I have a audio sequence that was captured with my microphone. This sequence is represented in a cv::Mat object with 1 row and n columns, where n represents the number of samples (=length) of my audio file.
I want to get the frequency spectrogram using [Discrete Fourier Transform](http://docs.opencv.org/2.4/modules/core/doc/operations_on_arrays.html#dft) in OpenCV. I tried to make some example codes work, but I do not get the image I want to get.
**Edit**
This is the input image (the sound visualized as Mat for OpenCV):
I read each 20 samples (20 pixels in x-direction) and multiply it with a hanning-window-function. Than I do the discrete fourier transform (dft) and get for each 20-sample-window the dft's result:
e.g.:
.
How can I get by multiple of theses images a spectrogram?
Thanks!
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