I meet some problem in my coursera homework Echo Generator

Write a function called echo_gen that adds an echo effect to an audio recording. The function is to be called like this:

output = echo_gen(input, fs, delay, amp);

where input is a column vector with values between -1 and 1 representing a time series of digitized sound data. The input argument fs is the sampling rate. The sampling rate specifies how many samples we have in the data each second. For example, an audio CD uses 44,100 samples per second. The input argument delay represent the delay of the echo in seconds. That is, the echo should start after delay seconds have passed from the start of the audio signal. Finally, amp specifies the amplification of the echo which normally should be a value less than 1, since the echo is typically not as loud as the original signal.

The output of the function is a column vector containing the original sound with the echo superimposed. The output vector will be longer than the input vector if the delay is not zero (round to the nearest number of points needed to get the delay, as opposed to floor or ceil). A sound recording has values between -1 and 1, so if the echo causes some values to be outside of this range, you will need to normalize the entire vector, so that all values adhere to this requirement.

MATLAB has several sample audio files included that you can try: splat, gong, and handel are a few examples. Try the following:

load gong % loads two variables, y and Fs

sound(y, Fs) % Outputs sound

To hear the sound you will need to use desktop MATLAB or MATLAB Online.

(Note that we are assuming mono audiofiles. You can load your own audio files using the audioread function

Opens in new tab

in MATLAB. If the audio data has two columns, it is a stereo file, so use only one column of the data when testing your file.)

Code to call your function

% Load splat which adds y and Fs to the workspace
load splat
% Call echo_gen to create the new audio data
output = echo_gen(y, Fs, 0.25, 0.6);

% Create a time axis. The time between points is 1/Fs;
dt = 1/Fs;
t = 0:dt:dt*(length(output)-1);
% Plot the new data to see visualize the echo
plot(t, output)

% sound (newY, Fs) % Uncomment in MATLAB to listen to the new sound data

here is my code

function [output]= echo_gen(input,fs,delay,amp)

[r,c] = size(input);
add = round(delay*fs);
vdm = zeros(r+add,1);
otp = vdm;
for i=1:r
    vdm(i+add,1) =input(i,1)*amp ;
    otp(i) = input(i);
end

otp = otp+vdm;
jugg = abs(otp) ;
t = max(jugg,[],2);
if t>1
    otp = otp/t;
end

output = otp ;

end

Can anyone please tell me where I am going wrong with the code for this question? I have no idea how to solve the problem .

Answer 1

[Steven Lord]

I'm going to comment on individual pieces of your code to offer suggestions and avenues for investigation.

function [output]= echo_gen(input,fs,delay,amp)
[r,c] = size(input);
add = round(delay*fs);
vdm = zeros(r+add,1);
otp = vdm;

I'm not that familiar with audio processing, so I don't know if "vdm" and "otp" are technical terms of art in that area, but I'd encourage you to use longer, more descriptive names. This may help you and people reading your code in the future understand what your code is doing. If I understand your code correctly, I'd call vdm something like echoSignal and otp something like originalSignal. [If you're worried about typing long names over and over, tab completion can help with that.]

Adding comments describing the purpose of each step (not so much what the code is doing, but why it's doing what it's doing) may also help you keep track of your algorithm. So the comment for this line:

vdm = zeros(r+add,1);

wouldn't be just "Creates a zeros vector" but "Create the vector to store the echo". This may feel redundant if you renamed variables to something like:

echoSignal = zeros(r + extraEchoTime, 1);

but you could write the comments describing the steps in the algorithm before you write your code which could help you break your problem into manageable pieces.

for i=1:r
    vdm(i+add,1) =input(i,1)*amp ;
    otp(i) = input(i);
end
otp = otp+vdm;
jugg = abs(otp) ;
t = max(jugg,[],2);

Since jugg is a vector, you don't really need the dimension argument in your call to max.

if t>1
    otp = otp/t;

If t is greater than 1, you never assign a value to the variable output and so MATLAB should throw an error.

Also how do you define "normalization"? Is it division by the maximum absolute value of elements in your array, or is it more along the lines of the 'range' option for the normalize function? Using the "Scale Data" example on that page, which of the following should the "normalization" of A be?

