Audacity Part 1

H ng D n S D ng H ng D n S D ng Audacity 1.3.4Audacity 1.3.4

Nguyn gc: Audacity 1.3.4 Manual

Ngi dch: Nguyn nh Trung

Nguyn Cng Ngc Sn

Nguyn Hi H

M c l c

Gii thiu...................................................................................................................................3X l m thanh c bn vi Audacity.......................................................................................3

1 Hiu chnh mt tp tin c sn.......................................................................................................32Ln u th thu m trn Audacity.................................................................................................63Trn nhc nn cho bi din vn ca bn........................................................................................94Sao chp bng t, a than, minidisc ra CD.................................................................................10

Mt s iu bn cn bit.........................................................................................................121m thanh s.................................................................................................................................122D n ca Audacity.....................................................................................................................173Di v on m thanh..................................................................................................................184Vng chn....................................................................................................................................205Thit lp v cu hnh Audacity....................................................................................................21

S dng Audacity....................................................................................................................231Pht v thu m..............................................................................................................................232Thu phng....................................................................................................................................273Chn vng m thanh cn x l....................................................................................................294Chnh sa: Ct, Dn, Sao chp....................................................................................................345Hy bc v lm li nhng thao tc lm................................................................................426Nhp v Xut...............................................................................................................................447p dng hiu ng........................................................................................................................458Thay i m lng vi cng c ng bao................................................................................519Di v on m thanh..................................................................................................................5510Ho trn.....................................................................................................................................5911Di nhn.....................................................................................................................................6212Di thi gian..............................................................................................................................67

Ph lc......................................................................................................................................681Cc cu hi hay gp.....................................................................................................................682Lc nhiu trn Audacity..............................................................................................................723Cc thanh cng c ca Audacity..................................................................................................76

Gi i thi u

Gii thiuAudacity l mt chng trnh x l m thanh ph bin v pht trin nhanh nht hin nay. y l mt chng trnh hon ton min ph v l chng trnh DUY NHT chy trn nn c 3 h iu hnh ln l OS X, Linux v Windows. Audacity c dch ra hn 30 th ting khc nhau, v c mt cng ng ngi dng khp ni trn th gii. Nh , ngun t liu cho chng trnh rt di do v phong ph. Audacity c bit d dng, bn ch cn mt s kin thc nn tng v m thanh v x l m tha-nh s l c th lm quen v s dng Audacity thu a CD demo, chuyn cc bi ht mnh c t a t sang a CD, hoc hiu nh li cc tp tin m thanh trn my ca mnh ch cho vui.

Ci t Audacity trn Ubuntu

ci t Audacity trn Ubuntu, bn c th chn chng trnh t b qun l gi Synaptic hoc g dng lnh sau trn dng lnh Thit b u cui:$ sudo apt-get install audacity

Ngoi ra, ta cn c th ci t thm cc hiu ng cho Audacity:$ sudo apt-get install ubuntustudio-audio-plugins

X l m thanh c bn vi Audacity

1 Hiu chnh mt tp tin c sni vi mt ngi dng mi, cch n gin nht lm quen vi Audacity l m

v hiu chnh mt tp tin m thanh c sn. Bi hng dn ny s gip bn lm quen vi cc thao tc x l m thanh c bn nht m Audacity cung cp.

Chn mt tp tin m thanh

Audacity c th m nhiu nh dng m thanh ph bin nh WAV, AIFF hay MP3. Tuy vy, n khng m c nh dng WMA hay cc nh dng c chng sao chp.

Nu bn cn x l m thanh trn mt audio CD, bn phi trch ni dung a thnh cc tp tin m thanh (hay cn gi l rip CD). Xin xem thm phn Trch m thanh t a Audio CD.

hon tt bi thc hnh ny, bn phi c sn mt tp tin m thanh trong my. Nu cn, bn c th ln mng v ti v mt tp tin. C rt nhiu ca khc min ph trn mng, v d nh bi Stay Away From Me ca Joshua Morin. y l mt bi ht

X l m thanh c b n v i Audacity

min ph, c phn phi theo giy php Creative Commons Attribution-Sharealike tng t nh giy php GPL m Audacity tun th.

M tp tin vi Audacity

m mt tp tin trn Audacity, ta c th chn File => Open hoc ko th tp tin vo ca s chng trnh (trn Windows v Mac). i vi Linux, bn c th chy Audacity t dng lnh dng sau:

$ audacity /path/filename.mp3

Quan st dng sng

Dng sng l th trong trc tung l bin v trc honh l thi gian pht ca m thanh. C th ni, dng sng cng ln th m thanh pht/thu c s cng to v ngc li.

i vi tn hiu stereo1, dng sng ca mt di m2 s gm 2 phn, phn nm trn l ca knh tri v phn di l ca knh phi. Trn vng th dng sng cn c thc k ngang, cho bit thi gian pht ca m thanh theo pht v giy.

Nghe li tp tin

pht li tp tin va m, bn c th dng nhn nt Play trn thanh cng c iu khin hoc g du cch trn bn phm. Nu bn khng nghe thy m thanh t loa sau khi nhn nt Play, xin xem phn Thit lp v cu hnh Audacity

1 Hay lp th hoc ni - m thanh c 2 knh tri phi c lp tng ng vi 2 loa.2 track

Minh ho 1: Dng sng tn hiu m thanh

Minh ho 2: th dng sng ca m thanh stereo

Minh ho 3: Thanh cng c iu khin ca AudacityCc nt t tri sang phi:

Pause, Play, Stop, Skip to Start, Skip to End, Stop.


Nu bn chn mt vng m thanh trong d n, Audacity s pht t u n cui vng chn. Nu khng c vng no c chn, Audacity s pht t v tr con tr n cui d n. Bn c th nhn chut vo mt v tr di chuyn con tr n , hoc r chut chn mt vng m thanh cn pht li.

chn ton b m thanh trong vng th dng sng, bn nhn Ctrl+A v u tp tin, ta c th dng chut bm nt Skip to Start, hoc nhn phm

Home. v cui, bn nhn chut vo Skip to End, hoc nhn phm End.Bn c th dng cc mi tn tri phi di chuyn con tr trong khi pht.Audacity cn c nhiu cch khc iu khin vic pht li m thanh. Xin xem

thm phn Pht v Thu m.

To mt on m thanh di 10 giy

X l m thanh trn Audacity cng ging nh x l vn bn vi OpenOffice Wri-ter vy! Bn c th ct, chp, xo hay dn m thanh cng ging nh khi lm vi vn bn. Vi phn thc hnh ny, chng ta s th ct bt tp tin m thnh 1 on gii thiu di 10 giy...

Trc ht bn phi chn phn m thanh cn x l. chn chnh xc v tr ban u (10 giy), bn s cn s dng n cc lnh thu

phng nm trong trnh n View. Ta c th phng to (Zoom In), thu nh (Zoom Out) hay phng to vng chn (Fit Selection) chn ng im u ca vng cn ct b.

Sau khi t con tr ng v tr 10 giy, ta c 2 cch lm:Cch th nht, bn nhn t hp phm Shift+Home chn ton b vng m thanh

t u cho n v tr con tr, ri chn Edit => Trim (hoc nhn phm Ctrl+T) ct b nhng m thanh nm bn ngoi vng chn.

Cch th hai, bn nhn Shift +End chn ton b vng m thanh t v tr con tr v cui, ri chn Edit => Delete (hoc nhn phm Delete) xo phn m thanh va chn.

Lu rng ging nh x l vn bn, bn c th m rng (hoc co ngn) vng chn bng cch gi Shift (hoc Ctrl+Shift) v di chuyn con tr bng phm mi tn, hay phm End v Home. Bn cng c th va dng chut chn im bt u/kt thc, va gi Shift (hoc Ctrl+Shift) m rng(hoc co ngn) vng chn.

Ngoi ra, bn cn c th s dng thanh Selection Bar. Thanh ny gm 2 ghi thi gian bt u v thi gian kt thc hoc di vng chn, tu bn chn.

Nu l tay xo lm, bn c th nhn t hp Ctrl+Z quay lui, hoc chn lnh Edit => Undo bng chut. Audacity cho php bn quay lui hay lm li tt c nhng hnh ng thc thi.


Gim dn m lng trong 1 giy cui

Trong bc ny, bn s p dng hiu ng gim dn m lng cho 1 giy trc khi kt thc on m thanh 10 giy va ct ra.

Sau khi chn ng 1 giy cui cng cn gim dn m lng, bn chn Effect => Fade out p dng hiu ng cho vng chn.

Xut d n ra mt nh dng m thanh

Trong trnh n File c 2 lnh l Save v Export. Lnh Save s ghi d liu bn ang c ra a cng di dng tp tin .aup m ch c Audacity c th c. Lnh Ex-port cng ghi thng tin ra a cng, nhng cc nh dng ph thng m nhiu chng trnh khc c th c c.

Trong hp thoi Export, bn c th chn cc nh dng WAV, MP3, Ogg Vor-bis... ghi tp tin thu c ra a cng. i vi mi nh dng, Audacity cung cp cho bn mt s tu chn nht nh. Bn c th m hp thoi Tu chn cho mt nh dng bng nt Tu chn.

i vi nh dng MP3, Audacity yu cu h thng ca bn phi ci t chng trnh LAME. Bn c th ly chng trnh ny t trang ch ca Audacity, hoc dng kho phn mm:

$ sudo apt-get install liblame0

2 Ln u th thu m trn AudacityTrong bi thc hnh ny, ta s th thu m bng microphone vi Audacity.

Chn gic cm ph hp

C rt nhiu loi gic cm dnh cho thit b m thanh:


.

