如何实时处理来自Kissfft的数据流

Question

我正在尝试使用SDL捕获音频流，然后将其传递给kissfft以确定哪个频率是信号中最主要的频率。但是，无论传入音频是什么信号，我总是得到3986作为最主要正弦波在fft中的位置。我知道我实际上收到了音频信号，因为更改信号时可以看到音量变化（我正在使用键盘生成音频信号）

#include "SDL.h"
#include "kiss_fftr.h"
#include <stdlib.h>

#define NUM_SAMPLES 4096
#define INPUT_DEVICE "Built-in Audio Analog Stereo"

volatile kiss_fftr_cfg kiss_cfg;

volatile int audio_count=0;

//This is what takes each audio sample and process it as an FFT
void AudioCallback(void* userdata, uint8_t *stream, int len1){
    int audioVal =0;
    kiss_fft_scalar in[NUM_SAMPLES];
    int maxSamp =0, minSamp =0;
    for(int i=0; i<len1; i++){`enter code here`
        int val = (int8_t)stream[i];
        maxSamp = (maxSamp < val) ? val :maxSamp;
        minSamp = (minSamp < val)? minSamp : val;
        int thisVal = stream[i] -128;
        if(thisVal < 0)
            thisVal = -1 * thisVal;

        audioVal += thisVal;
        in[i] = thisVal;
    }

    kiss_fft_cpx out[NUM_SAMPLES];
    kiss_fftr(kiss_cfg, in, out);
    long long int max = 0;
    int maxPos = -1;
    for(int i=0; i<NUM_SAMPLES; i++){
        unsigned int thisVal = abs(out[i].r);
        if(max <= thisVal){
            maxPos = i;
            max=thisVal;
        }

    }

    printf("Max pos %7d, max val %15d audioval %15d| samples %d, %d %d %d\n", maxPos, max, audioVal, len1, NUM_SAMPLES, maxSamp, minSamp);

    audio_count++;
}

//In here I both set up kissfft and SDL
int main(int argc, char* argv[]){
    SDL_Init(SDL_INIT_AUDIO);
    int i, count = SDL_GetNumAudioDevices(0);
    printf("Found %d audio devices \n", count);
    if(0 > count){
        printf("Got this error %s\n", SDL_GetError());
    }
    for (i = 0; i < count; ++i) {
        printf("Audio device %d: %s\n", i, SDL_GetAudioDeviceName(i, 0));
    }

    kiss_cfg = kiss_fftr_alloc(NUM_SAMPLES, 0, NULL, NULL);

    SDL_AudioSpec want, have;
    SDL_memset(&want, 0, sizeof(want)); /* or SDL_zero(want) */
    want.freq = 48000;
    want.format = AUDIO_U8;
    want.channels = 1;
    want.samples = NUM_SAMPLES;
    want.callback = AudioCallback;

    SDL_AudioDeviceID devId = SDL_OpenAudioDevice(INPUT_DEVICE, 1, &want, &have, SDL_AUDIO_ALLOW_FORMAT_CHANGE);


    if(0 == devId)
    {
         printf("Failed to open %s\n", INPUT_DEVICE);
         exit(1);
    }

    //SDL_LockAudioDevice(devId);
    SDL_PauseAudioDevice(devId, 0);

    while(1){
        SDL_Delay(10);
    }

    SDL_UnlockAudioDevice(devId);
    SDL_CloseAudioDevice(devId);

}

我希望maxpos会随着我在键盘上按的键的变化而变化，但是我总是得到“ Max pos 3986”。