FFT and changing frequency and vectorizing for loop

[Rick T]

FFT and changing frequency and vectorizing for loop

Greetings All

I can increase and decrease the frequency of the

signal using the combination of fft and a series expansion for loop in the code below

but if the signal/array is to large it becomes extremely

slow (an array that's 1x44100 takes about 2 mins to complete) I'm sure it has to do with the for loop but

I'm not exactly sure how to vectorize them to improve performance

Any recommendations

tia sal22 

%create signal

clear all, clc,clf,tic

x= linspace(0,2*pi,44100)'; 

%Used in exporting to ycalc audio file make sure in sync with above

freq_orig=1;

freq_new=4

vertoff=0;

vertoffConj=0;

vertoffInv=0;

vertoffInvConj=0;

phaseshift=(0)*pi/180 ; %can use mod to limit to 180 degrees

y=sin(freq_orig*(x)); 

[size_r,size_c]=size(y);

N=size_r; %to test make 50

T=2*pi;

dt=T/N;

t=linspace(0,T-dt,N)';

phase = 0;

f0 = 1/T; % Exactly, one period 

y=(y/max(abs(y))*.8)/2; %make the max amplitude here

C = fft(y)/N; % No semicolon to display output

 

A = real(C); 

B = imag(C)*-1; %I needed to multiply by -1 to get the correct sign

% Single-Sided (f >= 0) 

An = [A(1); 2*A(2:round(N/2)); A(round(N/2)+1)]; %needed to put the ' to get vaules in rows 

Bn = [B(1); 2*B(2:round(N/2)); B(round(N/2)+1)]; %needed to put the ' to get vaules in ro

pmax=N/2;

ycalc=zeros(N,1); %preallocating space for ycalc

w=0;

for p=2:pmax

                %

        %%1 step) re-create signal using equation 

         ycalc=ycalc+An(p)*cos(freq_new*(p-1).*t-phaseshift)+Bn(p)*sin(freq_new*(p-1).*t-phaseshift)+(vertoff/pmax);

         w=w+(360/(pmax-1)); %used to create phaseshift

         phaseshift=w;

        

end;

fprintf('\n- Completed in %4.4fsec or %4.4fmins\n',toc,toc/60);

subplot(2,1,1), plot(y),title('Orginal Signal'); 

subplot(2,1,2),plot(ycalc),title('FFT new signal'); 

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