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Nhn dng ting ni bng mng Nron nhn to
Ngun: Phng Ch Dng
H Th Kim Lin CH0401024 su tm gii thiu
M u
c nhiu cng trnh nghin cu v lnh vc nhn dng ting ni (Speechrecognition) trn c s l thuyt cc h thng thng minh nhn to, nhiu kt qu tr thnh sn phm thng mi nh ViaVoice, Dragon..., cc h thng bo mtthng qua nhn dng ting ni cc h quay s in thoi bng ging ni... Trinkhai nhng cng trnh nghin cu v a vo thc t ng dng vn ny l mtvic lm ht sc c ngha c bit trong giai on cng nghip ho hin i ho
hin nay ca nc nh.Mng n ron (Neuron Netwok) l mt cng c c kh nng gii quyt c nhiubi ton kh, thc t nhng nghin cu v mng n ron a ra mt cch tip cnkhc vi nhng cch tip cn truyn thng trong l thuyt nhn dng. Trongkhun kh bi bo ny tc gi mong mun c tho lun v 1 phng php nhndng ting ni s dng mng n ron vi:
- Phng php m d on tuyn tnh LPC (Linear Predictive Coding) c sdng trong vic trch trn nhng c trng c bn ca ting ni.
- Mng n ron lan truyn ngc hng (Back-propagation Neural Network) cs dng hc mu v ra quyt nh i tng nhn dng.
X l tn hiu ting ni
Qu trnh tin x l tn hiu l chuyn ting ni t dng sng (wave formrepresentation) sang dng biu din tham s (parametric form representation). Cctham s biu din tn hiu ting ni c th l: nng lng thi gian ngn (shorttime energy), t l qua im khng (zero crossing rate) t l qua mc (levelcrossing rate). c nhiu cch dng trch chn ra c nhng thng tin v
m thanh mt cch trc tip t nhng tn hiu s ca ting ni v hiu qu hn lphng php biu din tn hiu theo ph c s dng rng ri.
Phn tch ph theo phng php m d on tuyn tnh LPC c nghin cunhm trch chn ra cc c tnh c bn ca tn hiu ting ni, l nhng tham su vo cho h thng nhn dng ting ni. Phng php ny biu din mu tingni ti thi im n, x(n) bng php xp x tuyn tnh p mu qu kh:
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x(n) a1x(n - 1) + a2x(n - 2) + ...+ apx(n - p)
Trong , x(n) l mu d on ti thi im n v cc h s a 1, a2, ..., ap c coi lcc hng s trn khung (frame) phn tch ting ni.
Thm thnh phn kch thch Gu(n) th:
Trong u(n) l ngun kch thch chun ho v G l h s khuych i kchthch. Ngun kch thch chun ho em nhn t l vi h s khuych i G va vo h thng ton im cc to ra tn hiu ting ni. Mt khc, ta bit rnghm kch thch phi l xung tun hon (i vi m hu thanh) hoc l ngun nhiungu nhin (i vi m v thanh). i vi m hnh ny, ngun kch thch l mt
cng tc c iu khin bi c tnh hu thanh/v thanh ca ting ni tng ngcho php chn xung tun hon hoc nhiu ngu nhin. Mc khuch i kch thchG c nh gi trc tip t tn hiu ting ni. i vi m hnh LPC, cc tham sl s phn lp m hu thanh/m v thanh, v tr nh m tit v cc h s b lc{ak}.
Nu gi l t hp tuyn tnh ca cc mu qu kh:
th sai s tin on tuyn tnh c nh ngha:
e(n)=
Vn c bn ca phng php LPC l xc nh cc h s tin on sao cho ccc tnh ph ca b lc s trong m hnh tng hp ting ni ph hp vi dngsng ting ni trong ca s phn tch. Do c tnh bin thin theo thi gian caph tn hiu ting ni nn cc h s tin on ti thi im n phi c nh gi
trong khong thi gian ngn gn vi n. Do , cch tip cn c bn xc nhcc h s tin on l ti thiu ho sai s bnh phng tin on tuyn tnh trongmt on sng ting ni ngn. Thng thng, trong x l ting ni php phn tchph thi gian ngn c thc hin trn cc khung ting ni lin tip vi khongcch mi khung l 10 ms.
L thuyt nhn dng v mng n ron
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Nhn dng (Pattern Recognition)
C th hiu l phng php xy dng mt h thng tin hc c kh nng:cm nhn-nhn thc-nhn bit cc i tng vt l gn ging kh nng ca conngi. Nhn dng c gn cht vi 3 kh nng trn l mt lnh vc ht sc rng c
lin quan n vic x l tn hiu trong khng gian nhiu chiu, m hnh, th,ngn ng, c s d liu, phng php ra quyt nh... H thng nhn dng phi ckh nng th hin c qu trnh nhn thc ca con ngi qua cc mc:
- Mc 1- mc cm nhn: cm nhn c s tn ti cc i tng quan st, hay itng m h thng cn nhn dng. Mc ny cng a ra qu trnh thu nhn s liuqua cc b cm bin trong h thng nhn dng, v d trong h thng nhn dngting ni: i tng y l ting ni (speech) v thu nhn u vo qua Microhoc cc file m thanh .wav.
