestData *callData = (paTestData*)userData;
    float *out = (float*)outputBuffer;
    float sample;
    unsigned long i;

    (void) timeInfo; /* Prevent unused variable warnings. */
    (void) statusFlags;
    (void) inputBuffer;

    for( i=0; i<framesPerBuffer; i++ )
    {
        sample = callData->sine[callData->phase++];
        *out++ = sample;  /* left */
        *out++ = sample;  /* right */
        if( callData->phase >= TABLE_SIZE ) callData->phase -= TABLE_SIZE;
    }

    return paContinue;
}

void SoundEngine::generateSine()
{
    if(isPressed == false)
    {
        for(int i=0; i<TABLE_SIZE; i++)
        {
            data.sine[i] += 0.3*sin(2 * M_PI * 440 * ((double)i/(double)SAMPLE_RATE));
        }
        isPressed = true;
        err = Pa_StartStream( stream );
    }
}

void SoundEngine::removeSine()
{
    err = Pa_StopStream( stream );
    for(int i=0; i<TABLE_SIZE; i++)
    {
        data.sine[i] -= 0.3*sin(2 * M_PI * 440 * ((double)i/(double)SAMPLE_RATE));
    }
    isPressed = false;

}

当我按下按钮时，功能

void SoundEngine::generateSine()

正在运行 - 它会发出声音。当我松开按钮时，方法

void SoundEngine::removeSine()

消除声音。

Answer 1

您的声音或 PortAudio 都没有问题。您最后听到的声音只是音频突然停止的结果。看一下下面的声音图像，该声音在整个持续时间内具有恒定的幅度。此声音最后会发出一声爆裂声。

相反，如果我们通过修改波形的包络（与图像 #1 中的声音相同）来衰减幅度，使其类似于图像 #2 中的声音，我们将不会听到声音中的任何突然变化结束。

总之，如果您的目标是完全消除您听到的爆音，请淡出（或淡入）您的声音。