Coding suab ntaub ntawv

Tej txheej txheem yuav tau hloov dua siab tshiab rau hauv cov ntawv no. Yog li, encoding suab ntaub ntawv ntawm computers yog nqa tawm raws li nram no:

- cua deeg kaw rhiab pab kiag li lawm;

- tua hloov dua siab tshiab rau hauv ib qho hluav taws xob tam sim no, nyob rau lub zaus (amplitude) mas nws txawv raws li;

- lub resulting tam sim no yog sampled, i.e. muaj yog nws zauv (tej zaum hais tias tuas binary encoding suab ntaub ntawv).

Cov uas ua analog hluav taws xob thawj suab txaus yuav zoo dua, ntau dua qhov lub zaus ntawm qhov kev kuaj ntawm ib tug piv txwv thiab coding tob.

Nyob rau hauv lwm yam lus, encoding ntawm lub suab ntaub ntawv - yog ib tug paub cov txheej txheem hloov ntau analog teeb liab mus rau hauv ib tug digital, npaj rau ntxiv ua rau qhov kev tsim nyog ntaus ntawv. Cia peb xav txog cov kauj ruam thiab cov hau kev ntawm digitizing suab.

Discretization ntawm lub sij hawm ncej - yog lub hauv paus rau digitizing. Raws li Kotel'nikova theorem, lub analogue hluav taws xob lub teeb liab yuav digitized los ntawm kev nyeem ib tug tej yam kauj ruam ntawm ib tug tas mus series ntawm qhov tseem ceeb ntawm nws cov amplitude. Tus zaus ntawm xws readings yuav tsum muaj tsawg kawg yog ob zaug cov kev txwv zaus ntawm lub ntsiab teeb liab. Yog hais tias tsim nyog, digitizing analogue "qhov code" mus rau lub operating zaus ntawm 0-20 kHz zauv yuav tsum tau nqa tawm tsis tsawg tshaj li 40 txhiab. Times ib ob (40 kHz). Piv txwv hais txog cov xov tooj ntawm kev ntsuas ib ob analog teeb liab qhov chaw (piv txwv, cov zauv zaus). Nrog ua qauv nce tsis tau tsuas yog qhov zoo tshaj tab sis kuj lub ntim ntawm lub resulting cov ntaub ntawv kwj.

Tsis tas li ntawd, lub suab ntaub ntawv coding yuav tsum tau ua nyob rau hauv lwm txoj kev. Raws li, piv txwv li, los ntawm digitizing lub nonuniform quantizer, tej zaum hu ua logarithmic. Thaum uas siv cov tag nrho amplitude ntau conditionally muab faib mus rau hauv khej uas muaj thiab tsis muaj qhov tseem ceeb. Ntxiv encoding suab ntaub ntawv no tshwm sim los ntawm kev thov loj nyiaj ntawm quantization theem nyob rau hauv qhov chaw nrog ib tug me me amplitude nqi (thiab vice versa). Nco ntsoov, txawm li cas los, hais tias tag nrho cov xov tooj ntawm cov theem tseem tib yam li nyob rau hauv lub niaj quantization qauv (PCM).

Ib tug nkaus txawv mus kom ze yog siv nyob rau hauv ib txoj kev encoding txoj kev. Nws yog hu ua "txawv Pulse Code Tes taws los piav» (DPCM). Nrog xws li ib tug txoj kev yog tsis raug quantization ntawm lub amplitude ntawm qhov ncaj lub teeb liab thiab nws cov txheeb ze tus nqi. Raws li ib tug tshwm sim tau mus cuag yuav txo tau ntawm lub ntim nyob los ntawm cov ntaub ntawv, vim lub mechanism yog ua tom ntej twv ua ntej ntawm tus thawj lub teeb liab kuaj.

Lub coding thiab ua suab ntaub ntawv piav nyob rau hauv daim ntawv no yuav tsum tau ua hloov dua siab tshiab "analog-rau-digital". Qhov no tus txheej txheem no tau siv ib tug ADC (analog-rau-digital converter). Nrog rau qhov no ua lag luam, txhua ntaus ntsib txhua hnub computer tswv nruab nrog ib lub suab card (nyob rau hauv cov ntaub ntawv no muaj ib tug rov qab txheej txheem - tau txais lub analog teeb liab los ntawm lub digital kwj).

ADC zog yog raws li nram no:

- tsawg zaus bandwidth. Siv cov ntxaij lim dej, lub teeb liab Cheebtsam yog txiav, lub zaus ntawm uas - ntau tshaj ib nrab ntawm cov zauv zaus (yog vim li cas piav ua ntej lawm).

- Xaiv ntawm cov amplitude qhov tseem ceeb tu ncua. Cov uas ua analog teeb liab yog sawv cev los ntawm ib tug sib lawv liag ntawm ib cov khoom ntawm qhov ntau thiab siv (discretization).

- Hloov ntau tau txais khoom lawv ze qhov tseem ceeb ntawm ib tug taag set (quantization).

- Hloov txhua quantized nqi ntawm cov zwj ceeb xov tooj ntawm quantization ntau ntau (txhua nqi - nws serial tooj). Qhov no yog qhov dhau theem ntawm Digitisation.