Bng 1.: Cc loi gic dng ni cc thit b m thanh

Chn thit b thu m cho Audacity

Chn Edit => Preferences, hp thoi Audacity Preferences xut hin. Trong phn Audio I/O, bn chn thit b thu m cho Audacity t danh sch th xung trong phn Record.

Minh ho 4: Gic mono 3 ly, t c s dng Minh ho 5: Gic mono 6 ly, dng cho n

guitar in

Minh ho 6: Gic Stereo 3 ly ca tai nghe, micro dng cho my tnh, CD, Walkman... Bn phi chuyn cc loi gic khc v loi ny cm vo card m thanh ca mnh.

Minh ho 7: Gic Stereo 6 ly, thng dng cho ampli, my tp n, microphone.

Minh ho 8: Gic RCA hay c dng trong u a CD, VCD v dn Hifi Minh ho 9: Gic XLR, hay c

dng trn ampli, bn trn v cc thit b m thanh chuyn nghip. Mt s loi micro cng dng loi gic ny.


Sau khi chn ng thit b thu m, ta cn iu chnh tn hiu thu c thng qua thanh cng c Me-ter Toolbar o mc tn hiu thu c.

Kim tra tn hiu vo

Trc khi ghi m tht, bn phi kim tra tn hiu u vo m bo tn hiu khng b ghim li do qu ln, hoc tn hiu qu b khng t c nhiu nn.

Sau khi bm chut vo thanh o u vo, bn th ni vo mic xem mc m lng thu c ph hp cha. Tn hiu khng c php to n mc lm cho ct ch th chm ti cui thang o, nhng phi ln tn hiu m thanh to hn rt nhiu so vi tn hiu nhiu, vn lun tn ti trong card m thanh, mic...

Nu tn hiu thu c qu to, bn cn iu chnh li mc m lng trong hp thoi iu khin m lng ca h thng.

Ngay c khi th vi b o, bn cng nn kim tra li bng cch ghi m tht mt vi giy v kim tra xem tn hiu c b ghim1 khng.

Thu m tht

thu m, bn nhn nt Record trn thanh cng c Control Toolbar.Audacity cn c ch Ghi m nh thi, cho php bn ch nh thi gian ghi m

v kt thc vic ghi m. Chn Track => Timer Record v ch nh thi gian bt u

1 Ghim p l hin tng in p vt qu mt mc no s b san bng, ging nh bo ha trong ha hc

Minh ho 11: Chn thit b thu m cho Audacity trong hp thoi Audacity Preferences

Minh ho 10: Bm vo thanh o tn hiu thu c


(Start Date and Time), kt thc (End Date and Time) hay di on m thanh cn ghi (Duration).

Thu gn m thanh thu v chun ho m lng

Bn chn vng m thanh cn gi li v chn lnh Edit => Trim xo b cc m thanh nm ngoi vng chn.

Tip n bn chn Effect => Normalize chun ho m lng cho m thanh thu. Hiu ng ny s xo b thnh phn mt chiu ri khuch i tn hiu in p biu din m thanh.

Lu hoc Xut tn hiu thu

Phn ny ging nh bi hng dn trc.

3 Trn nhc nn cho bi din vn ca bn

Thu m bi din vn

Bi hng dn trc ni v cch thu m bng microphone vi Audacity.Ngoi cch thu m thng thng, bn c th va nghe nhc nn va pht biu

khp ni dung ca 2 m thanh vo nhau: Chn hp kim Play existing tracks while recording new one trong th Audio I/O hp thoi Preferences hin ra khi bn chn Edit => Preferences trc khi nhn Record.

trnh nhiu do m thanh pht li thot ra loa ri vo microphone, bn nn eo tai nghe khi thc hin thao tc ny.

Nhp nhc nn vo d n ca bn

Chn File => Import v chn tp tin cn nhp. Lnh ny m tp tin v a ni dung ca n vo mt di m thanh mi.

Audacity t ng trn m thanh gia cc di m. Cc tn hiu nm trn cng mt mc thi gian tt c cc di m s c pht li cng mt lc.

Bn c th nghe ring mt di m bng cch bm nt Solo, hoc tt ting ca mt di bng cch nhn nt Mute.

