PCM (pulse code modulation) piav qhia txog cov txheej txheem uas hloov cov suab analog (sawv cev los ntawm waveforms) rau hauv cov cim suab digital (sawv cev los ntawm ib qho thiab xoom) uas tsis muaj qhov compression. Cov txheej txheem no tso cai rau cov ntaubntawv povthawj siv suab paj nruag, yeeb yaj kiab suab paj nruag, lossis lwm yam suab rau hauv qhov chaw me me, zoo thiab lub cev.
Kom tau txais lub tswv yim pom ntawm qhov chaw uas analog thiab digital audio coj mus, piv qhov loj ntawm cov ntaub ntawv yas (analog) rau ntawm CD (digital).
PCM Basics
PCM analog-rau-digital audio hloov dua siab tshiab tuaj yeem nyuaj, nyob ntawm cov ntsiab lus tau hloov dua siab tshiab, qhov xav tau zoo, thiab cov ntaub ntawv khaws cia, hloov pauv, thiab faib li cas.
Hauv cov ntsiab lus tseem ceeb, PCM cov ntaub ntawv suab yog kev txhais lus digital ntawm lub suab nrov analog. Lub hom phiaj yog kom rov ua dua cov khoom ntawm lub teeb liab analog kom ze li sai tau.
Kev hloov pauv ntawm Analog-rau-PCM tau ua tiav los ntawm cov txheej txheem hu ua sampling. Analog suab txav nyob rau hauv nthwv dej, tsis zoo li PCM, uas yog ib tug series ntawm ones thiab zeros. Txhawm rau ntes cov suab analog siv PCM, cov ntsiab lus tshwj xeeb ntawm lub suab nthwv dej los ntawm lub microphone lossis lwm lub suab analog yuav tsum tau coj mus kuaj.
Tus nqi ntawm cov qauv sib piv uas tau ua piv txwv ntawm ib qho chaw muab (xa mus rau cov khoom) kuj yog ib feem ntawm cov txheej txheem. Cov ntsiab lus piv txwv ntxiv nrog rau cov ntu loj ntawm lub suab nthwv dej ua piv txwv ntawm txhua lub ntsiab lus txhais tau tias qhov tseeb ntau dua tau tshwm sim ntawm qhov kawg mloog.
Piv txwv li, hauv CD suab, ib qho kev sib piv waveform yog sampled 44.1 txhiab zaus ib ob (los yog 44.1 kHz), nrog rau cov ntsiab lus uas yog 16 me me (ntsis qhov tob). Hauv lwm lo lus, tus qauv suab digital rau CD suab yog 44.1 kHz / 16 khoom.
PCM Suab thiab Tsev Theatre
PCM yog siv hauv CD, DVD, Blu-duab tshav, thiab lwm yam kev siv suab digital. Thaum siv nyob rau hauv ib puag ncig-suab daim ntawv thov, nws feem ntau hu ua linear pulse code modulation (LPCM).
A CD, DVD, lossis Blu-ray Disc player nyeem PCM lossis LPCM teeb liab tawm ntawm lub disc thiab tuaj yeem hloov mus rau ob txoj hauv kev:
- Los ntawm khaws cov teeb liab daim ntawv digital thiab xa mus rau lub tsev ua yeeb yaj kiab txais los ntawm digital optical, digital coaxial, lossis HDMI txuas. Lub tsev ua yeeb yam hauv tsev tom qab ntawd hloov lub PCM teeb liab mus rau analog kom tus txais tau tuaj yeem xa cov teeb liab los ntawm lub amplifiers thiab mus rau cov neeg hais lus. PCM teeb liab yuav tsum tau hloov mus rau analog vim hais tias tib neeg pob ntseg hnov cov suab analogs.
- Los ntawm kev hloov pauv PCM teeb liab rov qab mus rau hauv daim ntawv analog, thiab tom qab ntawd xa cov teeb liab rov tsim analog rau lub tsev ua yeeb yam lossis lub tso suab receiver ntawm tus qauv analog suab sib txuas. Nyob rau hauv rooj plaub no, lub tso suab los yog lub tsev ua yeeb yam receiver tsis tas yuav ua ib qho kev hloov dua siab tshiab rau koj kom hnov lub suab.
Feem ntau CD cov neeg ua si tsuas yog muab cov kev sib txuas ntawm lub suab sib txuas, yog li PCM teeb liab ntawm lub disc yuav tsum tau hloov mus rau analog los ntawm cov neeg ua si sab hauv. Txawm li cas los xij, qee cov CD player (nrog rau yuav luag txhua DVD thiab Blu-duab tshav Disc players) tuaj yeem hloov PCM suab teeb liab ncaj qha, siv cov kev kho qhov muag lossis digital coaxial kev xaiv.
Ntxiv rau, feem ntau DVD thiab Blu-duab tshav Disc players tuaj yeem hloov PCM teeb liab ntawm kev sib txuas HDMI. Tshawb xyuas koj tus neeg ua si thiab lub tso suab lossis lub tsev ua yeeb yam hauv tsev rau koj txoj kev xaiv kev sib txuas.
PCM, Dolby, thiab DTS
Lwm qhov ua kom yuam kev uas feem ntau DVD thiab Blu-duab tshav Disc players tuaj yeem ua tau yog nyeem cov cim tsis tau sau Dolby Digital lossis DTS suab. Dolby thiab DTS yog digital audio formats uas siv coding los compress cov ntaub ntawv kom nws haum rau tag nrho cov ib puag ncig-suab suab ntaub ntawv digitally mus rau ib tug DVD los yog Blu-duab tshav Disc. Feem ntau, un-decoded Dolby Digital thiab DTS cov ntaub ntawv suab raug xa mus rau lub tsev ua yeeb yam txais tos rau kev txiav txim siab ntxiv rau analog, tab sis muaj lwm txoj kev xaiv.
Thaum lawv nyeem cov teeb liab tawm ntawm lub disc, ntau DVD lossis Blu-duab tshav Disc players kuj tuaj yeem hloov Dolby Digital thiab DTS cov cim rau PCM uas tsis muaj kev sib txuas, thiab tom qab ntawd:
- Hloov cov teeb liab txiav txim ncaj qha mus rau lub tsev ua yeeb yam hauv tsev los ntawm kev sib txuas HDMI, lossis
- Hloov lub PCM teeb liab mus rau analog rau cov zis los ntawm ob lossis ntau lub suab analog tawm mus rau lub tsev ua yeeb yam uas muaj cov khoom siv sib xws.
Vim tias lub teeb liab PCM tsis muaj kev sib txuas, nws yuav siv ntau qhov chaw sib kis ntau dua. Yog li ntawd, yog tias koj siv digital optical los yog coaxial txuas los ntawm koj lub DVD lossis Blu-duab tshav Disc player mus rau lub tsev ua yeeb yaj kiab, tsuas muaj chaw txaus los hloov ob txoj hauv PCM suab. Qhov xwm txheej ntawd zoo rau CD playback, tab sis rau Dolby Digital lossis DTS ib puag ncig cov teeb liab uas tau hloov mus rau PCM, koj yuav tsum siv HDMI kev sib txuas rau tag nrho cov suab ib puag ncig vim tias nws tuaj yeem hloov mus txog yim raws ntawm PCM suab.
Yog xav paub ntxiv txog yuav ua li cas PCM ua haujlwm ntawm Blu-ray Disc player thiab lub tsev ua yeeb yam, saib rau hauv Blu-ray Disc player audio settings: bitstream vs. PCM.
