§Ú̦b«e¤@³¹¤¤¡A¤w¸g»¡©ú¤F¤@Ó LTI ¨t²ÎªºÀW²vÅTÀ³¡A¤]´N¬O¨ä³æ¦ì¯ß½ÄÅTÀ³ªºÂ÷´²®É¶¡³Å¥ß¸Âà´«¡A¥i¥Î¨Óªí¥Ü¹ï©ó¯S©wÀW²v©¶ªi©Ò²£¥Íªº¾_´T©M¬Û¨¤§ïÅÜ¡C¦¹¥~¡A¹ï©ó¥ô·NªºÂ÷´²®É¶¡°T¸¹ x[n]¡A¨ä¡uÂ÷´²®É¶¡³Å¥ß¸Âà´«¡v¡]²ºÙ DTFT¡^¤Î¨ä¤ÏÂà´«¥i¥Hªí¥Ü¦p¤U¡G
¥Ñ¤Wzªº²Ä¤@Ó¦¡¤l§Y¥i±À¾É¥X²Ä¤GÓ¦¡¤l¡C¦b²Ä¤GÓ¦¡¤l¤¤¡A¥Ñ©ó X(ejw) ªº¶g´Á©Ê¬O 2p¡A¦]¦¹¿n¤À°Ï¶¡¥i¥H¬O¥ô¦óªø«×¬° 2p ªº°Ï¶¡¡C
X(ejw) = Ske-jwk x[k] x[n] = (2p)-1¡ì2pX(ejw)ejwn dw ¥Ñ²Ä¤GÓ¦¡¤l¡A¥i¥H§ÚÌ¥i¥H±N x[n] ©î¸Ñ¦¨µL½aÓ°ò¥»¨ç¼Æ ejwn ªº½u©Ê²Õ¦X¡A¦Ó¨C¤@Ó°ò¥»¨ç¼Æªº¾_´T«h¬O¥Ñ X(ejw) ¨Ó±±¨î¡C´«¥y¸Ü»¡¡AX(ejw) §Y¥Nªí x[n] ¦b³sÄòÀW²v w ªº¤À¶q¡A¥i¥H¶i¤@¨B»¡©ú¦p¤U¡C
¥Ñ°ò¥»·L¿n¤À¥iª¾¡A¹ï©ó¤@Ó¨ç¼Æ f(x) ªº¿n¤À¡A§ÚÌ¥i¥H¨Ï¥Î²Ö¥[¨Ó¹Gªñ¡G
¦]¦¹¦pªG x[n] ¬O¹ê¼Æ¡A§ÚÌ´N¥i¥H±N¨ä©î¸Ñ¶}¨Ó¡Aªí¥Ü¦p¤U¡G
¡ì02p f(x) dx = limN¡÷¡ÛSk=0N-1 f(k¡E(2p/N))¡E(2p/N) ´«¥y¸Ü»¡¡Ax[n] ¤w¸g³Q©î¸Ñ¦¨ N Ó¾l©¶¨ç¼Æªº½u©Ê²Õ¦X¡A¦Ó³o¨Ç¾l©¶¨ç¼Æªº¨¤ÀW²v¬O±q 0 ¨ì 2p(N-1)/N¡A¾_´T«h¬O |X(ejw)|/N ¦b¨CÓ¨¤ÀW²vªºÈ¡C¡]¦pªG x[n] ¬O½Æ¼Æ¡A§Ṳ́]¥i¥H¶i¦æ¦¹ºØ©î¸Ñ¡A¥u¤£¹Lª«²z·N¸q¸û¤£©úÅã¡C¡^
x[n] = Re{(2p)-1¡ì2pX(ejw)ejwn dw} = (2p)-1¡ì2p Re{X(ejw)ejwn} dw = (2p)-1¡ì2p |X(ejw)| cos(wn + q) dw, q=¡çX(ejw) = N-1 Sk=0N-1 [|X(ejw)| cos(wn + q)]w=2pk/N dw, N¡÷¡Û ¥Ñ¤W¤@¸`¤Î¥»¸`ªº°Q½×¡A§ÚÌ´N¥i¥HÁA¸Ñ¡ADTFT ¨ã¦³¨âÓ«D±`«nªº·N¸q¡G
- ¦pªG h[n] ¬O¤@Ó LTI ¨t²Îªº¯ß½ÄÅTÀ³¡]Impulse Response¡^¡A¨º»ò H(ejw)
= Skh[k]e-jwk ´N¥i¥H¥Nªí¦¹¨t²Î¹ï©ó¨¤ÀW²vµ¥©ó w ªº°T¸¹©Ò³y¦¨ªº¼W¯q |H(ejw)| ©M¬Û¦ì ¡çH(ejw)¡C - ¦pªG°T¸¹ x[n] ¬O¤@Ó¥ô·N°T¸¹¡A¨º»ò X(ejw)
= Skx[k]e-jwk ´N¥i¥H¥Nªí¦¹°T¸¹¦b¤£¦P¨¤ÀW²v w ªº¤À¶q¤j¤p |H(ejw)| ©M¬Û¦ì ¡çH(ejw)¡C ¥H¤U¦C¥XÂ÷´²®É¶¡³Å¥ß¸Âà´«ªº¤@¨Ç±`¥Î¨ìªº«n©Ê½è¡C
¦pªG x[n] ¬O¤@Ó¹ê¼Æ§Ç¦C¡A¨º»ò§ÚÌ¥i¥H±N¹ïÀ³ªº DTFT X(ejw) ©î¸Ñ¦¨¹ê³¡©Mµê³¡ªº²Õ¦X¡A¦p¤U¡G
- ½u©Ê©Ê½è¡G
z[n] = a x[n] + b y[n] ¡ö¡÷ Z(ejw) = a X(ejw) + b Y(ejw) - ¶g´Á©Ê¡G
X(ej(w + 2 k p)) = X(ejw) ´«¥y¸Ü»¡¡ADTFT ªº¶g´Á¬° 2p¡C- ©µ¿ð©Ê½è¡G
y[n] = x[n-k] ¡ö¡÷ Y(ejw) = ejwk X(ejw) - ±Û¿n¡G
y[n] = x[n]*h[n] ¡ö¡÷ Z(ejw) = X(ejw)Y(ejw) ¤]´N¬O»¡¡A¦b®É°ìªº±Û¿nµ¥©ó¦bÀW°ìªº¼¿n¡C¨ä¤¤
X(ejw) = Ske-jwk x[k] = Skx[k] cos(wk) - j Skx[k] sin(wk) = XR(ejw) + j XR(ejw) XR(ejw) = Skx[k] cos(wk) ³o¨Ç¨ç¼Æº¡¨¬¤U¦C©Ê½è¡G
XI(ejw) = - Skx[k] sin(wk)
- ¦@³m¹ïºÙ¡GX*(ejw) = X(e-jw)
- XR(ejw) ¬O°¸¨ç¼Æ
- XI(ejw) ¬O©_¨ç¼Æ
- |X(ejw)| ¬O°¸¨ç¼Æ
- ¡çX(ejw) ¬O©_¨ç¼Æ
Audio Signal Processing and Recognition (µ°T³B²z»P¿ëÃÑ)