iOS正弦波生成-听得见的咔嗒声 [英] iOS sine wave generation - audible clicking

问题描述

我正在为iOS创建一个合成器。在玩转并尝试学习核心音频之后，我遇到了一个无法解决的问题。我的正弦波会按固定间隔发出咔嗒声，我猜这与相位有关。我看过有关该主题的几本指南和书籍，所有都表明我做得正确。

I am in the process of creating a synthesiser for iOS. After playing around and attempting to learn core audio, I have encountered a problem that I cannot get my head around. My sine wave makes a clicking noise on regular intervals, which Im guessing is related to the phase. I have looked at several guides and books on the subject, and all suggest that I am doing it correctly.

如果有人愿意为我看我的代码

If anybody would be so kind to look at my code for me it would be greatly appreciated.

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;
}

推荐答案

该阶段可能因错误而溢出点

The phase can overflow on wrong point

替换为：

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

with

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

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