Di chuyn di m thanh n v tr ph hp

Dng cng c Move Tool, bn c th di chuyn di m thanh theo trc thi gian.


iu chnh m lng gia cc di m

Bn tri mi di m u c mt bng cha tn di, cng vi 2 nt Mute, Solo v 2 thanh trt Gain v Pan. Thanh trt Gain cho php bn thay i m lng chung cho ton b di. Ko sang phi, m thanh ca di s c khuch i ln, v sang tri s lm n b i. Thanh trt Pan gip iu chnh cn bng m lng gia loa tri v phi. Ko dch con chy sang tri (ch L) s tng m lng cho loa tri v gim m lng ca loa phi, ko sang phi (ch R) th ngc li.

Gim dn nhc nn khi kt thc

Bn p dng hiu ng Fade Out ni bi trc.

Lu hoc Xut thnh qu ca bn

Phn ny ging vi bi hng dn 1.

4 Sao chp bng t, a than, minidisc ra CD

Kt ni cc thit b

Bn c th kt ni my tnh vi cc thit b bn ngoi nh cassette, u a, dn Hifi... truyn m thanh lu trong bng t, a VCD hay DVD sang cho Audacity.

Bn cn chn ng loi cp ni t gic OUT ca dn, u a.. sang cng Line-In ca my tnh. Thng thng cng Line-In ca card m thanh c mu xanh nc bin. Bn khng nn ni cc thit b vi my tnh qua ng Mic, v ng ny ch thu c m thanh mono v khng chu c m thanh ln pht bi ampli hay dn Hifi.

Thng thng, c mt dy cp c 1 u 6 ly ( cm vo ng Headphone ca thit b bn ngoi) 1 u 3 ly ( cm vo ng Line-In) ta phi dng ci chuyn gic cho 1 u cp. ng Headphone ca thit b bn ngoi thng cho php ta hiu chnh m thanh ra ca thit b, nn cm vo ng ny l d iu chnh nht. Tuy nhin nu dn m thanh c ng AUX hay Record ra, bn cng c th dng loi cp RCA kt ni ti my tnh. m lng t 2 ng ny thng l khng iu chnh c.

Lu khi kt ni mt my pht Minidisc: ng Line-out ca my Minidisc cho m thanh qu to, gy mo ting. Nu hin

tng ny xy ra, bn nn chuyn gic sang ng Headphone. a phn cc my pht Minidisc s dng cng 1 gic ra cho c ng Line-Out ln Headphone, v


ta phi chn ty chn headphone out trong phn Sound Out trn my. ng Headphone cho php bn chnh m lng u ra ca my ti card m thanh my tnh.

Thc hin

1. Chn thit b pht li v thu m trong phn Audio I/O ca hp thoi Preferen-ces (chn Edit => Preferences).

2. Nu mun thu m thanh stereo, hy chn s knh thu m l 2 (stereo).3. Chn ng Line-in lm ngun tn hiu cho Audacity.

Nu khng c ng Line-in?Mt s my Mac v laptop khng c ng Line-in. Trong trng hp , kim tra xem ng MIC c th chuyn thnh Line-in thng qua phn mm hay khng. i khi ngun Line-in cn c k hiu l MIX hay Stereo Mix, bn c th chn n trong hp thoi iu khin m lng ca h thng.Nu bn khng c ng Line-in cng nh khng th cu hnh ng MIC thnh Line-in, bn cn mua 1 card m thanh USB, hoc thit b vo/ra khc kt ni qua USB thm ng Line-in vo h thng. V d nh Griffin iMic (c 1 u vo 3 ly chun) Behringer UCA202 (u vo RCA) Nu dng thit b USB ghi m, bn chn n lm thit b ghi m trong phn Audio I/O ca hp thoi Preferences. Khi bn dng mt thit b vo ra n gin nh iMic, thanh cng c Mix s b v hiu ho. Trong iMic, bn c th cu hnh chuyn n thnh ng line-in.

4. t mc m lng ca u vo. Nhn vo mi tn bn phi (mu ) b o m lng v chn monitor input (hoc start monitoring). Pht mt on m thanh to t thit b bn ngoi v iu chnh li thanh trt trn Thanh cng c Mixer tn hiu gn t ti gii hn. Nu b o khng xut hin trong vng lm vic ca bn, hy chn hp kim Enable Meter Toolbar trong hp thoi Preferences.

5. Nu bn cn nghe m thanh ang thu, bn c th m hp iu khin m lng ri bt m thanh ng Line-in trong phn thit b pht li, v vn to m lng ln.

6. To mt d n mi bng cch chn File => Save Project As. Bt u thu m bng cch bm nt Record, v bt dn, cassette... Bn c th tm ngh gia cc bi ht trn bng t/a VCD... bng nt Pause, cho php bn ghi m 1 di duy nht trong Audacity. y l cch d lm nht, v sau bn c th chia nh di m ra nhiu bi ht khc nhau dng nhn. Xem bc 10 bit thm.Nu bn cn chuyn m thanh thu sang mt di m mi trong Audacity, hy nhn Stop, chnh li bng t n ch cn ghi m, ri lp li thao tc nhn Re-


cord v bt bng t. Audacity s ghi m thanh thu c vo mt di m mi nm di di c.

7. Nhn Stop sau khi hon tt vic thu m. Bn c th chnh sa li phn m tha-nh va ghi, nh ct b phn m thanh tha, hoc p dng mt s b lc nh Noise Removal (lc nhiu) hay Click Removal (lc ting click mi khi bt/tt bng cassete)

8. Nu va lng vi phn m thanh thu c, bn phi xut chng ra mt tp tin m thanh .WAV hay .MP3 c th pht li trn cc chng trnh khc, hoc ghi ra Audio CD. xut ton b m thanh thu ra mt tp tin duy nht, bn chn lnh File => Export. Nu mun xut ra nhiu tp tin m thanh ri rc, tng ng vi tng bi ht trong phn m thanh thu, bn cn phi nh du cc bi ht ring l trong ton b di m, bng cch chn ring vng m thanh ng vi mi bi v chn Track => Add Label at Selection v t tn cho nhn. Bn c th xut mt di m thnh nhiu tp tin n l bng cch t nhn cho mi vng cn xut v chn lnh File => Export Multiple ri chn tu chn Label trong phn Split files based on. Xin xem thm phn Chia m tha-nh thu thnh nhiu di m ring bit.

9. Cc nh dng ph bin m bn c th xut ra l .WAV, .AIFF v .MP3. .WAV v .AIFF c cht lng tng ng vi m thanh nguyn bn, nhng dng hn 10MB a cng cho mi pht m thanh. Nu bn mun ghi cc tp tin ra a CD dng vi my chi a, hy xut d n ra cc tp tin .WAV hay .AIFF vi tu chn tn s ly mu l 44100 Hz, cht lng 16 bit stereo. Xin xem thm phn Ghi a CD nh th no.

10.Nu mun tp tin m thanh ca mnh c kch thc nh hn, bn c th xut d n ra .MP3 (cht lng m thanh s km hn so vi nguyn bn). Bn cng c th ghi cc tp tin MP3 ra a CD d liu hoc CD MP3, mt a CD nh vy c th cho bn nghe nhc khong 11 ting. Lu rng bn ch c th pht loi a CD ny trn my tnh, u c CD MP3 v trn mt s u c DVD. xut tp tin .MP3, bn phi ci b m ho LAME trong h thng v cu hnh Audacity bit th vin LAME nm u. Xin xem phn Ci t LAME.

Mt s iu bn cn bit

1 m thanh s

Ly mu m thanh

M t s i u b n c n bi t

m thanh ta nghe c l nh p sut ca sng m trong khng kh. Bt u t nh bc hc Thomas Edison, nhn loi pht minh ra rt nhiu cng c lu tr sng m v sau ti to li n.

Cc thit b lu tr kiu tng t (bng cassette, a than...), biu din hnh dng sng m mt cch trc tip bng mc t ho trn on bng. Lu tr m thanh theo kiu tng t c th ti to li m thanh mt cch hon ho, nhng li gp phi cc vn v nhiu. Trong qu trnh thu v sao chp cc bng t, mc nhiu ca tn hiu ngy cng ln hn, lm tnh trung thc ca m thanh b gim xung. Do vy, theo thi gian cc tn hiu nhiu trn thit b lu tr tng t ngy mt nhiu hn. Mc d ta c th lm gim cc tn hiu nhiu xung, nhng khng bao gi c th xo b hon ton chng.

Thu m s li lm vic theo cch khc: n ly mu sng m nhng khong thi gian u n, v biu din cc mu thnh cc con s chnh xc. Thng tin trn a CD, bng m thanh s hay my tnh c nhn v cc thit b lu tr s khc khng b h hao khi sao chp nn khng lm gim cht lng ca m thanh c lu tr. Hnh di y m t mt sng m c ly mu:

Minh ho 13: Dng sng m c s ha thng qua vic ly mu tn hiu

m thanh s c th c ho trn, chnh sa m khng b nhiu thm. Hn na, nhiu hiu ng s c th c p dng ln tn hiu m thanh. Bn c th thm ting vng, m bi, tng gim mt di tn s hoc cao ca m.

