creating the chorus effect without using a loop

Question

Damien 2022-11-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1850933-creating-the-chorus-effect-without-using-a-loop

评论： Mathieu NOE 2022-11-17

okay so I made some progress but I am still lost and im not sure what sound I am suppose to hear back. There are not any helpful youtube videos about this topic.. but now I am hearing a static noise for about 3 seconds. Please if anyone can look at my updated code and help me out so I can see what I am doing wrong. Do it for a veteran :)

[x,Fs]=audioread('slowguitar.wav');
sound(x, Fs);
n=44100;
D=round(Fs*40e-3);
x=rand(1,n);
y=zeros(1,n);
y(1)=x(1);
y(2:n) =x(2:n)+x(n-D);
sound(y(2:n), Fs);

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Paul 2022-11-15

Hi Damien,

I don't know what the chorus effect is, so don't know how it should be implemented. If it can be explained, preferably in mathematical terms, it's likely someone could help implement it in Matlab.

In the above code, the variable x is an output from audioread, but four lines later it's overwritten with random numbers. Is that correct?

Damien 2022-11-15

Thank you, I fixed this but still no luck in obtaining the desired result.

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Answer 1

Mathieu NOE 2022-11-15

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1850933-creating-the-chorus-effect-without-using-a-loop#answer_1100468

在 MATLAB Online 中打开

DirectGuitar.zip

hello

the chorus effect is basically a multiple echo effect ; the echo by itself is a delayed version of the original signal , added to it with a given amplitude (therefore you can tweak the delay and amount of the echo)

when you have understood the echo principle , apply it multiple times and here you have a chorus effect (like many people singing at different distance from the listening point, causing different delays and amplitudes)

the code below is for a wav file (attached if you want to try it) but you can easily modify it at your convenience

infile='DirectGuitar.wav';
outfile='out_chorus.wav';
% current sample is 11kHz so 0-3 ms is 0 - 33 samples
% read the sample waveform
[x,Fs] = audioread(infile);
% normalize x to +/- 1 amplitude
x = x ./ (max(abs(x)));
samples = length(x);
nb_effects = 4; % assume we do 4 delayed versions of the signal that will be summed 
% amplitude is now a vector
amp = [0.7 0.7 0.7 0.7]; % suggested coefficient from page 71 DAFX; the  values apply to the 4 delayed versions of x
cur_delay = [134;248;422;13];       % fixed delay case
max_samp_delay=max(cur_delay); 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
y = x;       % init y
for i = (max_samp_delay+1):samples
    % add the amp weigthed multiple delayed x values
    y(i) = x(i) + sum(amp(1:nb_effects)'.*x(i-cur_delay));   % add all 4 delayed sample (in one line !)
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('Chorus and Original Signal');
legend('Original','Chorus');
sound(y,Fs);

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Mathieu NOE 2022-11-16

在 MATLAB Online 中打开

Ok why not...

the price to pay is that you have to manually create as many variables as there are delayed versions of the signal

here y1 , y2 , y3 and y 4 are the four delayed versions of the input signal. Each one has individual delay and amplitude.

code with zero for loop :

infile='DirectGuitar.wav';
outfile='out_chorus.wav';
% current sample is 11kHz so 0-3 ms is 0 - 33 samples
% read the sample waveform
[x,Fs] = audioread(infile);
% normalize x to +/- 1 amplitude
x = x ./ (max(abs(x)));
samples = length(x);
nb_effects = 4; % assume we do 4 delayed versions of the signal that will be summed 
% amplitude is now a vector
amp = [0.7 0.7 0.7 0.7]; % suggested coefficient from page 71 DAFX; the  values apply to the 4 delayed versions of x
cur_delay = [134;248;422;13];       % fixed delay case
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% y1, y2 , y3, y4 are the four delayed version of x (and scaled with
% "amp" amplitude);
y1 = zeros(size(x)); % init
y1(cur_delay(1)+1:samples) = amp(1)*x(1:samples-cur_delay(1));
y2 = zeros(size(x)); % init
y2(cur_delay(2)+1:samples) = amp(2)*x(1:samples-cur_delay(2));
y3 = zeros(size(x)); % init
y3(cur_delay(3)+1:samples) = amp(3)*x(1:samples-cur_delay(3));
y4 = zeros(size(x)); % init
y4(cur_delay(4)+1:samples) = amp(4)*x(1:samples-cur_delay(4));
y = x + y1 + y2 + y3 + y4; % sum all signals
% normalize y to +/- 1 amplitude for wav export
y = y ./ (max(abs(y)));
audiowrite(outfile, y, Fs);
figure(1)
hold on
plot(x,'r');
plot(y,'b');
title('Chorus and Original Signal');
legend('Original','Chorus');
sound(y,Fs);