Question

I have searched almost SO & few forums, but unable to figure out. I have not coded this from scratch. I got the code and I am trying to modify as per my requirement.

So firstly credits to original coder. I am ref this : http://www3.nd.edu/~dthain/courses/cse20211/fall2013/wavfile/

Here he is creating the sine wave for just 1 second. But I am unable to surpass this point. I need to play it for atleast 20seconds.

Here is my code. Hope to get some pointer/help. Thanks in advance. Again thanks to original coder.

WAVFILE_SAMPLES_PER_SECOND = 44100

example.c file

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <errno.h>

#include "wavfile.h"

const int NUM_SAMPLES = (WAVFILE_SAMPLES_PER_SECOND*2);

int main()
{
    unsigned long waveform[NUM_SAMPLES*4]; // here I am changing it to 4
    double frequency = 440;
    int volume = 255;
    unsigned long int length = NUM_SAMPLES*4; // here I am changing it to 4

    // For one second the length = 88200
    unsigned long int i;
    for(i=0;i<length;i++) {
        long double t = (long double) i / WAVFILE_SAMPLES_PER_SECOND;
        waveform[i] = volume*sin(frequency*t*2*M_PI);
    }

    printf("length=%d\n",length);
    FILE * f = wavfile_open("sound.wav");
    if(!f) {
        printf("couldn't open sound.wav for writing: %s",strerror(errno));
        return 1;
    }

    wavfile_write(f,waveform,length);
    wavfile_close(f);

    return 0;
}

wave.h file

#ifndef WAVFILE_H
#define WAVFILE_H

#include <stdio.h>
#include <inttypes.h>

FILE * wavfile_open( const char *filename );
void wavfile_write( FILE *file, short data[], int length );
void wavfile_close( FILE * file );

#define WAVFILE_SAMPLES_PER_SECOND 44100

#endif

The file is created successfully. But I am unable to play it in any player. Can any one help. Thanks again

Answer 1

With the original code, to get 20 seconds you just need to change the line

const int NUM_SAMPLES = (WAVFILE_SAMPLES_PER_SECOND*2);

to

const int NUM_SAMPLES = (WAVFILE_SAMPLES_PER_SECOND*20);

Answer 2

In the original version a wav file of 1 second was created. As I understand that was working fine. The following line writes 1 second of audio tho the .wav file:

wavfile_write(f,waveform,length);

It should be possible to call that line 20 times in a loop, to get 20 seconds of audio. As the frequency of the sine is 440 Hz, 440 full sines fit into a second. So the sine is at the same position at the start of the 2nd second as it was at the 1st. So I think the sine should be correct.

issue when generating sine wave for more than 1 second

2 个答案: