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dev/dsp_fir.py@0:4a2e5f0422d6, 2016-03-30 (annotated)

Committer:
screamer
Date:
Wed Mar 30 16:23:44 2016 +0000
Revision:
0:4a2e5f0422d6
Initial revision

Who changed what in which revision?

UserRevisionLine numberNew contents of line
screamer 0:4a2e5f0422d6 1 """
screamer 0:4a2e5f0422d6 2 mbed SDK
screamer 0:4a2e5f0422d6 3 Copyright (c) 2011-2013 ARM Limited
screamer 0:4a2e5f0422d6 4
screamer 0:4a2e5f0422d6 5 Licensed under the Apache License, Version 2.0 (the "License");
screamer 0:4a2e5f0422d6 6 you may not use this file except in compliance with the License.
screamer 0:4a2e5f0422d6 7 You may obtain a copy of the License at
screamer 0:4a2e5f0422d6 8
screamer 0:4a2e5f0422d6 9 http://www.apache.org/licenses/LICENSE-2.0
screamer 0:4a2e5f0422d6 10
screamer 0:4a2e5f0422d6 11 Unless required by applicable law or agreed to in writing, software
screamer 0:4a2e5f0422d6 12 distributed under the License is distributed on an "AS IS" BASIS,
screamer 0:4a2e5f0422d6 13 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
screamer 0:4a2e5f0422d6 14 See the License for the specific language governing permissions and
screamer 0:4a2e5f0422d6 15 limitations under the License.
screamer 0:4a2e5f0422d6 16 """
screamer 0:4a2e5f0422d6 17 from numpy import sin, arange, pi
screamer 0:4a2e5f0422d6 18 from scipy.signal import lfilter, firwin
screamer 0:4a2e5f0422d6 19 from pylab import figure, plot, grid, show
screamer 0:4a2e5f0422d6 20
screamer 0:4a2e5f0422d6 21 #------------------------------------------------
screamer 0:4a2e5f0422d6 22 # Create a signal for demonstration.
screamer 0:4a2e5f0422d6 23 #------------------------------------------------
screamer 0:4a2e5f0422d6 24 # 320 samples of (1000Hz + 15000 Hz) at 48 kHz
screamer 0:4a2e5f0422d6 25 sample_rate = 48000.
screamer 0:4a2e5f0422d6 26 nsamples = 320
screamer 0:4a2e5f0422d6 27
screamer 0:4a2e5f0422d6 28 F_1KHz = 1000.
screamer 0:4a2e5f0422d6 29 A_1KHz = 1.0
screamer 0:4a2e5f0422d6 30
screamer 0:4a2e5f0422d6 31 F_15KHz = 15000.
screamer 0:4a2e5f0422d6 32 A_15KHz = 0.5
screamer 0:4a2e5f0422d6 33
screamer 0:4a2e5f0422d6 34 t = arange(nsamples) / sample_rate
screamer 0:4a2e5f0422d6 35 signal = A_1KHz * sin(2*pi*F_1KHz*t) + A_15KHz*sin(2*pi*F_15KHz*t)
screamer 0:4a2e5f0422d6 36
screamer 0:4a2e5f0422d6 37 #------------------------------------------------
screamer 0:4a2e5f0422d6 38 # Create a FIR filter and apply it to signal.
screamer 0:4a2e5f0422d6 39 #------------------------------------------------
screamer 0:4a2e5f0422d6 40 # The Nyquist rate of the signal.
screamer 0:4a2e5f0422d6 41 nyq_rate = sample_rate / 2.
screamer 0:4a2e5f0422d6 42
screamer 0:4a2e5f0422d6 43 # The cutoff frequency of the filter: 6KHz
screamer 0:4a2e5f0422d6 44 cutoff_hz = 6000.0
screamer 0:4a2e5f0422d6 45
screamer 0:4a2e5f0422d6 46 # Length of the filter (number of coefficients, i.e. the filter order + 1)
screamer 0:4a2e5f0422d6 47 numtaps = 29
screamer 0:4a2e5f0422d6 48
screamer 0:4a2e5f0422d6 49 # Use firwin to create a lowpass FIR filter
screamer 0:4a2e5f0422d6 50 fir_coeff = firwin(numtaps, cutoff_hz/nyq_rate)
screamer 0:4a2e5f0422d6 51
screamer 0:4a2e5f0422d6 52 # Use lfilter to filter the signal with the FIR filter
screamer 0:4a2e5f0422d6 53 filtered_signal = lfilter(fir_coeff, 1.0, signal)
screamer 0:4a2e5f0422d6 54
screamer 0:4a2e5f0422d6 55 #------------------------------------------------
screamer 0:4a2e5f0422d6 56 # Plot the original and filtered signals.
screamer 0:4a2e5f0422d6 57 #------------------------------------------------
screamer 0:4a2e5f0422d6 58
screamer 0:4a2e5f0422d6 59 # The first N-1 samples are "corrupted" by the initial conditions
screamer 0:4a2e5f0422d6 60 warmup = numtaps - 1
screamer 0:4a2e5f0422d6 61
screamer 0:4a2e5f0422d6 62 # The phase delay of the filtered signal
screamer 0:4a2e5f0422d6 63 delay = (warmup / 2) / sample_rate
screamer 0:4a2e5f0422d6 64
screamer 0:4a2e5f0422d6 65 figure(1)
screamer 0:4a2e5f0422d6 66 # Plot the original signal
screamer 0:4a2e5f0422d6 67 plot(t, signal)
screamer 0:4a2e5f0422d6 68
screamer 0:4a2e5f0422d6 69 # Plot the filtered signal, shifted to compensate for the phase delay
screamer 0:4a2e5f0422d6 70 plot(t-delay, filtered_signal, 'r-')
screamer 0:4a2e5f0422d6 71
screamer 0:4a2e5f0422d6 72 # Plot just the "good" part of the filtered signal. The first N-1
screamer 0:4a2e5f0422d6 73 # samples are "corrupted" by the initial conditions.
screamer 0:4a2e5f0422d6 74 plot(t[warmup:]-delay, filtered_signal[warmup:], 'g', linewidth=4)
screamer 0:4a2e5f0422d6 75
screamer 0:4a2e5f0422d6 76 grid(True)
screamer 0:4a2e5f0422d6 77
screamer 0:4a2e5f0422d6 78 show()
screamer 0:4a2e5f0422d6 79
screamer 0:4a2e5f0422d6 80 #------------------------------------------------
screamer 0:4a2e5f0422d6 81 # Print values
screamer 0:4a2e5f0422d6 82 #------------------------------------------------
screamer 0:4a2e5f0422d6 83 def print_values(label, values):
screamer 0:4a2e5f0422d6 84 var = "float32_t %s[%d]" % (label, len(values))
screamer 0:4a2e5f0422d6 85 print "%-30s = {%s}" % (var, ', '.join(["%+.10f" % x for x in values]))
screamer 0:4a2e5f0422d6 86
screamer 0:4a2e5f0422d6 87 print_values('signal', signal)
screamer 0:4a2e5f0422d6 88 print_values('fir_coeff', fir_coeff)
screamer 0:4a2e5f0422d6 89 print_values('filtered_signal', filtered_signal)