Digital Signal Processing Reference
In-Depth Information
plotted on a logarithmic scale,
referenced to a passband
frequency response of one.
We can verify our hand calculation was correct. We calculated
the magnitude of
j
H
(
p
/2)
j
at 3, and
j
H
(0)
j
at 13. The logarithmic
difference is:
20 log
10
(3 / 13)
12.7 dB
If you check the frequency response plot above, you will see at
frequency F
s
/ 4 (or 0.25 on the normalized frequency scale),
which corresponds to
ΒΌ
p
/ 2 in radians, the filter does indeed seem
to attenuate the input signal by about 12 to 13 dB relative to
j
H
. Other filter programs might plot the frequency axis refer-
enced from 0 to
(0)
j
p
, or from
p
to
p
.
