1.CVC thiab DSP suab nrov txo:
Thaum cov neeg siv khoom yuav Bluetooth headsets, lawv ib txwm hnov CVC thiab DSP suab nrov txo cov haujlwm uas cov tub lag luam muaj los txhawb lub mloog pob ntseg. Txawm tias muaj pes tsawg tus neeg siv tau hnov cov lus piav qhia, ntau tus neeg siv khoom tseem tsis nkag siab qhov txawv ntawm ob. Qhov txawv, rau xws li ib tug technical teeb meem, peb tuaj rau science ntawm ob nyob rau hauv lub hauv paus ntsiab lus ntawm kev ua hauj lwm thiab qhov sib txawv.
DSP yog ib qho luv luv rau kev ua cov teeb liab digital. Nws txoj hauv kev ua haujlwm: lub microphone khaws cov suab nrov ib puag ncig, thiab tom qab ntawd los ntawm lub suab nrov txo qhov ua haujlwm hauv lub pob ntseg, nws rov ua dua los ua kom rov qab suab nthwv dej sib npaug rau lub suab nrov ambient, uas tshem tawm suab nrov thiab ua tiav ntau dua. Zoo suab nrov txo cov nyhuv.
CVC yog luv rau Clear Voice Capture. Nws yog software suab nrov txo technology. Lub hauv paus ntsiab lus yog txhawm rau tshem tawm ntau hom suab nrov reverberation los ntawm kev tsim cov suab nrov tshem tawm software thiab microphone.
Qhov txawv raws li hauv qab no:
ib. rau cov khoom sib txawv, CVC thev naus laus zis feem ntau yog rau cov ncha generated thaum lub sijhawm hu, DSP feem ntau yog rau lub suab nrov nrov hauv qhov chaw sab nraud.
b. Cov neeg tau txais txiaj ntsig sib txawv, DSP thev naus laus zis feem ntau ua rau cov neeg siv lub mloog pob ntseg cov nyiaj tau los, thiab CVC feem ntau tau txais txiaj ntsig rau lwm tus.
Hauv cov ntsiab lus, lub mloog pob ntseg siv DSP thiab CVC suab nrov txo cov cuab yeej tuaj yeem txo cov suab nrov ntawm qhov chaw sab nraud ntawm kev hu, thiab txhim kho qhov zoo ntawm kev hu thiab lub suab ntawm lub mloog pob ntseg.
2.ANC suab nrov txo:
ANC hais txog Active Noise Control, uas nquag txo cov suab nrov. Lub hauv paus ntsiab lus yog tias lub suab nrov txo qhov ua rau rov qab suab tsis sib npaug rau lub suab nrov sab nraud, ua rau lub suab nrov. Daim duab 1 yog daim duab schematic ntawm feedforward nquag nrov nrov tshem tawm pob ntseg. ANC nti tau muab tso rau hauv lub pob ntseg. Ref mic (reference microphone) sau cov suab nrov ntawm lub pob ntseg. yuam kev mic (Error Microphone) Sau cov suab nrov tom qab txo suab nrov hauv lub pob ntseg. Tus neeg hais lus ua si lub suab nrov tom qab ua tiav ANC.
Daim duab 2 yog ib daim duab schematic ntawm ANC system, nrog peb txheej, sib cais los ntawm cov kab dashed. Lub hauv paus tseem ceeb tshaj plaws yog cov acoustic channel los ntawm ref mic mus rau qhov yuam kev mic, cov lus teb ua haujlwm yog sawv cev los ntawm P(z) P(z); nruab nrab txheej yog cov analog channel, qhov thib ob txoj kev yog txoj hauv kev los ntawm kev hloov pauv lim tawm mus rau qhov rov qab seem. Xws li DAC, rov tsim kho lim, lub hwj chim amplifier, hais lus playback, rov tau txais, pre-amplifier, anti-aliasing lim, ADC; cov txheej hauv qab yog txoj hauv kev digital, qhov kev hloov pauv hloov mus tas li kho cov lim qhov hnyav coefficient kom txo cov seem seem kom txog thaum sib xyaw. Txoj kev daws teeb meem feem ntau yog siv cov lim hloov pauv siv FIR lim ua ke nrog LMS algorithm. Simplify daim duab 2 thiab tau daim duab 3.
