Issue with Windowing and Spectrum methods #240
Description
I'm playing with Essentia and I get some weird results with Windowing and Spectrum algorithms when using AudioLoader.
First Windowing:
In [122]: monoloader = essentia.standard.MonoLoader(filename = 'myfile.wav')
In [123]: audioloader = essentia.standard.AudioLoader(filename = 'myfile.wav')
In [124]: monoloader_audio = monoloader()
In [125]: audioloader_audio, sr, c = audioloader()
In [126]: monoloader_frame = monoloader_audio[0:1024]
In [127]: audioloader_frame = audioloader_audio[0:1024,0]
In [128]: monoloader_frame
Out[128]:
array([ 0.00143437, 0.02502518, 0.04733421, ..., 0.02630696,
0.01281777, -0.00366222], dtype=float32)
In [129]: audioloader_frame
Out[129]:
array([ 0.00143437, 0.02502518, 0.04733421, ..., 0.02630696,
0.01281777, -0.00366222], dtype=float32)
In [130]: w = Windowing(type = 'hann', size=1024)
In [131]: w(monoloader_frame)
Out[131]:
array([-0.00038114, -0.00030989, -0.00022922, ..., -0.0004094 ,
-0.00044366, -0.00042744], dtype=float32)
In [132]: w(audioloader_frame)
Out[132]:
array([-0.00022529, 0. , -0.00018149, ..., 0. ,
-0.00028865, 0. ], dtype=float32)
Both frame are the same, but I get weird windowed data with AudioLoader (one every two value is 0).
Same thing with Spectrum: I get the expected result when using MonoLoader and weird result with AudioLoader: I set the size parameter to 1024, which from the doc is the audio input size.
From a spectrum function I would expect either the whole symmetric magnitude spectrum on 1024 points, or half the spectrum on 513 points. With the Spectrum method I get the whole (symmetric) spectrum on 513 points. What am I missing?
In [4]: import essentia.standard
In [5]: import essentia
In [6]: loader = essentia.standard.AudioLoader(filename = 'myfile.wav')
In [7]: audio, sr, c = loader()
In [8]: spectrum = essentia.standard.Spectrum(size=1024)
In [9]: spectrum.paramValue('size')
Out[9]: 1024
In [10]: s = spectrum(audio[100000:101024, 0])
In [11]: ion()
In [12]: plot(s)
Out[12]: [<matplotlib.lines.Line2D at 0x7f64edf76f10>]