28
48 76 48
b
0
28
48 76
b
1
S
28
48 76
b
2
76
28
76 48
a
1
28
76 48
a
2
M0012-01
z
–1
z
–1
Magnitude
Truncation
z
–1
z
–1
2.6BassandTrebleControls
TAS5518C
8-ChannelDigitalAudioPWMProcessor
SLES238A–SEPTEMBER2008–REVISEDJULY2009
www.ti.com
ThedirectformIstructureprovidesaseparatedelayelementandmixer(gaincoefficient)foreachnodein
thebiquadfilter.Eachmixeroutputisasigned76-bitproductofasigned48-bitdatasample(25.23format
number)andasigned28-bitcoefficient(5.23formatnumber),asshowninFigure2-12.The76-bitALUin
theTAS5518Callowsthe76-bitresolutiontoberetainedwhensummingthemixeroutputs(filter
products).
Thefive28-bitcoefficientsfortheeachofthe56biquadsareprogrammableviatheI
2
Cinterface.See
Table2-3.
Figure2-12.BiquadFilterStructure
AllfivecoefficientsforonebiquadfilterstructurearewrittentooneI
2
Cregistercontaining20bytes(orfive
32-bitwords).ThestructureisthesameforallbiquadsintheTAS5518C.Registers0x51–0x88showall
thebiquadsintheTAS5518C.Notethatu[31:28]bitsareunusedanddefaultto0x0.
Table2-3.ContentsofOne20-ByteBiquadFilterRegister(Default=All-Pass)
INITIALIZATIONGAINCOEFFICIENTVALUE
DESCRIPTIONREGISTERFIELDCONTENTS
DECIMALHEX
b
0
coefficientu[31:28],b0[27:24],b0[23:16],b0[15:8],b0[7:0]1.00x00,0x80,0x00,0x00
b
1
coefficientu[31:28],b1[27:24],b1[23:16],b1[15:8],b1[7:0]0.00x00,0x00,0x00,0x00
b
2
coefficientu[31:28],b2[27:24],b2[23:16],b2[15:8],b2[7:0]0.00x00,0x00,0x00,0x00
a
1
coefficientu[31:28],a1[27:24],a1[23:16],a1[15:8],a1[7:0]0.00x00,0x00,0x00,0x00
a
2
coefficientu[31:28],a2[27:24],a2[23:16],a2[15:8],a2[7:0]0.00x00,0x00,0x00,0x00
From32-kHzto96-kHzdata,theTAS5518Chasfourbassandtrebletonecontrols.Eachcontrolhasa
±18-dBcontrolrangewithselectablecornerfrequenciesandsecond-orderslopes.Thesecontrolsoperate
fourchannelgroups:
•L,R,andC(channels1,2,and7)
•LS,RS(channels3and4)
•LBS,RBS(alternativelycalledLandRlineout)(channels5and6)
•Sub(channel8)
For176.4-kHzand192-kHzdata,theTAS5518Chastwobassandtrebletonecontrols.Eachcontrolhas
a±18-dBI
2
Ccontrolrangewithselectablecornerfrequenciesandsecond-orderslopes.Thesecontrols
operatetwochannelgroups:
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