Time and Frequency domain variable delay filter implementation

Dear friends, I am working towards developing a variable delay filter (FLANGER) in time and frequency domain and compare the performance and quality. Currently I have the time domain filtering working fine with following code....

clc; clear all; close all;

% BASIC FLANGER y(n) = x(n) + gx[n - M(n)]

[x,Fs] = audioread('guit.mp3');
x = x(:,1);

% CONTROLLING PARAMETERS
delay=0.003;        % 3ms max delay in seconds
depth = delay;       % Amount of depth 
modRate = 2;        % rate of flange in Hz
FeedBack = 1;       % MIX control. Original signal strength
FlangAmp = 0.5 ;    % MIX control. Flanged signal strength

% Change to samples
DELAY = round(delay*Fs); % delay in samples
DEPTH = round(depth*Fs); % mod. depth in samples
MODF = modRate/Fs; % modulation frequency in samples

if DEPTH>DELAY 
  error('Depth cant be greater than Delay . max depth =< delay, min depth = 0');
  return;
end

LEN=length(x);              % Samples in input file
DLEN=2+DELAY+DEPTH*2;       % Length of the entire delay  
Delayline=zeros(DLEN,1);    % Vector for delay line
y=zeros(size(x));           % Output vector

for n=1:(LEN)
   MOD = (sin(MODF*2*pi*n));
   TAP= 1+DELAY+DEPTH*MOD;
   F(n)= 1+DELAY+DEPTH*abs(MOD);
   %TAP(n)=1+DELAY+DEPTH*MOD(n);
   i= floor(TAP);
   frac= TAP-i;
   Delayline= [x(n);Delayline(1:DLEN-1)]; 
   %Linear Interpolation
   y(n)= Delayline(i+1)*frac+Delayline(i)*(1-frac);
end
% construct the output signal with MIX controls.
out = FeedBack*x + FlangAmp*y;
sound(out, Fs);

This produces a nice controllable delay effect as desired. Can i improve the performance of this filter in any way ?? to perform faster and/or better quality.

Also, trying to implement this in frequency domain is giving me horrific results. sounds more like a distortion than flanger. here is the code im trying with ... following above section ..

lfo = (F);
Y = (fft(x));
y2 = abs(Y);
a = lfo' .*  Y ;            
b = real(ifft(a));
sound(b,Fs);

Could you kindly advise me what exactly am i doing wrong ?? Do i have to use windowing before multiplication here? if yes, how would i control the variable delay.

Thanks :)

Answer 1

[Sachin Kumar]

nfft = 2^nextpow2(2*LEN);
fax = Fs*(-nfft/2:nfft/2-1)'/nfft;
shft = exp(-1j*delay*2*pi*fax);     % w=2*pi*fax,, Frequency function for delay
fsd = fft(x(:,1),nfft);             % Take FFT
fsd = fsd.*shft;                    %  Apply delay
dum = ifft(fsd);                    %  Return to time domain           
sd(:,1) = real(dum(1:LEN));
sound(sd,Fs);

Use the above code for frequency domain delay.

https://www.mathworks.com/matlabcentral/answers/29961-delay-using-fft