Experiment with generating sound in wave-format

generatewav.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

struct GlobalFormat {
  unsigned int id;
  unsigned int size;
  unsigned int type;
};

struct FormatChunk {
  unsigned int   dwId;
  unsigned int   dwSize;
  short          wFormatTag;
  unsigned short wChannels;
  unsigned long  dwSamplesPerSec;
  unsigned long  dwAvgBytesPerSec;
  unsigned short wBlockAlign;
  unsigned short wBitsPerSample;
};

int main(int argc, char** argv)
{
	struct FormatChunk fmt;
	fmt.dwId = 0x20746d66; // "fmt "
	fmt.dwSize = 16;
	fmt.wFormatTag = 1; 
	fmt.wChannels = 1;
	fmt.wBitsPerSample = 16;
	fmt.dwSamplesPerSec = 22050;
	fmt.dwAvgBytesPerSec = fmt.dwSamplesPerSec * fmt.wBitsPerSample/8;
	fmt.wBlockAlign = 4;

	if (argc != 5) {
		printf("usage: ./generatewav amplitude frequency length filename\n");
		return 0;
	}

	unsigned short amplitude = (unsigned short)atoi(argv[1]);
	double frequency = (double)atoi(argv[2]);
	int length = atoi(argv[3]) * fmt.dwSamplesPerSec * fmt.wChannels * fmt.wBitsPerSample / 8;
	char* fileName = argv[4];

	FILE* fh = fopen(fileName, "w");

	struct GlobalFormat format;
	format.id = 0x46464952; // RIFF
	format.size = length;
	format.type = 0x45564157; // WAVE
	
	fwrite(&format, sizeof(struct GlobalFormat), 1, fh);

	fwrite(&fmt, sizeof(struct FormatChunk), 1, fh);

	unsigned int dataId = 0x61746164;
	fwrite(&dataId, sizeof(unsigned int), 1, fh);

	unsigned int dataLength = length - 12 - 16 - 12; 
	fwrite(&dataLength, sizeof(unsigned int), 1, fh);

	int i;
	double period = 2*M_PI/((double)fmt.dwSamplesPerSec/frequency);	
	printf("frequency: %f\n", frequency);
	printf("period: %f\n", period);
	printf("amplitude: %d\n", amplitude);
	for (i = 0; i < dataLength; i += 2) {
		if (i > 100) {
			break;
		}
		unsigned short sample = amplitude * (1 + sin(period*(double)i));
		printf("%hd\n", sample);
		fwrite(&sample, sizeof(unsigned short), 1, fh);
	}

	fclose(fh);

	return 0;
}