Python - Removing specific frequencies between a range

Question

I have a Spectrogram:

I want to clean the spectrogram up, so I only capture the frequencies within a specific range (i.e. in this example, between 2627 - 3939) and remove all of the blocks that are below this frequency. My overall aim is to only be left with the 4 segments that are within this frequency range, and, can be identified.

Here is my code so far:

import wave, struct, numpy as np, matplotlib.mlab as mlab, pylab as pl
def wavToArr(wavefile):
    w = wave.open(wavefile,"rb")
    p = w.getparams()
    s = w.readframes(p[3])
    w.close()
    sd = np.fromstring(s, np.int16)
    return sd,p

def wavToSpec(wavefile,log=False,norm=False):
    wavArr,wavParams = wavToArr(wavefile)
    print wavParams
    return  mlab.specgram(wavArr, NFFT=256,Fs=wavParams[2],window=mlab.window_hanning,noverlap=128,sides='onesided',scale_by_freq=True)

wavArr,wavParams = wavToArr("4bats.wav")
Pxx, freqs, bins = wavToSpec("4bats.wav")
Pxx += 0.0001

freqs += (len(wavArr) / wavParams[2]) / 2.
hf=pl.figure(figsize=(12,12));
ax = hf.add_subplot(2,1,1);
#plot spectrogram as decibals
hm = ax.imshow(10*np.log10(Pxx),interpolation='nearest',origin='lower',aspect='auto')
hf.colorbar(hm)
ylcnt = len(ax.get_yticklabels())
ycnt = len(freqs)
ylstep = int(ycnt / ylcnt)
ax.set_yticklabels([ int(freqs[f]) for f in xrange(0,ycnt,ylstep) ])
pl.show()

The problem is, I don't know how to do this using Python. I know the ranges (2627 - 3939) but, would I iterate through the entire 2D-array and sum up all the blocks, or, for each block within the Spectrogram, calculate the frequency and if it's higher than the threshold, keep it, otherwise the values become 0.0?

If I sum up each of the bins, I get the following:

I need to keep these blocks, but, want to remove every other block apart from these.

I hope someone can help me!

Answer 1

Maybe you want something like:

Pxx[np.greater(np.sum(Pxx, axis=1), 2955), :] = 0.

or, I might have your axes switched, so also try:

Pxx[:, np.greater(np.sum(Pxx, axis=0), 2955)] = 0.

Or maybe you want something else... I find the question a bit unclear.