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我正在为 iOS 创建一个合成器。在玩耍并尝试学习核心音频之后，我遇到了一个我无法理解的问题。我的正弦波会定期发出咔哒声，我猜这与相位有关。我查看了有关该主题的几本指南和书籍，并且都表明我做得正确。

如果有人愿意为我查看我的代码，将不胜感激。

static OSStatus renderInput(void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData)
{


    // Get a reference to the object that was passed with the callback
    // In this case, the AudioController passed itself so
    // that you can access its data.
    AudioController *THIS = (AudioController*)inRefCon;

    // Get a pointer to the dataBuffer of the AudioBufferList
    AudioSampleType *outA = (AudioSampleType *)ioData->mBuffers[0].mData;

    float freq = THIS->Frequency;   
    float phase = THIS->sinPhase;

    float envValue;
    float sinSignal;

    // The amount the phase changes in  single sample
    double phaseIncrement = 2 * M_PI * freq / kGraphSampleRate;

    // Loop through the callback buffer, generating samples
    for (UInt32 i = 0; i < inNumberFrames; ++i) {       

        sinSignal = sin(phase);

        envValue = THIS->env.tick();

        // Put the sample into the buffer
        // Scale the -1 to 1 values float to
        // -32767 to 32767 and then cast to an integer
        outA[i] = (SInt16)(((sinSignal * 32767.0f) / 2) * envValue);

        phase = phase + phaseIncrement;

        if (phase >= (2 * M_PI * freq)) {
            phase = phase - (2 * M_PI * freq);
        }
    }

    // Store the phase for the next callback.
    THIS->sinPhase = phase;

    return noErr;
}
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3 回答 3

6

相位可能在错误的点溢出

替换这个：

if (phase >= (2 * M_PI * freq)) {
    phase = phase - (2 * M_PI * freq); 
}

和

if (phase >= (2 * M_PI)) { 
    phase = phase - (2 * M_PI); 
}
于 2012-04-03T20:19:01.157 回答
2

如果您的频率不完全是整数值，则此行：

phase = phase - (2 * M_PI * freq);

将以不等于 2pi 的量调整和旋转相位，从而产生不连续性。

于 2012-04-03T21:09:20.413 回答
1

对于这些类型的问题，一个很好的调试技术是在示波器或波形编辑器中查看您的音频。准确查看点击发生的时间和频率通常会提供一些关于点击发生原因的线索。

相同的技术可以用于不是“音频”信号的信号，例如包络发生器等。只要确保你关掉你的扬声器！

于 2012-04-05T05:20:14.717 回答