# Audio Pitch Manipulation Through Time

3 views (last 30 days)
Hans Buchele on 30 Sep 2022
Commented: Star Strider on 20 Oct 2022
Dear Community, I recently discovered the possibility to manipulate the pitch of a sine wave by changing the time interval values before the creation (y=sin(2*pi*f*t)) For my new project I would need to manipulate the pitch of an imported audio file in the same way but I can not figure out how to achieve it. Any help is very much appreciated! Thanks!

Star Strider on 30 Sep 2022
I am not certain what you want to do. One option could be the resample: function.
Star Strider on 3 Oct 2022
Edited: Star Strider on 3 Oct 2022
As always, my pleasure!
EDIT — (3 Oct 2022 at 15:12)
Thinking about this further, while the sampling frequency must be kept constant, the intervals in the time vector used to create a specific sound does not.
Example —
Fs = 44100;
t = linspace(0, 3*Fs-1, 3*Fs).'/Fs; % Original Time Vector (Column Vector)
s = @(t) sin(2*pi*t*1000); % Original Sound Function
ts = 0.75*exp(-(t-1.5).^2*25); % 'Warped' Time Vector
th = hypot(t,ts); % Sampling Times Of 'Warped' Time Vector
figure
plot(t,th)
grid
xlabel('Time')
ylabel('Warped Time')
figure
plot(t,s(t))
grid
xlabel('Time')
ylabel('Amplitude')
title('Original Tone')
figure
plot(t,s(th))
grid
xlabel('Time')
ylabel('Amplitude')
title('''Warped'' Tone')
sound(s(t),Fs)
pause(3)
sound(s(th),Fs)
The sampling intervals must be monotonically increasing, and the sound function assumes that they are regularly-spaced, so varying the time intervals (created by taking the hypotenuse of the ‘warped’ time vector) used to calculate the tone frequency causes the frequency to change when the sound is played back. This example uses a Gaussian function to warp the time vector, however any continuouis function will likely work. (Discontinuous functions would create a ‘popping’ sound at the discontinuities, so I do not recommend them.)
.

jibrahim on 20 Oct 2022
you can use shiftPitch for this:
%Read in an audio file and listen to it.
sound(audioIn,fs)
%Increase the pitch by 3 semitones and listen to the result.
nsemitones = 3;
audioOut = shiftPitch(audioIn,nsemitones);
sound(audioOut,fs)
%Decrease the pitch of the original audio by 3 semitones and listen to the result.
nsemitones = -3;
audioOut = shiftPitch(audioIn,nsemitones);
sound(audioOut,fs)
Star Strider on 20 Oct 2022
The shiftPitch function requires the Audio Toolbox.

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