アクティブバンドパスフィルタ２

　パッシブバンドフィルタが上手くいかなかったのでオペアンプを使用してアクティブバンドフィルタの実験を行いました。

R1=4649Ω
R2=4763Ω
R3=477.8kΩ
C1=287pF
C2=295pF
IC=UPC741C
Q=7.125
f0=16314.28Hz

　可聴周波数をスイープして出力しフィルタを通した様子です。フィルタが機能しているのが判ります。しかし、複数の信号を狭い帯域に載せるにはもっとQが高くないと分離が上手くいかないような気がします。

#include <iostream>
#include <windows.h>
#include <math.h>
#include <MMSystem.h>

#pragma comment (lib, "winmm.lib")

void createWave(LPWORD lpData, size_t frequency, size_t sampling, WORD amplitude) {
    size_t wavelength = sampling / frequency;
    double d = 360.0 / wavelength;
    double pi = 3.14159265359;
    for (int i = 0; i < wavelength; i++) {
        lpData[i] = (WORD)(amplitude * sin(d * (i % wavelength) / 180.0 * pi));
    }
}

int main() {

    WAVEFORMATEX wfe;
    static HWAVEOUT hWaveOut;
    static WAVEHDR whdr;
    static LPWORD lpWave;
    static LPWORD lpData;

    // 最初と最後の1sは出力しないので3以上とする
    size_t terms = 7;

    size_t i, j, start, end;
    size_t frequency = 400;
    size_t sampling = 384000;
    size_t wavelength = sampling / frequency;

    wavelength = sampling / frequency;
    wfe.wFormatTag = WAVE_FORMAT_PCM;
    wfe.nChannels = 2;
    wfe.wBitsPerSample = 16;
    wfe.nBlockAlign = wfe.nChannels * wfe.wBitsPerSample / 8;
    wfe.nSamplesPerSec = (DWORD)sampling;
    wfe.nAvgBytesPerSec = wfe.nSamplesPerSec * wfe.nBlockAlign;
    waveOutOpen(&hWaveOut, 0, &wfe, 0, 0, CALLBACK_NULL);
    lpWave = (LPWORD)calloc(sizeof(WORD), wfe.nChannels * sampling * terms);

    end = sampling * wfe.nChannels * 1;
    WORD amplitude = 32767;
    for (i = 0; i < end; i++) {
        lpWave[i] = 0;
    }

    // 最初の1sは出力しない
    start = sampling * wfe.nChannels * 1;
    end = wfe.nChannels * sampling * terms;
    // 最後の1sは出力しない
    end -= sampling * wfe.nChannels * 1;

    size_t valWavelength;
    size_t valFrequency;
    for (i = start, j = 0; i < end; i += 2) {
        if (j == 0) {
            valFrequency = frequency + ((i - start) * (20000.0- frequency)) / (sampling * wfe.nChannels * (terms - 2));
            valWavelength = sampling / valFrequency;
            lpData = (LPWORD)calloc(sizeof(WORD), valWavelength);
            createWave(lpData, valFrequency, sampling, amplitude);
        }
        lpWave[i] = lpData[j];
        ++j;
        if (j >= valWavelength) {
            j = 0;
            free(lpData);
        }
    }

    lpData = (LPWORD)calloc(sizeof(WORD), wavelength);
    createWave(lpData, frequency, sampling, amplitude);
    for (i = start+1, j = 0; i < end; i += 2) {
        lpWave[i] = lpData[j];
        ++j;
        if (j >= wavelength) { j = 0; }
    }
    free(lpData);

    whdr.lpData = (LPSTR)lpWave;
    whdr.dwBufferLength = wfe.nAvgBytesPerSec * terms;
    whdr.dwFlags = WHDR_BEGINLOOP | WHDR_ENDLOOP;
    whdr.dwLoops = 1;
    waveOutPrepareHeader(hWaveOut, &whdr, sizeof(WAVEHDR));
    waveOutWrite(hWaveOut, &whdr, sizeof(WAVEHDR));
    
    char str[128];
    std::cout << "hello, world\n";
    std::cin >> str;

}