Linear filter for echo effect

Question

RoBoTBoY 2021-1-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/719315-linear-filter-for-echo-effect

回答： Mathieu NOE 2021-1-18

采纳的回答： Mathieu NOE

Hello all!

A discrete-time causal filter is described by the following difference equation.

A simple linear filter for simulation of echo-effect can be described by the following equation

How can I represent the above equation in code?

% I'm not sure about that
syms x(n) y(n)  
eq = y(n) == c*x(n)+(1-c)*x(n-P)

Can I use syms function for n x and y.

P and c are known

Also I want to transform from difference equation to tranfer function. Can I use the function ztrans() for that?

Thanks in advance

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Answer 1

Mathieu NOE 2021-1-18

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https://ww2.mathworks.cn/matlabcentral/answers/719315-linear-filter-for-echo-effect#answer_600185

hello

there is a very simple way to implement echo effects - see demo code below

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);