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help enframe

enframe split signal up into (overlapping) frames: one per row. [F,T]=(X,WIN,INC)

Usage:  (1) f=enframe(x,n)     % split into frames of length n

(2) f=enframe(x,hamming(n,’periodic’),n/4)     % use a 75% overlapped Hamming window of length n

(3) frequency domain frame-based processing:

S=…;                              % input signal

OV=2;                               % overlap factor of 2 (4 is also often used)

INC=20;                             % set frame increment in samples

NW=INC*OV;                          % DFT window length

W=sqrt(hamming(NW,’periodic’));     % omit sqrt if OV=4

W=W/sqrt(sum(W(1:INC:NW).^2));      % normalize window

F=rfft(enframe(S,W,INC),NW,2);      % do STFT: one row per time frame, +ve frequencies only

… process frames …

X=overlapadd(irfft(F,NW,2),W,INC);  % reconstitute the time waveform (omit “X=” to plot waveform)

Inputs:   x    input signal

win    window or window length in samples

inc    frame increment in samples

m    mode input:

‘z’  zero pad to fill up final frame

‘r’  reflect last few samples for final frame

‘A’  calculate window times as the centre of mass

‘E’  calculate window times as the centre of energy

Outputs:   f    enframed data – one frame per row

t    fractional time in samples at the centre of each frame

w    window function used

By default, the number of frames will be rounded down to the nearest

integer and the last few samples of x() will be ignored unless its length

is lw more than a multiple of inc. If the ‘z’ or ‘r’ options are given,

the number of frame will instead be rounded up and no samples will be ignored.

Example of frame-based processing:

INC=20                                                       % set frame increment in samples

NW=INC*2                                                     % oversample by a factor of 2 (4 is also often used)

S=cos((0:NW*7)*6*pi/NW);                                % example input signal

W=sqrt(hamming(NW),’periodic’));          % sqrt hamming window of period NW

F=enframe(S,W,INC);                       % split into frames

… process frames …

X=overlapadd(F,W,INC);               % reconstitute the time waveform (omit “X=” to plot waveform)

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