fir_test.m
1.3 KB
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% 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