我怎样才能用 C 语言发出警笛声？

Question

我想发出频率每 0.65 秒变化 960Hz 和 770Hz 的警笛声。（在 8 秒 Wav 文件中）但是我不知道如何构建我上面写的函数。我试着每个时期都用'for(...=0; ... < 0.65; ...++)'。但是 y[0] 和 y[1] 是函数，所以我很困惑。我的最终目标是发出警笛声，从右边传到左边。

言归正传，我想知道如何让频率每0.65秒变960Hz和770Hz。如果您给我建议以实现我的最终目标，我将不胜感激。

由于我的英语不好，如果你很难理解我的问题，请评论我。

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <iostream> 

#pragma once 
#define WAVE_FORMAT_UNKNOWN 0X0000; 
#define WAVE_FORMAT_PCM 0X0001;
#define WAVE_FORMAT_MS_ADPCM 0X0002; 
#define WAVE_FORMAT_IEEE_FLOAT 0X0003; 
#define WAVE_FORMAT_ALAW 0X0006; 
#define WAVE_FORMAT_MULAW 0X0007; 
#define WAVE_FORMAT_IMA_ADPCM 0X0011; 
#define WAVE_FORMAT_YAMAHA_ADPCM 0X0016;
#define WAVE_FORMAT_GSM 0X0031; 
#define WAVE_FORMAT_ITU_ADPCM 0X0040; 
#define WAVE_FORMAT_MPEG 0X0050;
#define WAVE_FORMAT_EXTENSIBLE 0XFFFE;


#define DURATION 8 
#define SAMPLE_RATE 48000
#define CHANNEL 2
#define BIT_RATE 16

typedef struct {
    unsigned char ChunkID[4]; // Contains the letters "RIFF" in ASCII form 
    unsigned int ChunkSize; // This is the size of the rest of the chunk following this number 
    unsigned char Format[4]; // Contains the letters "WAVE" in ASCII form 
} RIFF;

typedef struct {
    unsigned char ChunkID[4]; // Contains the letters "fmt " in ASCII form 
    unsigned int ChunkSize; // 16 for PCM. This is the size of the rest of the Subchunk which follows this number. 
    unsigned short AudioFormat; // PCM = 1 
    unsigned short NumChannels; // Mono = 1, Stereo = 2, etc. 
    unsigned int SampleRate; // 8000, 44100, etc. 
    unsigned int AvgByteRate; // SampleRate * NumChannels * BitsPerSample/8 
    unsigned short BlockAlign; // NumChannels * BitsPerSample/8 
    unsigned short BitPerSample; // 8 bits = 8, 16 bits = 16, etc 
} FMT;

typedef struct {
    char ChunkID[4]; // Contains the letters "data" in ASCII form 
    unsigned int ChunkSize; // NumSamples * NumChannels * BitsPerSample/8 
} DATA;

typedef struct {
    RIFF Riff;
    FMT Fmt;
    DATA Data;
} WAVE_HEADER;



int main() {
    FILE* f_out;
    f_out = fopen("D:\test.wav", "wb");

    WAVE_HEADER header;
    memcpy(header.Riff.ChunkID, "RIFF", 4);
    header.Riff.ChunkSize = DURATION * SAMPLE_RATE * CHANNEL * BIT_RATE / 8 + 36;
    memcpy(header.Riff.Format, "WAVE", 4);

    memcpy(header.Fmt.ChunkID, "fmt ", 4);
    header.Fmt.ChunkSize = 0x10;
    header.Fmt.AudioFormat = WAVE_FORMAT_PCM;
    header.Fmt.NumChannels = CHANNEL;
    header.Fmt.SampleRate = SAMPLE_RATE;
    header.Fmt.AvgByteRate = SAMPLE_RATE * CHANNEL * BIT_RATE / 8;
    header.Fmt.BlockAlign = CHANNEL * BIT_RATE / 8;
    header.Fmt.BitPerSample = BIT_RATE;

    memcpy(header.Data.ChunkID, "data", 4);
    header.Data.ChunkSize = DURATION * SAMPLE_RATE * CHANNEL * BIT_RATE / 8;

    fwrite(&header, sizeof(header), 1, f_out);

    short y[2]; 
    double high_freq = 960;
    double low_freq = 770;
    for (int i = 0; i < SAMPLE_RATE * DURATION; i++) {
        double level_l = (double)i / (SAMPLE_RATE * DURATION);
        double level_r = 1.0 - level_l;

        y[0] = (short)(30000 * sin(2 * 3.141592 * i * high_freq / SAMPLE_RATE) * level_l);
        y[1] = (short)(30000 * sin(2 * 3.141592 * i * low_freq / SAMPLE_RATE) * level_r);
        fwrite(&y[0], sizeof(short), 1, f_out);
        fwrite(&y[1], sizeof(short), 1, f_out);
    }


    fclose(f_out);
    return 0;
}

Answer 1

您正在交替样本上输出两个频率中的每一个。即左声道一个频率的稳音，右声道另一个频率的稳音。

我们需要做的是保持给定子持续时间的相同频率并在它们之间翻转。并且，相同频率被馈送到两个频道[尽管音量级别不同]。

这里有一个轻微的重构可以做到这一点。有注释。

我不确定您使用的级别（例如 level_l 和 level_r）。我认为它们相同听起来更好（即警笛声更近），所以我将 level_r 设为 level_l 作为一个选项。但是，我保留了原始的 L/R 缩放比例。

编辑： 听完上面的内容后，当我缩短子持续时间时，警报器听起来更像是真正的[欧洲]警报器。我不确定它仍然是 0.65 秒，但听起来更好[对我]