Audacity l mt phn mm bin tp, chnh sa, trn v p dng cc hiu ng ln tn hiu m thanh s. Audacity c th pht hay thu m thng qua phn cng trn my bn. a s cc my tnh bn hin nay u dng card m thanh tch hp c cc gic 3 ly cm microphone hay nhng ngun m khc, cho php thu v pht li m thanh. Nhiu my tnh xch tay cn c tch hp sn c loa v microphone. Tuy nhin, nhng thit b ny thng thng cho cht lng m thanh thp. Nu bn mun c cht lng m thanh chuyn nghip, xin xem thm phn . bit cch thit lp pht v thu m vi Audacity, xin xem Thit lp v cu hnh Audacity.

Minh ho 12: Dng sng m


Cht lng m thanh s

Cht lng ca m thanh s ch yu ph thuc vo 2 nhn t: tn s ly mu v nh dng mu1. Tng tn s ly mu hoc s bit m ho mt mu s tng cht lng m thanh ghi li, nhng cng lm tng dung lng m tp tin m thanh s dng.

Tn s ly mu

Tn s ly mu (n v: Hz) l s mu c ghi li trong mt giy biu th dng sng m thanh. Tn s ly mu cng cao th dng sng m cng c m ho chnh xc hn. Tai ngi c th cm th cc sng m tn s t 20Hz n 20000Hz. Nhng m thanh nm ngoi di tn s ny gi l sng siu m v sng h m.

ghi li m thanh tn s f , ta cn phi c tn s ly mu ti thiu l 2f (gi l tn s Nyquist). Do vy, 40000Hz l tn s thp nht cn thit ly mu m thanh. a Audio CD s dng tn s 44100Hz. nhn ra ging ni, ta ch cn nghe cc tn s m thanh nm di 4000Hz, di tn s dng trong mng in thoi l 200Hz 4000Hz. Do , tn s chun ghi m ging ni l 8000Hz v c gi l m thanh cht lng ting ni.

Cc tn s ly mu chun l 8KHz, 16KHz, 22.05KHz, 44.1 kHz, 48 Khz, 96 kHz v 192 Khz. Audacity h tr tt c nhng tn s ly mu ny. Tuy nhin hu ht card m thanh trn my tnh u ch h tr ti tn s 48KHz, mt s loi cao cp c th h tr ti 96KHz. V vy, tn s ly mu 44.1 kHz vn c dng nhiu nht.

Trong hnh di y, na tri ca sng m c tn s ly mu thp v na phi c tn s ly mu cao:

Cc nh dng mu

nh dng mu, hay su bit, hay s bit m ho, l s bit c dng m ho mt mu. Cng nhiu bit c dng c ngha l bin sng m c m ho cng chnh xc hn. Tng s bit ng ngha vi vic tng phm vi ng2 ca m thu c.

Phm vi ng c o bng decibel (dB). Tai ngi nghe c m thanh c phm vi ng t nht 90dB. Tuy nhin, ngi ta lun ghi m trn phm vi ng ln hn

1 Cn gi l su bit (bit depth)2 chnh lch v bin gia m thanh nh nht v to nht c th biu din


90dB rt nhiu, ghi li nhng m thanh rt nh nhm m bo tnh trung thc khi thu m.

Cc nh dng mu chun v phm vi ng tng ng ca chng: S nguyn 8-bit: 45 dB S nguyn 16-bit: 90 dB S nguyn 24-bit: 135 dB S du phy ng 32-bit: v cngNhng nh dng mu khc, nh ADPCM xp x 16-bit m thanh bng mu 4-bit

nn. Audacity c th nhp nhiu dng khc nhau, nhng thng th chng t khi c s dng v c rt nhiu phng thc nn tt hn.

Audio CD v cc tp tin m thanh trn my tnh s dng nh dng mu s nguyn 16-bit. nh dng mu mc nh trn Audacity l dng s du phy ng 32-bit. iu ny s lm tng cht lng m thanh thu c so vi cc chng trnh ch dng nh dng mu 16-bit hay 24-bit. Bn c th cu hnh nh dng mu mc nh ca Audacity trong th Quality ca hp thoi Preferences hoc t nh dng mu cho tng di m qua trnh n th xung.

Trong hnh minh ho di y, na bn phi ca dng sng c m ha bng nhiu bit hn na tri. Bn c th hnh dung, nu tn s ly mu l khong cch gia cc ct dc th nh dng mu l khong cch gia cc ng ngang.

Minh ho 14: Na phi dng nhiu bit m ha 1 mu hn na tri

Kch thc tp tin m thanh

Cc tp tin m thanh thng c kch thc ln hn hu ht cc loi tp tin khc (tr tp tin video). tnh kch thc ca tp tin m thanh khng nn, ta nhn tn s ly mu (v d, 44100Hz) vi nh dng mu (v d 16-bit), s knh m thanh (v d m thanh stereo c 2 knh), v thi gian pht tp tin. a Audio CD dng 6 t bit m ho 74 pht m thanh stereo. Chia kt qu cho 8 ta c dung lng tnh theo byte. Mt a audio CD cha khong 800MB. Xin xem phn m thanh nn di y.

