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Asked: 2026-05-21T16:50:24+00:00

How can I increase/decrease (frequency/pitch) and phase using fft/ifft I think I have the

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How can I increase/decrease (frequency/pitch) and phase using fft/ifft I think I have the basic code but I’m not sure what to do next

I was told repmat and resample may help, yes I want to linear shift all components. I want to adjust the phase over time so that it will create a standing wave. One signal with the phase changing in one direction and another signal with the phase going the opposite direction

PS: It’s done in Octave/matlab code

Example I have a signal that’s repeats 1 time every second and I want to have it repeat 3 times a second instead. 

%Voiceprint raise lower freq phase conjugate signal
tic
clear all, clc,clf,tic
%% Sound /beep calculation complete
filerawbeepStr='calculations_complete.wav';
filerawbeeppathStr='/home/rat/Documents/octave/raw/';
filevoiceprepathStr='/home/rat/Documents/octave/eq_research/main/transform/voice/';
filewavpathStr='/home/rat/Documents/octave/eq_research/main/transform/wav/';
[ybeep, Fsbeep, nbitsbeep] = wavread(strcat(filerawbeeppathStr,filerawbeepStr));
%addpath(”/home/rat/Documents/octave/eq_research/main/transform/”); %add path to location of functions

%1a voice print import
[vp_sig_orig, fs_rate, nbitsraw] = wavread(strcat(filevoiceprepathStr,'voice8000fs.wav')); 

%vp_sig_orig=vp_sig_orig’;
vp_sig_len=length(vp_sig_orig);

%2a create frequency domain
ya_fft = fft(vp_sig_orig);
vp_sig_phase_orig = unwrap(angle(ya_fft));

%get Magnitude
ya_fft_mag = abs(ya_fft);

%3a frequency back to time domain
ya_ifft=real(ifft(ya_fft));

%adjust frequency/phase here? How?
vp_sig_new=real(ifft(ya_fft_mag.*exp(i*vp_sig_phase_orig)));

subplot(3,1,1), plot(vp_sig_orig),title('1 original time domain')
subplot(3,1,2), plot(ya_ifft),title('2 rebuild time domain')
subplot(3,1,3), plot(vp_sig_new),title('3 adjusted time')
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1 Answer

  1. Editorial Team

    This is one way to do this but if the signal is large you may have to increase the number of points to the signal

    clear,clc
fs = 44100;                   % Sampling frequency
t=linspace(0,1,fs);
freq=1;
ya = sin(2*pi*freq*t)'; %+ 1*sin(2*pi*250*t); 


num_per_sec=5
yb=repmat(ya,num_per_sec,1);%replicate matrix 
xxo=linspace(0,1,length(yb))'; %go from 0 to 1 sec can change speed by incr/decr 1
xxi=linspace(0,1,length(ya))'; %go from 0 to 1 sec and get total samplerate from total y value
yi_t=interp1(xxo,yb,xxi,'linear');

plot(yi_t)
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