线性插值-音频音调偏移

Question

我正在试着在一个样本上做音调变换。我使用的是线性插值方法。

如果基准量是一个整数值，则基准值被整齐地移位。如果音调偏移的量是合理的，那么声音就会严重失真。这个实现似乎起作用了。

这是我的代码，我试着注释好。

public void generateOutTrack()
{
    Note currNote;
    float[] output=new float[pattern.getPlayTimeInSmps()];//returns total play time of pattern in #samples.


    float[] currSample=sample.getData();//the pcm data of the sample to be used
    int currPeriod=0;//length of next note in number of samples
    int outputPtr=0;//points to next sample in output buffer array
    float pitch;//amount to pitch sample by
    float linInt=0;//linear interpolater
    float phasePtr=0;//floating point index in sample
    int ptr=0;//integer index into sample

    JavAud.checkRange(currSample);

    while((currNote=pattern.nextNote())!=null)//each iteration plays one note
    {

        currPeriod=currNote.getPeriodInSmps();//length of current note in samples
        pitch=currNote.getPitch();//pitch of current note

        for(int i=0;i<currPeriod;i++)//run for length of note
        {   
            ptr=(int)phasePtr;//floor of floating point index
            linInt=phasePtr-ptr;

            //if we are not at end of sample copy data to output
            if(ptr<currSample.length*(1/pitch)-1)
            {

                //linear interpolation pitch shifting
                output[outputPtr]=(currSample[ptr+1]*linInt)+(currSample[ptr]*(1-linInt));

                //alternate pitch shifting by simple sample dropping(has less distortion)
                //output[outputPtr]=currSample[ptr];

            }
            else//else silent
            {
                output[outputPtr]=0;
            }   

            outputPtr++;
            phasePtr=phasePtr+pitch;
        }

        phasePtr=0;

    }
    JavAud.checkRange(output);
    WavFileWriter writer = new WavFileWriter();
    writer.writeWave(new WavFile(1, JavAud.GLB_SMP_RATE, output), "outputTone.wav");

}

Answer 1

看起来你是想通过重采样来改变音调。要实现比线性插值更好的质量重采样，一种常见的方法是使用加窗正弦低通滤波器作为插值内核。窗口Sinc重采样的一种(慢速)方法的伪代码如下：http://www.nicholson.com/rhn/dsp.html#3