Echo generation of FIR sytem

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Stephen Dokodzo
Stephen Dokodzo 2021-3-27
评论： Mathieu NOE 2021-4-15
How can I generate some echo to the system above? I was trying this code but no luck.
% Template for the echo cancelling problem
fs = 8000; % sampling frequency (Hz)
f = 400; % sinusoid frequency (Hz)
Tdur = 0.2; % pulse duration (s)
x = pulse(f, Tdur, fs); % Generates a pulse
x = [x zeros(1, 2*length(x))]; % zero pad for processing
n = 0:length(x)-1; % discrete time vector
t = n/fs; % continuous time vector
plot(t, x); % Plot signal
xlabel('Time (s)')
ylabel('Amplitude')
title(sprintf('Original pulse: %.2f Hz', f))
sound(x, fs); % Play the sound
% Zero-pad original pulse
Nzp = floor(fs*Tzp);
nzp = 1:Nzp;
xzp = [x zeros(1,Nzp-length(x))];
figure(2)
plot(nzp/fs,xzp); xlabel('Time (s)'); ylabel('Amplitude');
title(['Original pulse, zero-padded to ' num2str(Tzp,3) ' s'])
pause; sound(xzp);
% Generate echoes
Tdel = 0.1; % echo delay (s)
alpha = 0.5; % echo gain
Ndel = floor(Tdel*fs); % echo delay (samples)
b= [1 zeros(1,Ndel-1) alpha]; a = 1; % filter coefficients
y = filter(b,a,xzp);
figure(3)
plot(nzp/fs,y); xlabel('Time (s)'); ylabel('Amplitude');
title(['Echoed signal, gain = ' num2str(alpha,3)]);
pause; sound(y);
%% Your code goes here
function x = pulse(f, Tdur, fs)
% Sinusoid multiplied by a Hann window function.
% f sinsusoid frequency (Hz)
% Tdur duration (s)
% fs sampling frequency (Hz)
nmax = floor(Tdur*fs); % duration (samples)
n = [1:nmax]; % discrete time index
x = hann(nmax).'.* cos(2*pi*f*n/fs); % waveform samples
end

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采纳的回答

Mathieu NOE
Mathieu NOE 2021-3-29
hello
my code as example :
infile='DirectGuitar.wav';
outfile='out_echo.wav';
% read the sample waveform
[x,Fs] = audioread(infile);
% normalize x to +/- 1 amplitude
x = x ./ (max(abs(x)));
% parameters
N_delay=20; % delay in samples
C = 0.7; % amplitude of direct sound
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
y = zeros(length(x),1); % create empty out vector
y(1:N_delay)=x(1:N_delay); % to avoid referencing of negative samples
% for each sample > N_delay
for i = (N_delay+1):length(x)
y(i) = C*x(i) + (1-C)*(x(i-N_delay)); % add delayed sample
end
% write output
% normalize y to +/- 1 amplitude
y = y ./ (max(abs(y)));
audiowrite(outfile, y, Fs);
figure(1)
hold on
plot(x,'r');
plot(y,'b');
title('Echoed and original Signal');
sound(y,Fs);
  2 个评论
Thiago de Sousa
Thiago de Sousa 2021-4-14
didn't understand it, can you please fix the code given by the question?
Mathieu NOE
Mathieu NOE 2021-4-15
here you are
% Template for the echo cancelling problem
fs = 8000; % sampling frequency (Hz)
f = 400; % sinusoid frequency (Hz)
Tdur = 0.2; % pulse duration (s)
x = pulse(f, Tdur, fs); % Generates a pulse
x = [x zeros(1, 2*length(x))]; % zero pad for processing
n = 0:length(x)-1; % discrete time vector
t = n/fs; % continuous time vector
plot(t, x); % Plot signal
xlabel('Time (s)')
ylabel('Amplitude')
title(sprintf('Original pulse: %.2f Hz', f))
sound(x, fs); % Play the sound
% Zero-pad original pulse
Tzp = 1; %
Nzp = floor(fs*Tzp);
nzp = 1:Nzp;
xzp = [x zeros(1,Nzp-length(x))];
tzp = (0:length(xzp)-1)/fs;
figure(2)
plot(tzp,xzp); xlabel('Time (s)'); ylabel('Amplitude');
title(['Original pulse, zero-padded to ' num2str(Tzp,3) ' s'])
pause; sound(xzp);
% Generate echoes
Tdel = 0.1; % echo delay (s)
alpha = 0.5; % echo gain
Ndel = floor(Tdel*fs); % echo delay (samples)
b= [1 zeros(1,Ndel-1) alpha]; a = 1; % filter coefficients
y = filter(b,a,xzp);
figure(3)
plot(tzp,y); xlabel('Time (s)'); ylabel('Amplitude');
title(['Echoed signal, gain = ' num2str(alpha,3)]);
pause; sound(y);
%% Your code goes here
function x = pulse(f, Tdur, fs)
% Sinusoid multiplied by a Hann window function.
% f sinsusoid frequency (Hz)
% Tdur duration (s)
% fs sampling frequency (Hz)
nmax = floor(Tdur*fs); % duration (samples)
n = [1:nmax]; % discrete time index
x = hann(nmax).'.* cos(2*pi*f*n/fs); % waveform samples
end

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