Spectrogram C++ library

Question

For my current project in C++ / Qt I need a library (LGPL is preferred) which can calculate a spectrogram from a signal ( basically an array of doubles ). I already use Qwt

Answer 1

It would be fairly easy to put together your own spectrogram. The steps are:

1. window function (fairly trivial, e.g. Hanning)
2. FFT (FFTW would be a good choice but if licensing is an issue then go for Kiss FFT or similar)
3. calculate log magnitude of frequency domain components (trivial: log(sqrt(re * re + im * im))