mirror of https://github.com/g4klx/MMDVM.git
46 lines
1.1 KiB
Python
46 lines
1.1 KiB
Python
# based on https://github.com/berndporr/iir_fixed_point/blob/master/gen_coeff.py
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import numpy as np
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import scipy.signal as signal
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import pylab as pl
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# Calculate the coefficients for a pure fixed point
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# integer filter
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# sampling rate
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fs = 24000
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# cutoffs
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f1 = 300
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f2 = 2700
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# ripple
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rp = 0.2
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# scaling factor in bits, do not change !
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q = 15
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# scaling factor as facor...
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scaling_factor = 2**q
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# let's generate a sequence of 2nd order IIR filters
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sos = signal.cheby1(3,rp,[f1, f2],'bandpass', output='sos', fs=fs)
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#os = signal.cheby1(4, rp, f2, 'lowpass', output='sos', fs=fs) #deemphasis filter
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#sos = signal.cheby1(1, rp, 2122, 'highpass', output='sos', fs=fs) #deemphasis filter
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sosrounded = np.round((sos) * scaling_factor)
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# print coefficients
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for biquad in sosrounded:
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for coeff in biquad:
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print(int(coeff),",",sep="",end="")
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#print((coeff),",",sep="",end="")
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print("")
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# plot the frequency response
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b,a = signal.sos2tf(sos)
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w,h = signal.freqz(b,a, worN=2048)
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pl.plot(w/np.pi/2*fs,20*np.log(np.abs(h)))
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pl.xlabel('frequency/Hz');
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pl.ylabel('gain/dB');
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pl.ylim(top=1,bottom=-30);
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pl.xlim(left=250, right=12000);
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pl.show() |