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Rectangular mask short-time Fourier transform : ウィキペディア英語版
Rectangular mask short-time Fourier transform

In mathematics, a rectangular mask short-time Fourier transform has the simple form of short-time Fourier transform. Other types of the STFT may require more computation time than the rec-STFT.
Define its mask function
: w(t) =\begin
\ 1; & |t|\leq B \\
\ 0; & |t|>B
\end
We can change ''B'' for different signal.
Rec-STFT
: X(t,f)=\int_^ x(\tau) e^ \, d\tau
Inverse form
: x(t)=\int_^\infty X(t_1,f)e^ \, df\text t-B
==Property==
Rec-STFT has similar properties with Fourier transform
* Integration
(a)
: \int_^\infty X(t, f)\, df = \int_^ x(\tau)\int_^\infty e^\, df \, d\tau = \int_^ x(\tau)\delta(\tau) \, d\tau=\begin
\ x(0); & |t|< B \\
\ 0; & \text
\end
(b)
: \int_^\infty X(t, f)e^ \,df =\begin
\ x(v); & v-B\ 0; & \text
\end
*Shifting property(shift along x-axis)
:: \int_^ x(\tau+\tau_0) e^\, d\tau = X(t+\tau_0,f)e^
*Modulation property (shift along ''y''-axis)
:\int_^ (e^ ) d\tau = X(t,f-f_0)
*special input
#When x(t)=\delta(t), X(t,f)=\begin
\ 1; & |t|< B \\
\ 0; & \text
\end
#When x(t)=1,X(t,f)=2B\operatorname(2Bf)e^
*Linearity property
If h(t)=\alpha x(t)+\beta y(t) \,, H(t,f), X(t,f),and Y(t,f) \,are their rec-STFTs, then
: H(t,f)=\alpha X(t,f)+\beta Y(t,f) .
* Power integration property
:: \int_^\infty |X(t, f)|^2\, df = \int_^ |x(\tau)|^2\,d\tau
:: \int_^\infty \int_^\infty |X(t, f)|^2\,df\,dt = 2B \int_^\infty |x(\tau)|^2\,d\tau
* Energy sum property(Parseval's theorem)
:: \int_^\infty X(t,f)Y^
*(t,f)\,df = \int_^ x(\tau)y^
*(\tau)\,d\tau
:: \int_^\infty \int_^X(t,f)Y^
*(t,f)\,df\,dt =2B \int_^\infty x(\tau)y^
*(\tau)\,d\tau

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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