A = 1:5;
bingnanNormalization = A./max(abs(A))
rangeNormalization = normalize(A, 'range', [-1 1])

One final suggestion: as the assignment suggests, "% sound (newY, Fs) % Uncomment in MATLAB to listen to the new sound data". Play the unaltered sound and the sound with the echo and see if it sounds to your ear like there's an echo. If it doesn't, perhaps the way the altered sound sounds will give you a clue as to what's wrong.

[bingnan lee]

Thank you for your suggestion first ,they are all very useful and helpful .And i wil remember that name the variable more descriptive and be more careful during coding, I am not very good at english so when spelling long word i often make mistakes. here is my code after modified ，and i have passed all the tests

function [output]= echo_gen(input,fs,delay,amp)

[r,c] = size(input);
extraEchoTime = round(delay*fs);
echoSignal = zeros(r+extraEchoTime,1);
addEchoSignal = echoSignal ;

for i=1:r
    echoSignal(extraEchoTime+i,1) =input(i,1)*amp ;
    addEchoSignal(i) = input(i);
end

addEchoSignal = addEchoSignal + echoSignal ;

range = abs(addEchoSignal) ;

maxrange = max(range);
if maxrange>1
    addEchoSignal = addEchoSignal/maxrange;
end


output = addEchoSignal ;
end

thanks very much for your help again

hope my reply have no grammatical errors

[Shivakarthik Ekambaram]

This is awesome!

[Rohit Patil]

function [output]= echo_gen(input,fs,delay,amp)

[r,c] = size(input);

extraEchoTime = round(delay*fs);

echoSignal = zeros(r+extraEchoTime,1);

addEchoSignal = echoSignal ;

for i=1:r

echoSignal(extraEchoTime+i,1) =input(i,1)*amp ;

addEchoSignal(i) = input(i);

end

addEchoSignal = addEchoSignal + echoSignal ;

range = abs(addEchoSignal) ;

maxrange = max(range);

if maxrange>1

addEchoSignal = addEchoSignal/maxrange;

end

output = addEchoSignal ;

end

[Faraz Ahmad]

Thanks a lot

[Sana Hafeez]

@bingnan lee Please help me to find out the correct code of image blur

I am stuck now!

[Steven Lord]

This doesn't look like it's related to the original question about creating a function to add an echo to an audio recording so you should ask it as a new question with a descriptive subject, the code pasted into the question rather than posted as a picture (since it's hard to run a picture), a clear description of what the code is intended to do, and a clear statement of the specific problem you're experiencing when trying to run this code.

Answer 2

[Prashant Dubey]

function output = echo_gen(s, Fs, delay, amp)
    % Find the time between points using Fs
    dt = 1/Fs;
    % Calculate the number of points for the given delay
    N = round(delay/dt);
    % Pad the original signal with zeros to make room for the echo
    s1 = [s; zeros(N, 1)];
    % Create an echo signal that starts with 0's
    s2 = [zeros(N, 1); s.*amp];
    % Add the echo to the original signal
    output = s1 + s2;
    % the abs of all values must be < 1. Rescale if necessary
    if max(abs(output)) > 1
        output = output./max(abs(output));
    end
    
    % Note: This only works with column vectors - can you make the
    % function more robust so that it works with column or row vectors?
end
    

[Prashant Dubey]

This is the solution of this problem

[Mark Honey Ancheta]

this!!

Answer 3

[Abdul Quadir Khan]

function [output]= echo_gen(input,fs,delay,amp)

[r,c] = size(input);
extraEchoTime = round(delay*fs);
echoSignal = zeros(r+extraEchoTime,1);
addEchoSignal = echoSignal ;

for i=1:r
    echoSignal(extraEchoTime+i,1) =input(i,1)*amp ;
    addEchoSignal(i) = input(i);
end

addEchoSignal = addEchoSignal + echoSignal ;

range = abs(addEchoSignal) ;

maxrange = max(range);
if maxrange>1
    addEchoSignal = addEchoSignal/maxrange;
end


output = addEchoSignal ;
end

Answer 4

[zaber mhamud]

function output = echo_gen(input,fs,delay,amp)
    sounds = round(fs * delay) ;
    ds = floor(sounds);
    sig = zeros(length(input) + ds, 1);
    sig(1:length(input)) = input;
    e_sig = zeros(length(input) + ds, 1);
    e_sig(ds + (1:length(input*amp))) = input * amp;
    output = sig + e_sig;
    maxx = max(abs(output));
    if maxx > 1
        output = output ./ maxx;
    end
end