Why my window function isn't removing harmonics? - c++

Question

I have been working on creating a mixed wave signal. My code is in c++ :
Server signal:
void server_sineWave(BitDepth buffer[], double sin_freq, double beep_freq) {
BitDepth amplitude = std::numeric_limits<BitDepth>::max() * 0.5;
QWORD c = 0;
double d = (samplerate / sin_freq);
int initial = NUM_SAMPLES / 25;
for (QWORD i = 0; i < NUM_SAMPLES; i += channels) {
buffer[i] = amplitude * sin((2 * pi * sin_freq * i) / samplerate); // sin wave generated at "freq"
if (i == initial) {
for (QWORD j = 0; j < 480; j++) {
double stream = amplitude * sin((2 * pi * sin_freq * i / samplerate));
double beep = amplitude * sin((2 * pi * beep_freq * j / samplerate));
double multiplier = .4 * (1 - cos(2 * pi * j / 480));
buffer[i] = stream + (beep * multiplier);
i++;
}
initial = i + 19200.0;
}
}
}
Client signal:
void client_sineWave(BitDepth buffer[], double sin_freq, double beep_freq) {
BitDepth amplitude = std::numeric_limits<BitDepth>::max() * 0.5;
QWORD c = 0;
double d = (samplerate / sin_freq);
int initial = NUM_SAMPLES / 25;
for (QWORD i = 0; i < NUM_SAMPLES; i += channels) {
buffer[i] = amplitude * sin(2 * pi * sin_freq * i / samplerate); // sin wave generated at "freq"
if (i == initial) {
for (QWORD j = 0; j < 480; j++) {
double stream = amplitude * sin((2 * pi * sin_freq * i / samplerate));
double beep = amplitude * sin((2 * pi * beep_freq * j / samplerate));
double multiplier = .4 * (1 - cos(2 * pi * j / 480));
buffer[i] = stream + (beep * multiplier);
// buffer[i] += (beep * multiplier);
i++;
}
initial = i + 19200.0;
//(1000 + rand() % 10000)
//double deg = 360.0 / d;
//buffer[i] = buffer[i + (1 * (channels - 1))] = sin((c++ * deg) * pi / 180) * amplitude;
}
}
}
Mixing of server and client signals:
void mix(BitDepth buffer[], BitDepth server[], BitDepth client[], double duration_milliseconds) {
QWORD num_samples = duration_milliseconds * (NUM_SAMPLES / 10000.0);
double tmp = 0;
QWORD size = NUM_SAMPLES + num_samples;
BitDepth *server_delay = new BitDepth[size];
BitDepth *client_delay = new BitDepth[size];
for (QWORD i = 0; i < size; i++) {
if (i < num_samples) {
server_delay[i] = 0;
client_delay[i + NUM_SAMPLES] = 0;
}
if (i > num_samples) {
server_delay[i] = server[i - num_samples];
client_delay[i - num_samples] = client[i - num_samples];
}
}
for (QWORD i = 0; i < NUM_SAMPLES; i += channels) {
// double multiplier = .5 * (1 - cos(2 * pi * i / NUM_SAMPLES-1));
// double multiplier = (0.54 - 0.46 * cos(2.0 * M_PI * (double) i / (double) (NUM_SAMPLES - 1)));
// server_delay[i] = multiplier * (server_delay[i]);
// client_delay[i] = multiplier * (client_delay[i]);
tmp = server_delay[i] + client_delay[i];
if (tmp > 32767) {
tmp = 32767;
} else if (tmp < -32768) {
tmp = -32768;
}
buffer[i] = tmp;
}
}
My Result in spectrogram from the above code:
Now, when I change the amplitude by increasing value from 0.5 to 0.8, in the following line:
BitDepth amplitude = std::numeric_limits<BitDepth>::max() * 0.5;
to
BitDepth amplitude = std::numeric_limits<BitDepth>::max() * 0.8;
I get following result:
I am new in DSP c++ programming and I really don't know what is this issue and how to resolve this issue?
Please help me in solving this issue.
thanks.

Answer 1

As Suggested by #PaulR, clipping was causing a lot of harmonics.
Your waveform is clipping (because 0.8 + 0.8 > 1.0), which will generate a lot of harmonics - look at the data in your debugger and you’ll see lots of flat peaks at +/- 32k.
So, after taking care of this limit. My issue is resolved.
Thanks alot.