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with Fixed-Point Direct-Form FIR Filters  This example shows how
to design FIR filters implemented with the direct-form structure
using fixed-point arithmetic. This example requires a Fixed-
Point Designer™ license.  See also Getting Started with Fixed-
Point Filters  Designing the Filter  The FIR filter to use is
not critical. Since we will use the direct-form structure, it
doesn't even need to have linear phase. For this example we will
use a simple least-squares design.
f=fdesign.lowpass('N,Fp,Fst',80,.11,.19); % Specifications  A
filter object results from the design method. It associates
coefficients with a particular filter structure, here a direct-
form FIR structure.  h = design(f, 'firls', 'Wpass', 1, 'WStop',
100, ...     'FilterStructure', 'dffir'); h =
FilterStructure: 'Direct-Form FIR'           Arithmetic: 'fixed'
Numerator: [1x81 double]         PersistentMemory: false
CoeffWordLength: 16