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
//#include <iostream>
#include <string.h>
#include <math.h>

//#pragma once
#define WAVE_FORMAT_UNKNOWN 0X0000;
#define WAVE_FORMAT_PCM 0X0001;
#define WAVE_FORMAT_MS_ADPCM 0X0002;
#define WAVE_FORMAT_IEEE_FLOAT 0X0003;
#define WAVE_FORMAT_ALAW 0X0006;
#define WAVE_FORMAT_MULAW 0X0007;
#define WAVE_FORMAT_IMA_ADPCM 0X0011;
#define WAVE_FORMAT_YAMAHA_ADPCM 0X0016;
#define WAVE_FORMAT_GSM 0X0031;
#define WAVE_FORMAT_ITU_ADPCM 0X0040;
#define WAVE_FORMAT_MPEG 0X0050;
#define WAVE_FORMAT_EXTENSIBLE 0XFFFE;

#define DURATION 8
#define SAMPLE_RATE 48000
#define CHANNEL 2
#define BIT_RATE 16

typedef struct {
    unsigned char ChunkID[4];           // Contains the letters "RIFF" in ASCII form
    unsigned int ChunkSize;             // This is the size of the rest of the chunk following this number
    unsigned char Format[4];            // Contains the letters "WAVE" in ASCII form
} RIFF;

typedef struct {
    unsigned char ChunkID[4];           // Contains the letters "fmt " in ASCII form
    unsigned int ChunkSize;             // 16 for PCM. This is the size of the rest of the Subchunk which follows this number.
    unsigned short AudioFormat;         // PCM = 1
    unsigned short NumChannels;         // Mono = 1, Stereo = 2, etc.
    unsigned int SampleRate;            // 8000, 44100, etc.
    unsigned int AvgByteRate;           // SampleRate * NumChannels * BitsPerSample/8
    unsigned short BlockAlign;          // NumChannels * BitsPerSample/8
    unsigned short BitPerSample;        // 8 bits = 8, 16 bits = 16, etc
} FMT;

typedef struct {
    char ChunkID[4];                    // Contains the letters "data" in ASCII form
    unsigned int ChunkSize;             // NumSamples * NumChannels * BitsPerSample/8
} DATA;

typedef struct {
    RIFF Riff;
    FMT Fmt;
    DATA Data;
} WAVE_HEADER;

int
main()
{
    FILE *f_out;

#if 0
    f_out = fopen("D:\test.wav", "wb");
#else
    f_out = fopen("test.wav", "wb");
#endif

    WAVE_HEADER header;

    memcpy(header.Riff.ChunkID, "RIFF", 4);
    header.Riff.ChunkSize = DURATION * SAMPLE_RATE * CHANNEL * BIT_RATE / 8 + 36;
    memcpy(header.Riff.Format, "WAVE", 4);

    memcpy(header.Fmt.ChunkID, "fmt ", 4);
    header.Fmt.ChunkSize = 0x10;
    header.Fmt.AudioFormat = WAVE_FORMAT_PCM;
    header.Fmt.NumChannels = CHANNEL;
    header.Fmt.SampleRate = SAMPLE_RATE;
    header.Fmt.AvgByteRate = SAMPLE_RATE * CHANNEL * BIT_RATE / 8;
    header.Fmt.BlockAlign = CHANNEL * BIT_RATE / 8;
    header.Fmt.BitPerSample = BIT_RATE;

    memcpy(header.Data.ChunkID, "data", 4);
    header.Data.ChunkSize = DURATION * SAMPLE_RATE * CHANNEL * BIT_RATE / 8;

    fwrite(&header, sizeof(header), 1, f_out);

    short y[2];
    double high_freq = 960;
    double low_freq = 770;

#if 0
    for (int i = 0; i < SAMPLE_RATE * DURATION; i++) {
        double level_l = (double) i / (SAMPLE_RATE * DURATION);
        double level_r = 1.0 - level_l;

        y[0] = (short) (30000 * sin(2 * 3.141592 * i * high_freq / SAMPLE_RATE) * level_l);
        y[1] = (short) (30000 * sin(2 * 3.141592 * i * low_freq / SAMPLE_RATE) * level_r);
        fwrite(&y[0], sizeof(short), 1, f_out);
        fwrite(&y[1], sizeof(short), 1, f_out);
    }
#endif

#if 1
    // number of samples to flip on
#if 0
    int flipfreq = (SAMPLE_RATE * 65) / 100;
#else
    int flipfreq = (SAMPLE_RATE * 65) / 200;
#endif

    // current frequency to use
    int curtyp = 0;

    for (int i = 0; i < SAMPLE_RATE * DURATION; i++) {
        // after 0.65 seconds, change the frequency
        if ((i % flipfreq) == 0)
            curtyp = ! curtyp;

        // use the frequency for this period
        double cur_freq = curtyp ? high_freq : low_freq;

        double level_l = (double) i / (SAMPLE_RATE * DURATION);
#if 1
        double level_r = 1.0 - level_l;
#else
        double level_r = level_l;
#endif

        y[0] = (short) (30000 * sin(2 * 3.141592 * i * cur_freq / SAMPLE_RATE) * level_l);
        y[1] = (short) (30000 * sin(2 * 3.141592 * i * cur_freq / SAMPLE_RATE) * level_r);
        fwrite(&y[0], sizeof(short), 1, f_out);
        fwrite(&y[1], sizeof(short), 1, f_out);
    }
#endif

    fclose(f_out);
    return 0;
}

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