Calculates the 2D Spectrogram as a B&W image.
SONOGRAM(series, len, overlap, swin)
series 
 
An input series 

len 
 
Optional. An integer, the segment length. Defaults to 512. 

overlap 
 
Optional. An integer, the number of points to overlap each segment. Defaults to len/2. 

swin 
 
Optional. An integer, the windowing function

A table of Amplitude values in Frequency vs Time format.
sonogram(W1, 128)
divides W1 into columns of 128 points that overlap by 64 points. Each segment is multiplied by a Hamming window. The spectrum (i.e. magnitude of the FFT) of each column is calculated and the result is displayed as a Black on White image.
See the related SPECGRAM function for more details.