- Mc 2- mc nhn thc: y biu din qu trnh hc, m hnh ho i tng tin ti hnh thnh s phn lp (classification) cc i tng cn nhn dng.
- Mc 3- mc nhn bit: t i tng quan st c th tr li nhn bit i tng lg ? Hay y l qu trnh ra quyt nh.
Gi X l i tng nhn dng, X=(x1,x2,x3 ..., xn), ccxi R (thuc tp s)
Gi l khng gian biu din i tng:
= {X1, X2,..., Xm}
Gi l khng gian din dch, hay l tp cc tn gi ca cc lp c 1,c2,...,cn: ={w1, w2,..., wn}
Nh vy qu trnh nhn dng i tng l tm qui lut nh x t khng gian biudin sang khng gian din dch : : sao choXj Ck (i tng Xj thucvo lp Ck). Nh vy i vi h thng nhn dng, cc i tng X bit (quaquan st, cm nhn, o lng), cn khng gian din dch v qui lut l nhngiu cha bit. V bi ton y chnh l : xy dng 1 h thng t cu trc, ihi mt qu trnh hc t cc i tng quan st thu nhn c (xc nh khnggian ) n vic tm qui lut (ra quyt nh). Hnh v 1 cho ta s ca hthng nhn dng.
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Hnh 1. S tng quan ca h thng nhn dng
Mng n ron nhn to
M phng hot ng ca cc n ron thn kinh, mng n ron nhn to l h thngbao gm nhiu phn t x l n gin (neuron) hot ng song song. Tnh nngca h thng ny tu thuc vo cu trc ca h, cc trng s lin kt n ron v qutrnh tnh ton ti cc n ron n l. Mng n ron c th t d liu mu v tngqut ho da trn cc d liu mu hc.
Hnh 2: M hnh mng Neuron
Mt nhm cc n ron c t chc theo mt cch sao cho tt c chng u nhncng mt vector vo X x l ti cng mt thi im. Vic sn sinh ra tn hiu raca mng xut hin cng mt lc. V mi n ron c mt tp trng s khc nhaunn c bao nhiu n ron s sn sinh ra by nhiu tn hiu ra khc nhau. Mt nhmcc n ron nh vy c gi l mt lp mng. Chng ta c th kt hp nhiu lpmng to ra mt mng c nhiu lp, lp nhn tn hiu u vo (vector tn hiu vox) c gi l lp vo (input layer). Trn thc t chng thc hin nh mt b mcha tn hiu u vo. Cc tn hiu u ra ca mng c sn sinh ra t lp ra camng (output layer). Bt k lp no nm gia 2 lp mng trn c goi l lp n
(hidden layer) v n l thnh phn ni ti ca mng v khng c tip xc no vimi trng bn ngoi. S lng lp n c th t 0 n vi lp. M hnh n ronnhn to i hi 3 thnh phn c bn sau:
- Tp trng s lin kt c trng cho cc khp thn kinh.
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- B cng (Sum) thc hin php tnh tng cc tch tn hiu vo vi trng s linkt tng ng
- Hm kch hot (squashing function) hay hm chuyn (transfer function) thchin gii hn u vo ca neuron.
Trong m hnh n ron nhn to mi n ron c ni vi cc n ron khc v nhnc tn hiu xi t chng vi cc trng s w i. Tng thng tin vo c trng s l:Net = wjxj.
Nhn dng ting ni bng mng n ron
Hnh 3 trnh by nhng chc nng c bn ca h thng nhn dng ting ni, trong c nhng chc nng con ca tng khi. n gin trong vic ci t v yucu ti nguyn my tnh va phi ta thng nht trong cc mu s dng 8bit cho 1
mu, tn s ly mu 22025 Hzs, m thanh mono.
Hnh 3. S khi m t h thng nhn dng ting ni
Phn tch tn hiu ting ni
Phn tch tn hiu ting ni bng phng php LPC c thc hin qua cc bc
sau:- Ci thin tn hiu (preemphasis):Tn hiu ting ni s(n) c a qua h thng sbc thp (chng hn nh b lc FIR bc thp) lm phng ph vi iu kin hthng ny hoc l n nh hoc l thch nghi chm.
- Ct khung (frame blocking) : Tn hiu ting ni sau khi ci thin c chiathnh L khung - N mu, cc mu k cn c phn tch bi M mu.
- Ca s (windows): c a qua hm ca s ti thiu ho s im gin onti cc v tr bt u v kt thc khung.
- Phn tch t tng quan: cc khung c phn tch t tng quan, kt qu tac gi tr tng quan cao nht v c gi l bc phn tch LPC. Thng thngnhn gi tr t 8 n 16.
- Phn tch LPC: s dng thut ton Durbin chuyn i cc h s t tng quanthnh tp tham s LPC .
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- Chuyn i tham s LPC thnh h s phn tch ph. Trong thc nghim ta chn12 h s cepstral lm c trng ca tn hiu.
