Difference between revisions of "Adding sound effects to your music" - Rhea

Revision as of 22:15, 29 November 2015

1.Introduction

Sound effects as echo, flanger and chorus are largely implemented in sound productions. In this section, you will learn the fundamental ideas of each sound effect and use the signal processing technique in Matlab to create these sound effect to your music.

2.Echo effect

The echo effect can be simply considered as a delay of music signal. It is produced by repeating the original music signal after a fixed amount of time period. This effect is extremely applied in microphones and stereos. A FIR filter with a single delay will achieve this effect. The difference equation for the FIR filter can be written as follows:

  			Y[n] = X[n] + a * X[n – D]

Where:

X[n] : input signal

Y[n]: output signal

D : number of samples during delay, fixed value

a : attenuation coefficient. |a| < 1

% Matlab code

[x,fs] = wavread(‘singsing.wav’);  % load the music and get the sampling frequency

length = size(x);  % get the length of the music file

a = 0.3;  % set the attenuation factor

delay = 0.38;

D = delay*fs;  % set the delay time in s

y = zeros(length);  % initialize the output music signal

for i = D + 1 : 1 : length;

	y(i) = x(i) + a*x(i-D);

end;

sound(y, fs);  % play the echo

3.Flanger effect

The flanging effect is produced by mixing two identical music signals with a varying delay function. Unlike the fixed delay D in the echo effect design, the flanger filter has a non-constant delay D, which changes periodically. The difference equation for this flanger filter can be written as follows:

                       Y[n] = X[n] + a * X[ n – D[n] ]

Where:

X[n] : input signal

Y[n]: output signal

D : periodic delay function

a : attenuation coefficient. |a| < 1

% Matlab code:

[y, fs, nbits] = wavread(file);  %Reading the file

low_n = round(0.0*fs);  %Creating the vector according to which delay is varied

high_n = round(0.0057*fs);

delay_vary_p = 8;

delay_step = (delay_vary_p/4)/(1/fs);

delay_1 = round(linspace(low_n,high_n,delay_step));

delay_2 = round(linspace(high_n,low_n,delay_step));

delay = [delay_1 delay_2];

no_points = length(y(:,1));

n_rep = round(no_points/length(delay));

delay = repmat(delay,1,n_rep);

delay = [delay delay(1:no_points-length(delay))];

out_wav(:,1) = zeros(1,no_points);

out_wav(:,2) = zeros(1,no_points);

for i=1:no_points

   n = i-delay(i);

   if n>0

       out_wav(i,1) = y(i,1)+y(n,1);

       out_wav(i,2) = y(i,2)+y(n,2);

   else

       out_wav(i,1) = y(i,1);

       out_wav(i,2) = y(i,2);

   end

end

Referrence

[1] Ingle, V., & Proakis, J. (2000). Digital signal processing using MATLAB. Pacific Grove, CA: Brooks/Cole.

[2] McGovern, S. (2004, December 30). Flange Effect - File Exchange - MATLAB Central. Retrieved November 30, 2015, from http://www.mathworks.com/matlabcentral/fileexchange/6656-flange-effect