在iPhone上为fft设置加速器框架

问题描述:

在阅读完以下内容后,我已经设置了用于设置加速器的功能:

I have set a function to setup the accelerator, after i have read :

使用Apple FFT和加速框架

具有加速框架vDSP的iPhone FFT

和Apple文档。

我这样做了:

void fftSetup()
{

    COMPLEX_SPLIT   A;
    FFTSetup        setupReal;
    uint32_t        log2n;
    uint32_t        n, nOver2;
    int32_t         stride;
    uint32_t        i;
    float          *originalReal, *obtainedReal;
    float           scale;
    uint32_t L = 1024;
    float *mag = new float[L/2];


     log2n = 10 ;
     n = 1 << log2n;
     stride = 1;
     nOver2 = n / 2;

    printf("1D real FFT of length log2 ( %d ) = %d\n\n", n, log2n);

    for (i = 0; i < n; i++)
        originalReal[i] = (float) (i + 1);


    vDSP_ctoz((COMPLEX *) originalReal,2,&A,1,nOver2);

    A.realp = (float *) malloc(nOver2 * sizeof(float));
    A.imagp = (float *) malloc(nOver2 * sizeof(float));

    setupReal = vDSP_create_fftsetup(log2n, FFT_RADIX2);

    vDSP_fft_zrip(setupReal, &A, stride, log2n, FFT_FORWARD);
    vDSP_fft_zrip(setupReal, &A, stride, log2n, FFT_INVERSE);




    //get magnitude;
    for(i = 1; i < L/2; i++){
        mag[i] = sqrtf(A.realp[i]*A.realp[i] + A.imagp[i] * A.imagp[i]);
    }





    scale = (float) 1.0 / (2 * n);
    vDSP_vsmul(A.realp, 1, &scale, A.realp, 1, nOver2);
    vDSP_vsmul(A.imagp, 1, &scale, A.imagp, 1, nOver2);


}

问题:


  1. 我的应用始终在这2行之一上崩溃且没有错误(错误访问):




originalReal [i] =(float)(i +1); //或

originalReal[i] = (float) (i + 1); // or

vDSP_ctoz((COMPLEX *)originalReal,2,& A,1,nOver2);

vDSP_ctoz((COMPLEX *) originalReal,2,&A,1,nOver2);

我想我没有为log2n设置一个好的值? (10到1024个窗口?)

i guess i did not set a good value for log2n ? (10 to get 1024 window ? )


  • 我如何获得垃圾箱的真实大小?我实际的英尺?我在这里写的一样吗?

  • how do i get the real magnitude of the bins? my actual fft? the same i wrote here ?

我在哪里输入我的数据缓冲区数组(恰好在我的代码中的什么位置?而不是originalReal?)

where do i input MY data buffer array (exactly where in my code ? instead originalReal?)

非常感谢。

I

这是代码:

   COMPLEX_SPLIT   A;
    FFTSetup        setupReal;
    uint32_t        log2n;
    uint32_t        n, nOver2;
    int32_t         stride;
    uint32_t        i;
    float          *originalReal, *obtainedReal;
    float           scale;
    uint32_t L = 1024;
    float *mag = new float[L/2];


     log2n = 10 ;
     n = 1 << log2n;
     stride = 1;
     nOver2 = n / 2;

    //printf("1D real FFT of length log2 ( %d ) = %d\n\n", n, log2n);

    A.realp = (float *) malloc(nOver2 * sizeof(float));
    A.imagp = (float *) malloc(nOver2 * sizeof(float));
    originalReal = (float *) malloc(n * sizeof(float));
    obtainedReal = (float *) malloc(n * sizeof(float));

     for (i = 0; i < n; i++)
         originalReal[i] = cos(2*3.141592*11000*i/44100);//(float) (i + 1);


    vDSP_ctoz((COMPLEX *) originalReal,2,&A,1,nOver2);



    setupReal = vDSP_create_fftsetup(log2n, FFT_RADIX2);

    vDSP_fft_zrip(setupReal, &A, stride, log2n, FFT_FORWARD);
    //vDSP_fft_zrip(setupReal, &A, stride, log2n, FFT_INVERSE);

    scale = (float) 1.0 / (2 * n);
    vDSP_vsmul(A.realp, 1, &scale, A.realp, 1, nOver2);
    vDSP_vsmul(A.imagp, 1, &scale, A.imagp, 1, nOver2);


    //get magnitude;
    for(i = 1; i < L/2; i++)
    {
        mag[i] = sqrtf(A.realp[i]*A.realp[i] + A.imagp[i] * A.imagp[i]);
           NSLog(@"%d:%f",i,mag[i]);
    }

实际上,这不是垃圾箱之间的44hz,就像那家伙在上面的帖子中写道!但是43! 22050/512 = 43。这个东西很关键!因为在较高的bin中(例如bin [300]),您将获得与44和43完全不同的reault! (其300hz漂移)。因此,请注意。

Actually its not 44hz between bins,as the guy wrote in the post above! but 43 ! 22050/512=43 . this thing is critical ! because in the higher bins- such as bin[300] you get a completely different resault for 44 and 43 ! (its 300hz drift). so take care of that .