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 for the GUI part.

Any suggestions? Thanks.

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))

Answer 2

"How do I create a frequency vs time plot?" lists several libraries, each of which can calculate a spectrogram from a signal.

Copied and pasted from my own answer:

Some source code to generate spectrograms / waterfall plots from audio data:

• SoX - Sound eXchange includes spectrogram source code
• Audacity includes spectrogram source code
• glfer includes waterfall spectrum display spectrum source code
• source code that uses fftw to compute the spectrogram of an audio stream
• more source code that uses OpenAL and fftw to compute the spectrogram for an audio stream
• "Sound Activated Recorder with Spectrogram in C#" by Jeff Morton
• Topographica seems to include spectrogram source code
• SpectroGraph for iTunes

Image to Spectrogram goes in the reverse direction from the above utilities.

Answer 3

you could use fftw (fftw.org) to calculate the spectrogram, you would still need to plot the data, but that should not be a problem

Answer 4

You can use FFT code from here. It uses C++ template metaprogramming for efficiency. The full source is provided by the author here.

It was suggested to include this code into Eigen for its use of templated (type friendly) code.