Myujth

I am trying to perform the STFT on a speech signal. I'd like to know when I should do the zero-padding, before windowing each frame, or after?

My attempt:

x = signal(:); % make sure signal is a column vector
sL = length(x); % signal length
wL = fix(window_Time*fs); % window length
HOP = floor(wL*(1 - overlap/100)); % windowing step 
win = gausswin(wL); % window type
F = 1 + fix((sL-wL)/HOP); % calculate the number of signal frames
stft = zeros(nfft,F); % preallocate stft matrix, [nfftxF]

for f = 0:F-1
 xw = x(1+f*HOP:wL+f*HOP).*win; % windowing
 X = fftshift(fft([xw;zeros(wL,1)],nfft)); % FFT shifted (double-sided)
 stft(:,1+f) = X; % update of the stft matrix
end

You must do it before the FFT.

1. Divide the signal into frames, see butter function;


2. Apply a window to each frames: frames x window;


3. Zero-padd the signal;


4. FFT each windowed frames.

P.S. I've read somewhere that the FFT algorithm already does the zero-padding automatically, i.e., When you to the FFT(x) it will already “padd” the signal x with zeros at the end, to reach the length of the FFT.

You zero pad frames inside window after windowing to make the window length the power of 2