WAV File Synthesis From Scratch - C

Question

Recently I saw a video lecture in my CS 101 class that inspired me to start playing with the WAV File Format in C. My project today has been creating sounds using a simple m

Answer 1

I think this is your core problem:

*(sound + (int)(time * samplerate)) = total;

I suspect that (time*samplerate) doesn't always increase on integer boundaries due to floating point rounding errors. Hence, some sample positions are skipped and/or overwritten due to rounding errors. That's just a guess.

But also, as "time" increases, the multiplication of "time * frequency * 2PI" will overflow within a float. So you should normalize "time" such that it doesn't increase forever.

In any case, I validated this modified loop works (and sounds) just fine:

float TWOPI = 6.28318531f;
unsigned int sample_count = length * samplerate;

for (unsigned int i = 0; i < sample_count; i++)
{
    unsigned int j = i % samplerate; // normalize the sample position so that we don't blow up in the subsequent multiplication
    float f = 0.0f;
    int result;

    for (int x = 0; x < 10; x++)
    {
        f += sina[x] * sin((sinf[x] * j * TWOPI) / samplerate);
    }

    result = (long)f;

    //clamp to 16-bit
    if (result > 32767)
    {
        result = 32767;
    }
    else if (result < -32768)
    {
        result = -32768;
    }

    sound[i] = (short)result;

    //printf("%d\n", sound[i]);

}