Cia kuv luv luv tham txog cov hauv paus ntsiab lus ntawm kev hloov lim dej thiab LMS (tsawg kawg txhais tau tias square) algorithm, thiab tom qab ntawd daim duab 3. Raws li pom hauv daim duab 4, muab cov tswv yim xx thiab qhov xav tau tso tawm dd, cov lim hloov hloov tshiab cov coefficients txhua iteration thiaj li. qhov sib txawv ntawm qhov tso zis yy thiab dd ua me thiab me kom txog thaum cov residual yog zero thiab converges. LMS yog qhov hloov tshiab algorithm rau cov lim dej hloov pauv. Lub hom phiaj ua haujlwm ntawm LMS yog square ntawm qhov yuam kev instantaneous e2(n) = (d(n)−y(n))2e2(n)=(d(n)−y(n))2, txhawm rau txo qis Lub hom phiaj muaj nuj nqi, Siv qhov gradient qhovntsej thiaj tsis mob muab cov qauv tshiab ntawm cov algorithm. (Lub tswv yim algorithmic ntawm kev siv gradient qhovntsej thiaj tsis tuaj yeem txo lub hom phiaj thiab tau txais cov qauv tshiab ntawm qhov ntsuas uas yuav tsum tau nrhiav yog ntau heev, xws li linear regression.) Cov mis hloov tshiab ntawm LMS algorithm siv FIR lim yog: w(n + 1) ) = w(n)+μe(n)x(n)w(n+1)=w(n)+μe(n)x(n), where μμ is step size. Yog tias qhov μμ loj hloov nrog iteration, nws yog ib kauj ruam-ib-kauj ruam LMS algorithm.
Wb tham txog daim duab 3. Ntawm no yog qhov kev hloov pauv lim tawm tom qab S(z)S(z) los piv nrog cov kev xav tau tso tawm. S(z)S(z) yuav ua rau instability. Nyob rau hauv cov ntaub ntawv, "lub teeb liab yuam kev tsis yog 'txhim kho' Nyob rau hauv lub sij hawm nrog rau cov kev siv teeb liab", lub convergence ntawm LMS yog tawg. (Kuv tsis tau paub tias nws txhais li cas T__T) Ib txoj hauv kev zoo yog FXLMS (Filtered-X LMS), uas tso cai rau x(n) nkag rau LMS module ntawm Sˆ(z)S^(z), Sˆ( z S^(z) yog qhov kwv yees ntawm S(z)S(z) Lub hom phiaj ntawm FXLMS:
E2(n)=(d(n)−s(n)∗[wT(n)x(n)])2,
E2(n)=(d(n)−s(n)∗[wT(n)x(n)])2,
Yog li gradient = −2e(n)s(n)∗x(n)−2e(n)s(n)∗x(n), qhov twg s(n)s(n) tsis paub, nrog rau nws kwv yees kwv yees, yog li ntawd FXLMS Hloov cov qauv yog
w(n+1)=w(n)+μe(n)x'(n),
w(n+1)=w(n)+μe(n)x'(n),
Where x'(n)=sˆ(n)∗x(n)x'(n)=s^(n)∗x(n).
Thaum cov lim hloov hloov pauv, E(z) = X(z)P(z)−X(z)W(z)S(z)≈0E(z)=X(z)P(z)−X(z) ) W(z)S(z) ≈ 0, so W(z) ≈ P(z) / S(z) W(z) ≈ P(z) / S(z). Qhov ntawd yog hais tias, qhov hnyav coefficient ntawm lub lim hloov pauv yog txiav txim siab los ntawm txoj hauv kev thawj thiab theem nrab ntawm lub mloog pob ntseg. Thawj txoj hauv kev thiab txoj hauv kev thib ob ntawm lub mloog pob ntseg yog qhov ruaj khov, yog li qhov hnyav coefficient ntawm cov lim dej hloov tau kuj ruaj khov. Yog li ntawd, rau lub hom phiaj ntawm kev yooj yim, qhov hnyav coefficients ntawm qee lub tuam txhab ANC lub mloog pob ntseg raug txiav txim siab ntawm lub Hoobkas. Tau kawg, qhov kev mloog ntawm ANC lub pob ntseg no yog qhov tseeb tsis zoo li ANC lub mloog pob ntseg nrog lub ntsiab lus hloov kho tiag tiag, vim tias nyob rau hauv qhov xwm txheej tiag tiag, lub suab nrov sab nraud cuam tshuam rau kev taw qhia ntawm lub pob ntseg, qhov kub thiab qhov sib txawv tuaj yeem cuam tshuam rau. cov lus teb channel ntawm lub mloog pob ntseg.
