fir_test.m
1.95 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
% -----------------------------------------------------------------------------
% Copyright (C) 2019-2021 daiteq s.r.o. http://www.daiteq.com
%
% This program is distributed WITHOUT ANY WARRANTY; without even
% the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
% PURPOSE.
%
% -----------------------------------------------------------------------------
% Filename : fir_test.c
% Authors : Roman Bartosinski
% Description : FIR filter - reference Octave implementation
% Release :
% Version : 1.0
% Date : 27.4.2021
% -----------------------------------------------------------------------------
%
% Signal generation
sample_rate = 48000;
nsamples = 256;
F = [1 15] * 1000;
A = [1 0.5];
% Time vector - use colon operator to generate integer vector of sample numbers
t = (0:nsamples-1) / sample_rate;
% Test signal - use matrix notation to compose it with single expression
signal = A * sin(2*pi*F'*t);
% FIR coefficient generation
% Choose filter cutoff frequency (6 kHz)
cutoff_hz = 6000;
% Normalize cutoff frequency (wrt Nyquist frequency)
nyq_freq = sample_rate / 2;
cutoff_norm = cutoff_hz / nyq_freq;
% FIR filter order (i.e. number of coefficients - 1)
order = 24;
% Create lowpass FIR filter through a direct approach
% NOTE: fir1, firpmord and firpm all require Signal Processing Toolbox
fir_coeff = fir1(order, cutoff_norm);
% Analyse the filter using the Filter Visualization Tool
%fvtool(fir_coeff, 'Fs', sample_rate)
% Filter the signal with the FIR filter
filtered_signal = filter(fir_coeff, 1, signal);
% Convert to 8-bit integer version
conv_scale = 92
sig8b = int8(signal*conv_scale);
printf("signal = [");
printf("%d,",sig8b);
printf("];\n");
fir8b = int8(fir_coeff*conv_scale);
printf("fir_coeff = [");
printf("%d,",fir8b);
printf("];\n");
filtsig8b = filter(fir8b, 1, sig8b);
printf("filt_signal = [");
printf("%d,",filtsig8b);
printf("];\n");
% filtsig8b is multiplied by conv_scale^2