Create spectrum from KissFFT and QAudioProbe - c++

Question

I'm trying to create a simple spectrum via QAudioProbe but my spectrum does not "feel the beat". every bin in spectrum just goes high and low.
Here is my code processing buffer from QAudioProbe :
void Waveform::bufferReady(QAudioBuffer buffer){
int n = buffer.frameCount();
cfg = kiss_fft_alloc(n, 0/*is_inverse_fft*/, NULL, NULL);
QAudioBuffer::S16U *frames = buffer.data<QAudioBuffer::S16U>();
qDeleteAll(m_finalData);
m_finalData.clear();
kiss_fft_cpx output[n],input[n];
for (int i=0; i < n; i++)
{
// frames[i].right contains the i-th sample from the right channel
// frames[i].left contains the i-th sample from the left channel
// if the signal is mono and not stereo, then only one of the channels will have data
qreal hanawindow = 0.5 * (1 - qCos((2 * M_PI * i) / (n - 1)));
input[i].r = frames[i].right * hanawindow; // WindowFunction
input[i].i = 0;
}
kiss_fft(cfg, input, output); // DO FFT
int step = n/(2*60); // distance to take value for bin from list. Here is 60bins
for(int i=0; i< n/2;i+=step){
qreal magnitude = qSqrt(output[i].i*output[i].i + output[i].r*output[i].r);
qreal amplitude = 0.15 * log10(magnitude);
amplitude = qMax(qreal(0.0), amplitude);
amplitude = qMin(qreal(1.0), amplitude);
m_finalData.append(new Sample(amplitude));
}
qDebug() << "Number of Bins : " << m_finalData.count();
emit dataReady();
}
I don't know what are problems with the above code. I've been trying a lot of other ways but the spectrum still weird.