Hin tng ghim mc tn hiu


Mt hn ch ca m thanh s l cc thit b khng th m ho c cc mc m thanh ln hn mt gii hn no . Khi mt tn hiu thu c nm ngoi mc cho php, cc mu tn hiu s b ghim li gi tr ln nht m thit b c th m ho c (xem hnh).

Minh ho 15: Hin tng ghim mc tn hiu

m thanh b ghim s b bin dng (ting guitar in trong nhc rock chnh l ting b mo do hin tng ghim p). Mc d mt s k thut c th lm gim mt lng nh bin dng do ghim p gy ra, nhng ngi ta lun trnh hin tng ny khi thu m bng cch gim m lng ca ngun tn hiu (microphone, my cassette, my thu...). Trong Audacity, ta cn c th gim m lng u vo (trong thanh cng c Mixer Toolbar) sao cho dng sng m thu c ln nht c th c, nhng khng ti mc gy ra hin tng ny.

m thanh nn

V kch thc ca tp tin m thanh khng nn thng rt ln, ngi ta lun c gim tc ly mu xung m khng nh hng nhiu n cht lng ca m thanh. Nm 1991, nh dng MP31 ra i v c ph bin rng ri. MP3 l mt phng php nn mt d liu c th lm gim kch c tp tin m thanh n mc ng kinh ngc m khng nh hng nhiu n cht lng m thanh. Mi giy m thanh c cht lng CD ch mt 1.4 Mb, vi tn s bit l 128 Kbps (h s nn hn 10 ln). MP3 da trn nguyn tc b bt phn chi tit trong dng sng m m tai ngi kh phn bit.

Mc d vi mt b loa tt, ngi ta vn c th d dng phn bit s khc nhau v cht lng gia mt tp tin MP3 vi mt tp tin khng nn trn a CD, nhng vi cc thit b ph thng, iu ny rt kh phn bit. Tp tin MP3 loi 192kbps v 256-kbps c cht lng kh tt nn c s dng rng ri.

C rt nhiu cc nh dng nn mt d liu khc. Audacity h tr nh dng Ogg Vorbis tng t nh MP3 nhng hon ton m v min ph. nh dng Ogg Vorbis hin nay u vit hn hn MP3, v chng ti khuyn bn nn s dng nh dng ny lu cc tp tin ca mnh. Tuy nhin, thc t l hin nay nh dng MP3 vn c a s cc thit b lu ng v cc my iPods h tr ch khng phi l Ogg Vorbis...

1 MPEG 1, lp 3


Mt s phng thc nn ph bin khc hin nay c th k n ATRAC dng trn my thu m Sony Minidisc, WMA ca Windows Media Player v AAC.

2 D n ca AudacityTa dng Audacity m mt tp tin, thay i nhanh mt s th v lu li vo a

cng, hay trn ln nhiu di m thanh khc nhau v thm vo hng trm hiu ng to thnh 1 bi ht hon chnh... Tt c cc cng vic trn u c thc hin trn mt d n1 ca Audacity.

Mi ca s Audacity l mt d n. Mt d n c th l mt on thu m nh, mt bi ht di 3 pht hay mt a CD di 74 pht vi nhiu bi ht khc nhau bn trong. Trong d n c th c nhiu di m, on m hay nhn khc nhau nhng ch c mt trc thi gian duy nht. Audacity c th to ra v m li cc d n c lu trn a cng. Khi bn lu mt d n, gn nh mi th trong ca s d n u c lu li: tt c cc di m v cc thng tin chnh sa. Th duy nht khng c lu li l lc s history - nhng cng vic bn thc thi trong phin lm vic trc. Bn s khng th quay li nhng thao tc lm sau khi lu v m li mt d n. Tuy nhin, bt k lc no bn cng c th to mt nh chp nhanh snapshot ghi li tnh trng hin ti ca d n.

So snh gia Lu v Xut

Cc d n c lu trn a cng sao cho Audacity c th d dng m li chng. a s cc chng trnh khc khng m c cc d n ca Audacity. Khi bn mun to mt tp tin m thanh m trn cc ng dng khc, chp vo my iPod hoc ghi ra a CD, bn s cn xut ra tp tin theo chun .WAV hay .MP3. Xin xem phn nh dng tp tin m thanh bit thm. Tuy nhin, khi bn xut m thanh, bn s khng gi c thng tin ca cc di m thanh ri rc, nhn hay nhng thng tin ch c trong d n. Bn ch c th xut tp tin hon chnh ho trn ln a cng. Do , nu bn mun tip tc bin tp d n trong phin lm vic sau, hy lu d n li thay v xut ra tp tin .WAV hay .MP3.

