Analog Devices VISUALDSP++ 3.5 Manual page 500

DSP Run-Time Library Reference
The characteristics of the filter are dependent upon filter coefficients and
the number of stages. Each stage has five coefficients which must be stored
in the order
B2
and should be scaled accordingly. This requires that the value of the A0
A2
coefficient is greater than both
coefficients should be stored in
ber of stages.
The
iir_fr16
rithm. When importing coefficients from a filter design tool that
employs a transposed direct form II, the
to be negated. For example, if a filter design tool returns
0.2, -0.9]
[1.0, -0.2, 0.9]
Each filter should have its own delay line which is a vector of type
and whose length is equal to twice the number of stages. The vector
should be initially cleared to zero and should not otherwise be modified by
the user program. The structure member
the delay line.
Algorithm
− 1
+ +
B B z
( ) = 0 1
H z
− 1
− −
1 A z
1
where
= +
D A * D A
m 2 m − 2
= +
Y B * D B
−
m 2 m 2
where m={0,1,2,...,n-1}
Domain
-1.0 to +1.0
4-84
, , , , . The value of
B1 B0 A2 A1
A1
s->c
function is implemented using a direct form II algo-
, then the A coefficients have to be modified to
.
− 2
B z
2
− 2
A z
2
+
* D x
1 m − 1 m
+
* D B * D
−
1 m 1 0 m
VisualDSP++ 3.5 C/C++ Compiler and Library Manual
is implied to be 1.0 and
A0
and for all the stages. A pointer to the
A2
, and should be set to the num-
s->k
and
A1
should be set to the start of
s->d
coefficients have
A2
A = [1.0,
A =
fract16
for ADSP-219x DSPs
A1