Yuav ua li cas yog AAC-hom ntawv?

Rau hnub tim, AAC-hom tseem tsis tau mus txog qhov loj muab faib rau ntawm lub suab muaj, Txawm li cas los, ib tug xov tooj ntawm tsis nws yog superior rau tag nrho cov tam sim no hom ntawm cov suab compression, thiab yog li ntawd tsim nyog peb saib.

Yuav ua li cas yog nws?

Peb pib nrog ib tug txhais: audio hom AAC yog proprietary (patented) ib compression suab ntaub ntawv. Nyob rau tib lub sij hawm nws muaj ib tug me me tsis zoo thaum lub sij hawm coding tshaj MP3 nyob rau tib lub ntsis nqi tej yam kev mob. Tsis tas li ntawd, AAC-hom ntawv yog ib tug wideband suab coding algorithm uas siv ob lub ntsiab encoding ntsiab cai no los ho txo tus naj npawb ntawm cov ntaub ntawv yuav tsum tau rau kis tau tus mob ntawm high-zoo cov suab. Cov tshuaj no yog pom tias yuav tsum yog ib tug ntawm lub siab tshaj plaws zoo, muag nyob rau ntawm ib tug tsis ntawm compression technology. Cov hom ntawv txhawb tseem niaj hnub khoom, txawm portable. Nws yuav tsum tau muab sau tseg hais tias lub nplhaib tones nyob rau hauv AAC hom yuav tau muas ntawm tus iTunes cia, thiab nyob rau hauv no khw yog suab paj nruag, compressed thiaj tau tuaj los ntawm txoj kev txiav txim siab. Nws yuav tsum raug hais tias lub AAC-hom Ameslikas tsim raws li ib tug successor mus MP3, uas yuav muab tau paub zoo coding. Qhov kev txiav txim luam tawm nyob rau hauv 1997 raws li ib tug tshiab, 7, ib feem ntawm ib tsev neeg ntawm MPEG-2.

hauv paus ntsiab lus ntawm cov lag luam

Thaum maub nyob rau hauv hom ntawv no, cov nram qab dab: imperceptible Cheebtsam ntawm lub teeb liab raug muab tshem tawm, ntxuav ntawm cov kho lub teeb liab redundancy. Tom qab ntawd, cov ntaub ntawv tiav nyob rau hauv raws li txoj kev raws li cov MDCT lawv complexity. Thaum lub theem tom ntej cov lis dej num no ntxiv rau kho ntau yam nrog uas tsis. Thaum kawg, lub teeb liab yog kis tau los yog dim.

Tag nrho cov ntsiab lus

Interestingly, lub AAC-hom muaj ib tug zauv zaus ntawm nruab nrab ntawm 8-96 kHz thiab tus naj npawb ntawm raws nyob rau hauv lub luv 1-48. MP3 Hybrid siv ib tug txheej ntawm cov ntxaij lim dej. Nws yog hais txog ib tug hloov discrete cosine txia, nyob rau hauv lem AAC ntawm ib tug nce tus nqi ntawm "qhov rais", uas nce mus txog 2048 ntsiab lus.

Yog li, AAC ntau npaum li cas haum rau encode lub suab kwj muaj lub complex mem tes thiab square-yoj Pib ntsais koj teeb, muab piv nrog MP3. Hom tau lub peev xwm los dynamically hloov nyob rau hauv lub MDCT thaiv lengths nyob rau hauv ntau 2048-256 cov ntsiab lus. Yog hais tias muaj yog ib tug luv luv lub sij hawm los yog ib tug tib ua haujlwm, siv ib tug me me "qhov rais" rau 256 ntsiab lus nyob rau hauv thiaj li yuav ua tau zoo dua kev daws teeb meem. Nyob rau hauv cov ntaub ntawv no, lub neej ntawd yog 2048-point loj "qhov rais" maximize lub coding efficiency. AAC muaj ib tug xov tooj ntawm zoo piv nrog rau cov ib txwm MP3. Cov lawv peb yuav tsum hais: lub realization ntawm ib tug loj tus naj npawb ntawm cov suab raws (mus txog 48), tseem ceeb coding efficiency nyob rau hauv tej yam kev mob ntawm qhov thiab nce mus nce los me ntsis nqi thiab piv txwv zaus nyob rau hauv ntau ntawm 8 Hz 96 kHz (rau MP3, qhov no daim duab yog los ntawm 8 Hz rau 48 kHz) thiab ib tug ntau saj zawg zog tshwj xeeb hom hu ua Joint tso suab. Raws li rau cov ntsiab, "AAC +" - ib tug codec uas yog teem rau kev ua hauj lwm nrog cov uas tsis muaj me ntsis nqi. Yog ib tug ua ke ntawm SBR thiab AAC LC, li no tsis tau raws li zoo suab twb nyob rau hauv lub chav 32-48 kbit / s.