Lu d n ca Audacity ln a cng

Thay v ch dng mt tp tin, Audacity thng dng khong 100 n 1000 tp tin, mi tp tin cha 10 giy m thanh lu mt d n. Khi bn lu mt d n, v d tn l MyRecording ch hn, Audacity s to trn a cng 2 thnh phn sau:

MyRecording.aup tp tin chnh ca d n MyRecording_data th mc cha cc tp tin m thanh nh trong d n

1 project


C 2 thnh phn ny v tt c cc tp tin bn trong th mc d liu cn phi tn ti mt d n hot ng. Nu bn cn di chuyn d n ca mnh sang th mc khc, bn phi di chuyn c 2 thnh phn ny. Nu bn cn gi mt d n sang cho ngi khc qua email ch hn, hy nn c 2 thnh phn vo mt tp tin ZIP hay RAR ri gi i.

Nu bn l tay xo tp tin m thanh chnh, hay mt vi tp tin d liu, bn s phi phc hi d n li bn trong Audacity. Xem phn d n bit thm.

S ph thuc

Khi bn m hay nhp mt tp tin m thanh khng nn, kiu .WAV hay .AIFF, Audacity s khng chp tp tin vo d n m ch tham chiu ti n tit kim thi gian x l. Tp tin gc vn khng b thay i, tr phi bn thit lp Audacity lm vy. Bn khng c thay i tp tin gc bng mt chng trnh khc khi vn lm vic vi n trn Audacity. Khi bn lu d n, Audacity s hi xem bn c cn gii quyt vn ph thuc ny khng: bn c th chp li ton b d liu t tp tin gc vo trong d n thoi mi sa hay xa tp tin gc, hoc c tip tc tham chiu ti tp tin gc mi ln m d n v bn khng ng g n n c . kim tra xem d n ca mnh c ph thuc vo tp tin bn ngoi no khng, bn chn File => Check De-pendencies...

3 Di v on m thanhMt d n ca Audacity bao gm nhiu di m1. Mi di m li bao gm cc

on2. Trong mt di m, cc on m thanh c th c di chuyn mt cch c lp, nhng c chung mt s thuc tnh ca di nh m lng, cn bng loa tri/phi, tn s ly mu v nh dng mu.

1 track2 clip


Hnh v trn th hin mt d n c 3 di m l Sax 1, Sax 2 v Drums. Di m th nht c 2 on, di th 2 khng c on no v di th 3 c 1 on m thanh. Ta c th di chuyn 1 on m thanh t di ny sang di khc bng cng c Move tool:

m thanh t mt tp tin c nhp vo hay thu t card m thanh s nm trn mt di m mi trong d n. Bn c th di chuyn, chp hay dn m thanh vo cc di m ang tn ti. chia nh mt di m thnh nhiu on, chn mt vng m thanh ri chn Edit => Split Cut.

Vi mi di m, bn c th thit lp nhiu thuc tnh thng qua trnh n th xung, hin ra khi click chut vo tiu ca di m, gn gc trn bn tri.


Cc di stereo c 2 dng sng. Dng sng nm trn l knh tri, cn nm di l knh phi (xem hnh).

Minh ho 17: Di stereo gm 2 dng sng

Hai knh m thanh trong mt di m stereo lun c chnh sa ng thi. Tuy nhin, bn c th chia chng ra v lm vic vi chng mt cch c lp bng cch m trnh n th xung ca di m (xem phn trn) v chn Split Stereo Track.

4 Vng chnTrong mt b x l vn bn, ta thng chn mt on vn bn ri chn lnh t

thanh cng c hay trnh n, v d nh ct b hay t m n. X l m thanh trong Audacity cng tng t nh vy: bn chn phn m thanh cn x l v p dng ln mt s hiu ng, thao tc chnh sa...

Vng chn ca Audacity phc tp hn so vi vng chn trong mt chng trnh son tho vn bn. Trong Audacity, vng chn gm 2 yu t l di m v thi im bt u, kt thc ca phn m thanh cn x l. Thng th bn chn cng mt lc c di m v khong thi gian cn x l bng cch nhn v r chut tri. V d, to vng chn nh trong hnh, bn bm chut thi im 5.0 giy trong di u tin v r ti thi im 7.0 giy di th hai:

Lu rng vng chn khng bao gm di m thanh th 3 nm di cng. Cc hnh ng bn thc thi s ch c p dng ln cc phn c chn trong 2 di m trn.

Ta c th thay i v tr bt u v kt thc vng chn theo trc thi gian bng cc thao tc sau:

Minh ho 16: Trnh n th xung ca di

Minh ho 18: Chn mt vng m thanh nm trn 2 di m x l.

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Audacity Part 1