User manual R3
DLCP
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4
Hypex Filter Design
After setting the right hardware settings, you’ll have to configure the software side. This is done by
pc software, called Hypex DSP filter design. Please do not connect any speakers to your system yet!
4.1
Target response
To target a linear phase response from a loudspeaker may not always be optimal. When the phase
response of a system is perfectly linear and the amplitude response still has minor ripples on it,
these ripples translate equally to time responses before and after the central impulse. Psychoacous-
tic masking of pre-echos is orders of magnitude less than masking of post-echos.
If a minimum phase response is targeted, no energy will be produced before the impulse. This ex-
plains the paradox that listeners often report a minimum phase loudspeaker to have a “tighter im-
pulse response” than a linear phase one.
4.2
Driver correction
Loudspeaker units are minimum phase systems. That is, minus any acoustical delay the phase and
log magnitude characteristics are eachother’s Hilbert transform. One property of minimum phase
systems is that all zeros lie on the left half plane (s domain) or inside the unit circle (z domain). The
poles always do, of course. Thus all poles and zeros can be canceled using IIR filters. FIR filters are
not needed to equalize the drivers’s phase response. The phase response gets automatically equal-
ized as the magnitude response is corrected using minimum-phase EQ. A consideration to be made
is whether to iron out every last wrinkle or how much roughness is still permissible in the response.
One should realize that narrow bumps and troughs in the frequency domain correspond to responses
long after the main event in the time domain, usually reflections that change markedly with speaker
and listener positioning excessive correction of the on-axis response is guaranteed to make the off-
axis response much worse.
4.3
Crossover design
A common practice in DSP based loudspeakers is to fit the acoustic response of individual drivers to
a linear phase high pass/low pass response. Unless the listener is exactly on-axis and in an anechoic
room, the pre-ringing of both responses will not cancel perfectly. Because of this, it may be more
productive to optimize only the sum, not the individual driver response. Here too, IIR filters are a
more natural choice than the seemingly obvious FIR filter.
4.4
Software installation
System requirements:
•
Pentium class or higher
•
64MB RAM
•
USB1.0 or higher
Tested on Windows XP and Vista
All files are compressed in the setup.zip file. This zip file contains 1 DLL file for communication and
an .EXE file, which represents the Hypex DSP filter design program.
1.
Unzip the setup.zip file on your hard disk
2.
Open the “Hypex filter design.EXE” by double clicking the file
