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TI : CC CHUN NN AUDIO

PCM- LPC-GSM

GING VIN HD: TRN BCH THO

NHM : 17TIN 3A1

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NI DUNG1.Tng quan nn Audio

2.Phng php nn PCM

3.Phng php nn LPC

4.Phng php nn GSM5.Ktlun

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1. cimca m thanh s:a, Sha ting ni thoi:

+ Giihngiiph: 4 KHz

+ Tnslymufs = 8 KHz, Te =125s+ Lngtha gi tr: m ha bng 8 bits+ Tc cn thit: 8000 x 8 = 64000 bits/s

(64Kb/s)

+ Cc chun nn GSM: 15.2 Kbit/s, ADPCM: 32Kbit/sb, Audio Hi-Fi (CD):

+ Giihngiiph: 4 KHz

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Cc phng php cbn m ha ting ni

1, Pulse Code Modulation - PCM = G.711: Lphng php m ha cbn, m ha trctip tn hiu

lymuting ni, m thanh vi cc lutlngtha

-law v a-law.

+ a-law: lymtmu m thanh 13 bit c du (sign)

v bini thnh mt gi tr 8 bit

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Mu vo tuyn tnh M c nn

s0000000wxyza... s000wxyz

s0000001wxyza... s001wxyz

s000001wxyzab.. s010wxyz

s00001wxyzabc... s011wxyz

s0001wxyzabcd... s100wxyz

s001wxyzabcde... s101wxyz

s01wxyzabcdef... S110wxyz

s1wxyzabcdefg... s111wxyz

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Trong sl bit du (sign bit).

Du. th hin cc bit c mc u tin thp khng

c m ha.

Vd:

1000'0000'1010'1111 c m ha thnh 1000'1010

0000'0001'1010'1111 c m ha thnh0001'1010

+ -law: lymtmu m thanh 14 bit c du (sign)

v bini thnh mt gi tr 8 bit

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Mu vo tuyn tnh M c nn

s00000001wxyza... s000wxyz

s0000001wxyzab... s001wxyz

s000001wxyzabc... s010wxyz

s00001wxyzabcd... s011wxyzs0001wxyzabcde... s100wxyz

s001wxyzabcdef... s101wxyz

s01wxyzabcdefg... s110wxyz

s1wxyzabcdefgh... s111wxyz

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3, M ha dontuyn tnh- Linear Prediction

Coding- LPC:

LPC l mt cng ccsdnghuht trong xl

tn hiu m thanh v x l ting ni biu din

ng bao ph ca tn hiu s ca ting ni trong

dng nn sdng thng tin camt m hnh don

tuyn tnh.

LPC l mt trong cc k thut phn tch ting ni

mnhm v l mt cng chiuqu cho vic m ha

ting ni chtlng cao vitc bit thp.

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M hnh LPC da trn vicxp x ton hcvgingni ca con ngi. Tithiim tmuting ni s(t)

cbiudinnhl mttngcapmutrc.Trong LPC b lcdbo tuyn tnh cho php gi tr

camutip theo sc xc nhbngskthp

ca cc mutrc.Trong iukin bnh thng cc muclyvitns8000 mu,mimtmucbiudinbng 8 bittcs l 64000bit (64 Kbit). LPC sgimtcny xung cn 24000 bit/s s dn nhintngmt mt thng tin, tuy nhin chng ta vn c thnghe v hiuc

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4.M ha GSM

Codec ny sdng chun m ha RPE-LPC (Regular

Pulse Excited Linear Predictive Coder ). y l loi

codec m ha ting ni u tin csdng trongGSM .Chun m ha ting ni ny da trn LPC kch

xung uvidon di.Nguyn tccbnda trn

2 codec : RELP (Residual Excited Linear) v MPE-

LPC(Multi Pulse Excited LPC)

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Chun nn GSM 06.10 l chun m ha ting ni c

mt mt do da trn s m ha Kch thch don

di xung u (RPE-LTP).

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*B m ha chun nn GSM 06.10

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Cc khung tn hiu ting ni u vo bao gm 160

mu tn hiu (theo mu PCM 13 bit) u tin sc

tinx l toitng tn hiux l cho b lc lm

r nt trc. 160 mu tn hiutcsc phn

tch xc nh cc tham s cho b lc phn tch

ngnhn (LPC analysis).

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Cc thng sny csdnglc chnh 160 mu

tn hiu .Ktqu ta s c c 160 mu tn hiud

ngnhn. Cc thng scacablc,hsphnxtihnscchuynn LAR (log area ratios) trc

khi ctruyni.Khung tn hiu sc phn tch

thnh 4 khung con vi 40 mu trong mi khung.Mikhung con scxl theo tng blockbi cc thnh

phnchcnngnitip sau

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- Trc khi x l tngkhinhca 40 mu tn hiungnhn, cc thng scablc phn tch di hn

: tr LTP v t LTP scc lng v cpnht

trong b phn tch LTP da trn cscakhihinti v dy 120 mu tn hiungnhntrcc

lutr

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- Mt block 40 tn hiu di hn sc to ra bng

vic tr40 mu tn hiungnhn cho chnh 40 clng ca chng. Cc blocks t c s c a

vo b phn tch kch xung uthchin qu trnh

nn cbncathut ton.

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- Ktqu sau qu trnh phn tch RPE, block 40 mutn hiu di hncbiudinbi 4 chui con mi

chuigm 13 xung.Schnlc sau c xc nh

biv tr RPE li. 13 xung RPE sc m ha sdng APCM vic lng bin block con thng

scngscchuynnbgii m. Thng sRPE

cng c chuyn ti b gii m RPE cc b vmodule ti to to ra 40 mu tn hiu di hn

clngtha.

