Product Information

9
Elettromedia
62018 Potenza Picena (MC) Italy
T [phone] - F [phone]
elettromedia.com
audison.com
All specications subject to change without notice_19.A
IIR digital lters faithfully simulate analog lters (active or
passive), approximating phase and frequency behavior. Like
their analog equivalents, they are affected by unavoidable phase
rotations at the cut-off frequency, which are different based on
the type of curve used (Butterworth, Linkwitz, Bessel), however
still perceived when listening.
In practice, for instance, a fourth-order low-pass IIR lter (24 dB /
Oct) at 200 Hz cut-off, plus a high-pass symmetric lter, results in
a phase rotation ranging from 0 to -360 degrees along the whole
audio spectrum. This phase alteration
affects the perception of the sound image, which highlights
inaccuracies in terms of coherence and stability. Think of a 3-way
system where the door-mounted 18 cm woofer is 400 Hz crossed
with the middle-range, installed on the a-pillar next to a tweeter,
itself crossed with the middle-range at 5.000 Hz, using crossovers
with IIR lters. The system phase alteration reduces the focus of
the instruments on the virtual stage. For this reason, a number of
audio enthusiasts prefer to adopt 2-way systems with a woofer
and tweeter crossing at 2.500 Hz with a slope of 6 dB / Oct, so
as to limit phase rotations as much as possible. This solution,
however, presents a number of signicant disadvantages, mainly
due to increased distortion and lower tweeter power. With a
slope of only 6 dB / Oct., the music signal around the cut-off
frequency is simultaneously generated by tweeters and woofers
to a considerable extent. Since a tweeter and a woofer have
very different electro-acoustic parameters, the sum of the two
emissions does not produce clear output signals, which results in
less clarity in the reproduction of musical transients.
FIR CROSSOVER FILTERS
+10
+5
0
-5
-10
dB
Hz
20 30 50 70 100 200 400 700 1k 2k 3k 5k 7k 10k 20.0k
FIR EQUALIZATION (Finite Impulse Response)
+90
+45
0
-45
-90
dB
Hz
20 30 50 70 100 200 400 700 1k 2k 3k 5k 7k 10k 20.0k
Image 5: electric frequency response simulation (module and phase),
of the two poles of the parametric equalizer featuring IIR lters
(in black) and FIR lters (in blue).
FIR
IIR
Phase Magnitude
+10
+5
0
-5
-10
dB
Hz
20 30 50 70 100 200 400 700 1k 2k 3k 5k 7k 10k 20.0k
CROSSOVER FIR FILTERS
+90
0
-90
-180
-270
-360
deg
Hz
20 30 50 70 100 200 400 700 1k 2k 3k 5k 7k 10k 20.0k
Image 4: electric frequency response simulation (module and phase)
of low-pass Linkwitz-Riley fourth order crossover (24 dB/Oct) summed
with a symmetrical high-pass featuring a 200 Hz cut-off frequency. IIR
lters (in black) and FIR lters (in blue).
FIR
IIR
Phase Magnitude