Nicolas Borla / Mbed OS BBR_1Ebene

BBR 1 Ebene

mbed-os/tools/dev/dsp_fir.py@0:fbdae7e6d805, 2018-05-14 (annotated)

Committer:
borlanic
Date:
Mon May 14 11:29:06 2018 +0000
Revision:
0:fbdae7e6d805
BBR

Who changed what in which revision?

UserRevisionLine numberNew contents of line
borlanic 0:fbdae7e6d805 1 """
borlanic 0:fbdae7e6d805 2 mbed SDK
borlanic 0:fbdae7e6d805 3 Copyright (c) 2011-2013 ARM Limited
borlanic 0:fbdae7e6d805 4
borlanic 0:fbdae7e6d805 5 Licensed under the Apache License, Version 2.0 (the "License");
borlanic 0:fbdae7e6d805 6 you may not use this file except in compliance with the License.
borlanic 0:fbdae7e6d805 7 You may obtain a copy of the License at
borlanic 0:fbdae7e6d805 8
borlanic 0:fbdae7e6d805 9 http://www.apache.org/licenses/LICENSE-2.0
borlanic 0:fbdae7e6d805 10
borlanic 0:fbdae7e6d805 11 Unless required by applicable law or agreed to in writing, software
borlanic 0:fbdae7e6d805 12 distributed under the License is distributed on an "AS IS" BASIS,
borlanic 0:fbdae7e6d805 13 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
borlanic 0:fbdae7e6d805 14 See the License for the specific language governing permissions and
borlanic 0:fbdae7e6d805 15 limitations under the License.
borlanic 0:fbdae7e6d805 16 """
borlanic 0:fbdae7e6d805 17 from numpy import sin, arange, pi
borlanic 0:fbdae7e6d805 18 from scipy.signal import lfilter, firwin
borlanic 0:fbdae7e6d805 19 from pylab import figure, plot, grid, show
borlanic 0:fbdae7e6d805 20
borlanic 0:fbdae7e6d805 21 #------------------------------------------------
borlanic 0:fbdae7e6d805 22 # Create a signal for demonstration.
borlanic 0:fbdae7e6d805 23 #------------------------------------------------
borlanic 0:fbdae7e6d805 24 # 320 samples of (1000Hz + 15000 Hz) at 48 kHz
borlanic 0:fbdae7e6d805 25 sample_rate = 48000.
borlanic 0:fbdae7e6d805 26 nsamples = 320
borlanic 0:fbdae7e6d805 27
borlanic 0:fbdae7e6d805 28 F_1KHz = 1000.
borlanic 0:fbdae7e6d805 29 A_1KHz = 1.0
borlanic 0:fbdae7e6d805 30
borlanic 0:fbdae7e6d805 31 F_15KHz = 15000.
borlanic 0:fbdae7e6d805 32 A_15KHz = 0.5
borlanic 0:fbdae7e6d805 33
borlanic 0:fbdae7e6d805 34 t = arange(nsamples) / sample_rate
borlanic 0:fbdae7e6d805 35 signal = A_1KHz * sin(2*pi*F_1KHz*t) + A_15KHz*sin(2*pi*F_15KHz*t)
borlanic 0:fbdae7e6d805 36
borlanic 0:fbdae7e6d805 37 #------------------------------------------------
borlanic 0:fbdae7e6d805 38 # Create a FIR filter and apply it to signal.
borlanic 0:fbdae7e6d805 39 #------------------------------------------------
borlanic 0:fbdae7e6d805 40 # The Nyquist rate of the signal.
borlanic 0:fbdae7e6d805 41 nyq_rate = sample_rate / 2.
borlanic 0:fbdae7e6d805 42
borlanic 0:fbdae7e6d805 43 # The cutoff frequency of the filter: 6KHz
borlanic 0:fbdae7e6d805 44 cutoff_hz = 6000.0
borlanic 0:fbdae7e6d805 45
borlanic 0:fbdae7e6d805 46 # Length of the filter (number of coefficients, i.e. the filter order + 1)
borlanic 0:fbdae7e6d805 47 numtaps = 29
borlanic 0:fbdae7e6d805 48
borlanic 0:fbdae7e6d805 49 # Use firwin to create a lowpass FIR filter
borlanic 0:fbdae7e6d805 50 fir_coeff = firwin(numtaps, cutoff_hz/nyq_rate)
borlanic 0:fbdae7e6d805 51
borlanic 0:fbdae7e6d805 52 # Use lfilter to filter the signal with the FIR filter
borlanic 0:fbdae7e6d805 53 filtered_signal = lfilter(fir_coeff, 1.0, signal)
borlanic 0:fbdae7e6d805 54
borlanic 0:fbdae7e6d805 55 #------------------------------------------------
borlanic 0:fbdae7e6d805 56 # Plot the original and filtered signals.
borlanic 0:fbdae7e6d805 57 #------------------------------------------------
borlanic 0:fbdae7e6d805 58
borlanic 0:fbdae7e6d805 59 # The first N-1 samples are "corrupted" by the initial conditions
borlanic 0:fbdae7e6d805 60 warmup = numtaps - 1
borlanic 0:fbdae7e6d805 61
borlanic 0:fbdae7e6d805 62 # The phase delay of the filtered signal
borlanic 0:fbdae7e6d805 63 delay = (warmup / 2) / sample_rate
borlanic 0:fbdae7e6d805 64
borlanic 0:fbdae7e6d805 65 figure(1)
borlanic 0:fbdae7e6d805 66 # Plot the original signal
borlanic 0:fbdae7e6d805 67 plot(t, signal)
borlanic 0:fbdae7e6d805 68
borlanic 0:fbdae7e6d805 69 # Plot the filtered signal, shifted to compensate for the phase delay
borlanic 0:fbdae7e6d805 70 plot(t-delay, filtered_signal, 'r-')
borlanic 0:fbdae7e6d805 71
borlanic 0:fbdae7e6d805 72 # Plot just the "good" part of the filtered signal. The first N-1
borlanic 0:fbdae7e6d805 73 # samples are "corrupted" by the initial conditions.
borlanic 0:fbdae7e6d805 74 plot(t[warmup:]-delay, filtered_signal[warmup:], 'g', linewidth=4)
borlanic 0:fbdae7e6d805 75
borlanic 0:fbdae7e6d805 76 grid(True)
borlanic 0:fbdae7e6d805 77
borlanic 0:fbdae7e6d805 78 show()
borlanic 0:fbdae7e6d805 79
borlanic 0:fbdae7e6d805 80 #------------------------------------------------
borlanic 0:fbdae7e6d805 81 # Print values
borlanic 0:fbdae7e6d805 82 #------------------------------------------------
borlanic 0:fbdae7e6d805 83 def print_values(label, values):
borlanic 0:fbdae7e6d805 84 var = "float32_t %s[%d]" % (label, len(values))
borlanic 0:fbdae7e6d805 85 print "%-30s = {%s}" % (var, ', '.join(["%+.10f" % x for x in values]))
borlanic 0:fbdae7e6d805 86
borlanic 0:fbdae7e6d805 87 print_values('signal', signal)
borlanic 0:fbdae7e6d805 88 print_values('fir_coeff', fir_coeff)
borlanic 0:fbdae7e6d805 89 print_values('filtered_signal', filtered_signal)