I appreciate anyone that takes a moment to help me with this problem. I've been banging my head against the keyboard for a while, searching forums and DSP tutorials and I can't figure this problem out.
So I have a WAV file with a 28 sec song/sound that I am trying to convert to frequency range, apply an FIR filter to isolate the 14.5 - 16kHz range. The WAV has a sampling rate of 32 kHz and contains an intermittent buzz that becomes clearer when I drop out all other frequencies besides the 14.5 -16kHz bands.
I have written this sample of python code, and believe I am close to isolating the signal. Its hard to tell.
# read data from file name fn, using low/high for bandpass # low and high frequency cutoffs, and a def filter_frequencies(fn,low=0,high=0): data = wave.open(fn,'rb'); rate = data.getframerate() ntap = (rate / 4) + 1; nyq = rate / 2 low,high = low/nyq,high/nyq chunks = int(data.getnframes()/(rate*4)) ns = b'' if low and high == 0: # lowpass bp = low; pz = True elif high and low == 0: # highpass bp = high; pz = False else: # bandpass bp = [low,high]; pz = False b = firwin(ntap, bp, pass_zero=pz, window='blackman', nyq=nyq) y = b'' for num in range(chunks): # read 4 secs of frames from wav file seg = np.fromstring(data.readframes(rate*4),dtype=np.int8) #seg = np.fromstring(data.readframes(data.getnframes()),dtype=np.int8) # convert frame amplitudes to their frequency values freq = np.fft.rfft(seg) # perform lowpass, highpass or bandpass filter cr = fftconvolve(freq,b,mode='valid') # converts frequencies to binary string y += cr.tostring() data.close() return y
I am a noob to DSP, so again I would really appreciate your help on if I am doing the FFT to inverse FFT correctly.
Below is the code I am using to transform the output from the above function back into WAV bytes format.
def frequency_to_bytes(freq): # invert the Fast Fourier Transform nf = np.fft.irfft(freq) # convert frequencies back to integer values bs = np.ravel(nf).astype(np.int8) return bs.tostring()
P.s. if you have seen this problem before, or know what challenge I am trying to solve, please no spoilers. I have been working on this for a week solid.
edit: added some background links I have been using as reference.