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- Bngviccng 40 mu tn hiu di hnlngtha vo block cc c lng tn hiungnhn trc

, ta s c cc tn hiu ngn hn c xy dng

li.Cc tn hiu ny sau ca vo b lc phntch di hnto 40 clng tn hiungnhns

csdng cho block con tip theo v tiptc vng

lp

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*B gii mi ca chun nn GSM 06.10

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2. Chun nn GSM 06.20:Chun GSM cho php tch mt knh thoin thnh

hai knh thoi con c th duy tr cc cuc gi ring

bit.Vi cch chia ny cc tngimng c thnhnislng cc cucgi c thcthchin trong

mngvimt chi phutnh.

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a)Cng nghsdng trong chun nn GSM 06.20Chun codec GSM 06.20 s dng code thut ton

VSELP.Thut ton VSELP sdng cng ngh m ha

phn tch-bng-tnghp,n thuc lp cng ngh mha ting ni CELP (M ha don tuyn tnh kch

thch).

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Cc c tnh kthut:

Tnslymu:Bit rate: B = 5.6 kbps

Chtlng: - thp hn mt cht so vi chun nn

GSM 06.10- khng ph hp cho tn hiu modem v tn hiu m

nhc

ng dng: - cc h thng thng tin di ng theochun GSM (knh half-rate vi B=11.4 kbps cho m

ha knh thoi)

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- phin bn sa i vi B= 6.9 kbps trong cc hthng di ngcaNht (JDC) v vi B= 7.95 trong h

thng thng tin di ngcaM(digital AMPS)

Thut ton: -VSELP (Vector Sum Excited LinearPrediction)

- rng khung T = 20 ms , rng sub-frame =

1/4T= 5 ms- b lc LPC theo thtvi n=10 , lngtha ca

cc tham sphnx vi ba vectow lngt3 chiu,

gim phc tp bng vic s dng tin-lng t

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- d on di hn vi s kt hp tm kim vngng/vng m

- lng t ha vect ca cc yu t thu c

- b lc thch nghi nh gi li- tr tn hiu thut ton : 20ms

- phc tpkhong 18.5 MOPS (Mega Operations

Per Second)

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3. Chun nn GSM 06.60Vi spht trin ca cng ngh DSP gip hin thc

ha chun nn GSM 06.20, n cng cho php vic

pht trinmtthut ton m ha codec citinvi bitrate 13kbps cgi l chun nn GSM 06.60

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a) B m ha v gii GSM 06.60

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B gii m codec

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b) Bng thng s chun nn GSM 06.60

Ly mu Chu kBit rate B = 13 kbit/s (bao gm 0.78 kbit/s cho cc bit tng ng) Cht lng - cht lng cao hn ng k so vi chun nn 06.10 , c th so snh vi

32 kbit/s ADPCM- khng ph hp cho tn hiu modem v m nhc

ng dng - cc h thng thng tin di ng theo chun GSMThut ton - m ha CELP vi codebook i s ging vi codec theo chun GSM

G.729- rng khung = 20 ms , 4 khung con - nh r 10 h s LP 2 ln cho mi khung , lng t ha dng ma trnvecto vi phn s dng 20 h s LSF- codebook thch nghi s dng kt hp tm kim open-loop/closed-loop vp dng xc nh khong phn on bng php ni suy vi h s 6

- lng t ha d on trc cc tham s gia lng -b lc sai khc c trng s thch nghi- tr tn hiu i s 20 ms- phc tp vo khong 15.2 wMOPS (triu php tnh trn mi giy)

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4.Chun nn GSM 06.90

Chun nn GSM 06.90 l mt bng sng ch cachng trnh nn dliu m thanh tiu cho m ha

ting ni.GSM 06.90 c thng qua l cc codec

ni tiu chunca 3GPP vo thng Minm 1998 vhinangc dng rng ri trong cc mng GSM v

UMTS.

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B m ha v gii m GSM 06.90

Chun nn GSM 06.90 sdng tm codec m ngunvi bit-rate l 12,2, 10,2, 7,95, 7,40, 6,70, 5,90, 5,15

v 4,75 kbit / s. codec ny c da trn cc m

tuyn tnh kch thch m hnh dbo m ha (CELP).Mt trt t tuyn tnh 10 d on (LP), hoc ngn

hn, tng hp, b lc c s dng. Vic tng hp

cao lc c thc hin bng cch s dng ccphng php tip cn codebook ci calledadaptive.

5 Kt l

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5.Kt lun

- Vi s pht trin mnh ca cng ngh ch to phncngxl tn hiusni chung v xl tn hiuting ni

ni ring cng t c rt nhiu thnh tu, gip cho

thchinc cc thut ton tinh vi phctp

- Vit nam lnhvcxl tn hiuting ni gnymi

c ch , thng 7-2001 phnmmnhndngtingvit

c gii thiu bi vin cng ngh thng tin, v cc

phng thc phn tch tnghp ting ni bng formant

cngcgiithiubi tc gi L Hng Minh (tp ch

bu chnh vin thng thng 3-2002).

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-Tuy chng khng phi l cc snphm m ho tcthp nhng n cng l kt qu ca s phn tch

nghin cubncht ngn ngtingVit. V vy cng

tc nghin cu tingvitcnc trin khai vi ccvnnhxy dngc tnh thng k cho tingvit,

xy dngs m chun cho tingvit v tip l sn

xut cc snphm m ho tcthp choVit nam.Ta c th t tin m ngh rng cc snphm m ho

tc thp cho Vit nam s c ra i trong thi

gian khng xa.

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