M t mng n ron trong nhn dng
- Phng n la chn s nt ca tng lp trong mng: theo kinh nghim ca ccchuyn gia v mng n ron trong cc bi ton phn lp c s dng mng lantruyn ngc hng, s dng 1 lp tnh ton l lp mng Kohonen lm lp n. Taxc nh s n ron cho tng lp.
+ S n ron lp vo = s chiu ca vector vo, y ta chn 12 h s cepstral lc trng ca mu, mi mu c x l trong L khung ting ni, th s n ron calp vo s l 12*L, v d s dng 5 frames/mu th s n ron lp vo l 60
+ S n ron lp Kohonen = s gi tr cc tp tr li. V d cn nhn dng 10 t
mi t c m t bi vector vo 60 thnh phn, ti lp n cn lu tr li gii l600, cn s n ron lp n l 625 n ron (ma trn n ron kch thc 25x25)
+ S n ron lp ra = s lng kt qu u ra, s dng phng php m ho bngs bit biu din s lng kt qu, v d cn nhn dng 128 t cn 7 n ron lpra, 7 n ron ny cho php m ho 27 = 128 gi tr
- Phng php hc cnh tranh ca lp n v qu trnh hc c ch o ti lp ra camng theo cc bc sau:
+ Khi to trng s: cc thnh phn ma trn trng s c khi to bi gi tr
ngu nhin
+ c tn hiu vo cho mng: d liu trong file mu cha thng tin mu hc vcho kt qu gm 2 thnh phn: mng 1 chiu cha vector tn hiu vo v mng 2chiu cha ma trn trng s lin kt ban u ca lp Kohonen
+ Hiu chnh ma trn trng s lp Kohonen: hiu chnh trng s lin kt n ronlp n Kohonen sao cho mng c th hc mu tt nht. T mng mt chiu chavector tn hiu vo, mng hai chiu cha ma trn trng s lin kt lp n v cchng s hc amin, amax, tmax chc nng ny phi xc nh mng hai chiu cha
ma trn trng s lin kt lp n theo cng thc:
HidWeight =HidWeight + rate(t)topo(Winner, i)(InVec(j) - HidWeight
+ Hiu chnh ma trn trng s lp ra: hiu chnh trng s lin kt n ron lp ra to bng tra cu. T mng mt chiu cha vector tn hiu ra v mng hai chiucha ma trn trng s lin kt lp ra chc nng ny phi xc nh mng hai chiu
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cha ma trn trng s lin kt lp ra bng cch hiu chnh ma trn trng s lin kt
lp ra theo cng thc: OutWeight =OutVec(k).
Phng php nhn dng
- u vo: file wave cha d liu tn hiu ting ni cn nhn dng v file dat chathng tin trng s lin kt n ron lp n v lp ra. Ngoi ra u vo ngun mcng c th l t micro thng qua sound card lm, lc ny d liu ting nic c trong buffer d liu ca Windows.
- u ra: kt qu cn nhn dng
- Qu trnh nhn dng ting ni c thc hin qua cc bc:
+ c tn hiu vo: c d liu t file wav hoc t buffer d liu m thanh
+ X l tn hiu ging nh chc nng phn tch LPC trn
+ c ma trn trng s lin kt lp n v lp ra ca mng
+ Xc nh n ron trung tm
+ Tra cu kt qu: tra cu trn bn topo mng n ron a ra gi tr cn nhndng.
Kt lunTrn y l 1 nghin cu v th nghim s dng phng php m d on tuyntnh phn tch tn hiu, s dng mng n ron lan truyn ngc hng vi lpmng t t chc Kohonen tch lu tri thc cho mng, lm c s cho vic nhndng ting ni bng cch tra cu topo mng a ra kt lun v ting ni cnnhn dng a vo h thng. Thc t h thng th nghim c th nhn dng c1 s nguyn m ting vit. Phng php LPC c p dng kh rng ri trong xl ting ni bi n cung cp m hnh l tng cho tn hiu ting ni. Hn na,LPC tng i n gin, d thc hin c bng phn cng ln phn mm m vnm bo chnh xc. Tuy nhin nhc im ca phng php ny l khng gii
quyt c vn cc tnh cht ng ca thanh mn, lm gim hiu nng ca hthng nhn dng, c bit l cc h thng c lp ngi ni.
xut hng pht trin:
nng cao hiu sut nhn dng ca h thng, theo s pht trin ca tin hc hini, hng nghin cu ny c th tip tc m rng pht trin theo cc hng sau:
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- xut mng n ron m: pht trin theo 3 hng l
+ Mng n ron vi cc u vo, trng s m
+ Mng n ron dng xc nh hm thuc
+ Suy din m vi mng neuron.
- xut dng gii thut di truyn ti u ho cu trc mng neuron. Nhnghng pht trin tip theo c nh gi theo ng m hnh v cc h thng thngminh lai, l: Hybrid Intelegent System = Neural nerworks + Expert System +Genetic Algorithms + Fuzzy Logich.
- xut cc phng php x l tn hiu s khc, c c s ci tin h thngnng cao cht lng nhn dng ca h thng. xut cc hng dng m hnh
Makov n, s dng phng php lng t ho vector b xung vo h thng./.