tone.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

void GenerateTone(double frequency, double sampleRate, double amplitude, double fadeTime, double *buffer, int length)
{
	double phase;
	double phaseIncrement;
	double *fadeSamples;
	int fadeLength;
	int centerLength;
	int i;
	fadeLength = (int)(fadeTime*sampleRate);
	centerLength = length-(fadeLength*2);
	if (centerLength < 0)
	{
		centerLength = 0;
	}
	if ((fadeLength*2)+centerLength > length)
	{
		return;
	}
	fadeSamples = (double *)malloc(fadeLength*sizeof(double));
	if (!fadeSamples)
	{
		return;
	}
	phaseIncrement = 2*M_PI*0.25/(double)fadeLength;
	phase = 0;
	for (i = 0; i < fadeLength; i++)
	{
		double sample = sin(phase);
		fadeSamples[i] = sample*sample;
		phase += phaseIncrement;
		if (phase >= 2*M_PI)
		{
			phase -= 2*M_PI;
		}
	}
	phaseIncrement = 2*M_PI*frequency/sampleRate;
	phase = 0;
	for (i = 0; i < fadeLength; i++)
	{
		double sample = amplitude*sin(phase);
		phase += phaseIncrement;
		if (phase >= 2*M_PI)
		{
			phase -= 2*M_PI;
		}
		*buffer = fadeSamples[i]*sample;
		buffer++;
	}
	for (i = 0; i < centerLength; i++)
	{
		double sample = amplitude*sin(phase);
		phase += phaseIncrement;
		if (phase >= 2*M_PI)
		{
			phase -= 2*M_PI;
		}
		*buffer = sample;
		buffer++;
	}
	for (i = fadeLength-1; i>= 0; i--)
	{
		double sample = amplitude*sin(phase);
		phase += phaseIncrement;
		if (phase >= 2*M_PI)
		{
			phase -= 2*M_PI;
		}
		*buffer = fadeSamples[i]*sample;
		buffer++;
	}
	free(fadeSamples);
}

int main()
{
	double buffer[44100];
	FILE *out;
	GenerateTone(440, 44100, 1, 0.002, buffer, sizeof(buffer)/sizeof(double));
	out = fopen("output", "wb");
	fwrite(buffer, 1, sizeof(buffer), out);
	fclose(out);
	return 0;
}