Matlab pov thawj
Sau Matlab code, siv cov lim hloov pauv ntawm cov kauj ruam me me LMS, cov txiaj ntsig simulation tau pom hauv daim duab 5. Hauv qhov ntau ntawm 0 txog 2 kHz, feedforward ANC yog siv los tshem tawm Gaussian dawb suab nrov, thiab lub suab nrov attenuation yog 30 dB + nyob nruab nrab. FXLMS nyob rau hauv Matlab tsev qiv ntawv yog tsau-kauj ruam, thiab cov nyhuv yog phem dua.
Q&A
ib. Vim li cas ANC tsuas yog rau lub suab nrov qis qis dua 2 kHz?
Ntawm ib sab, lub cev lub suab rwb thaiv tsev ntawm lub mloog pob ntseg (passive nrov txo) tuaj yeem thaiv cov suab nrov nrov, thiab nws tsis tas yuav siv ANC los txo cov suab nrov nrov. Ntawm qhov tod tes, lub suab nrov tsawg zaus muaj qhov ntev wavelength thiab tuaj yeem tiv taus qee theem qeeb, thaum lub suab nrov nrov muaj qhov luv wavelength thiab rhiab rau theem sib txawv, yog li ANC tshem tawm cov suab nrov nrov.
b. Thaum qhov kev ncua hauv hluav taws xob loj dua qhov kev ncua sij hawm tseem ceeb, yuav ua li cas thiaj li txo tau qhov kev ua tau zoo ntawm cov algorithm?
P(z) ncua me me, S(z) ncua yog loj, xws li P(z) = z-1, S(z) = z-2, tsuas yog thaum W(z) = z tuaj yeem ua tau raws li qhov yuav tsum tau ua, tsis yog -ua rau, tsis tuaj yeem.
c. Dab tsi yog qhov txawv ntawm Feedforward ANC, nqaim-band feedforward ANC, thiab tawm tswv yim ANC?
Cov qauv Feedforwad muaj ref mic thiab ib qho yuam kev mic uas sau cov suab nrov sab nraud thiab sab hauv seem seem, feem. Cov qauv kev tawm tswv yim tsuas muaj ib qho yuam kev mic, thiab cov teeb liab siv tau tsim los ntawm kev ua yuam kev mic thiab hloov cov zis lim tawm.
Broad-band feedforward yog cov qauv piav qhia saum toj no. Nyob rau hauv lub nqaim-band qauv, lub suab nrov generates ib tug teeb liab teeb liab generator, thiab lub teeb liab generator generates ib tug siv teeb liab rau lub adaptive lim. Tsuas yog siv tau los tshem tawm cov suab nrov raws sijhawm.
Kev tawm tswv yim ANC siv yuam kev mic kom rov qab tau cov teeb liab sau los ntawm ref mic hauv cov qauv feedforward vim nws tsuas muaj qhov yuam kev mic. Txoj kev tsis txaus siab rau qhov kev txwv tsis pub muaj, yog li tsuas yog cov suab nrov uas tuaj yeem kwv yees tau, piv txwv li lub suab nrov ntawm lub sijhawm luv luv, raug tshem tawm. Nws yuav tsum tau muab sau tseg hais tias yog hais tias lub feedforward tsis txaus siab rau lub causal txwv, piv txwv li, hluav taws xob ncua ncua sij hawm ntev tshaj lub ntsiab channel acoustic ncua, nws tsuas muaj peev xwm tshem tawm cov nqaim band lub sij hawm suab nrov.
Kuj tseem muaj Hybrid ANC qauv uas suav nrog ob qho tib si feedforward thiab tawm tswv yim qauv. Lub ntsiab kom zoo dua yog tias koj tuaj yeem txuag qhov kev txiav txim ntawm cov lim dej hloov.
