miniDSP Ltd, Hong Kong /
www.minidsp.com
/ Features and specifications subject to change without prior notice
8
Computer connectivity is used to perform acoustic measurements and generate digital room correction filters.
Up to four sets of correction filters can be stored on the
DDRC-88D
processor and recalled from the front panel
or via an infrared remote. Once the processor is fully configured, the computer is no longer needed.
1.2
H
OW
D
IRAC
L
IVE
®
WORKS
The miniDSP
DDRC-88D
audio processor includes Dirac Live®, a premium mixed-phase room correction
technology. This technology is used not only in home stereo and home theater systems but also in cinemas,
recording studios, and luxury cars.
As with any room correction system, Dirac Live®
corrects the system’s
magnitude response
(often referred to
imprecisely as “frequency response”
). In contrast to fully automated systems, Dirac Live® corrects the
magnitude response towards a user-adjustable
target response
. The target response takes account of the
natural frequency range of the loudspeaker system and the normal effects of loudspeaker dispersion on the
measured
in-room
magnitude response.
In addition, Dirac Live® corrects the system’s
impulse response
, which reflects how the system responds to a
sharp transient such as a drumbeat. Reflections, diffraction, resonances, misaligned drivers, and so on, all
combine to smear out the transient. An ideal loudspeaker has none of these, so correcting the impulse response
makes the speaker in the room behave much more like that ideal loudspeaker. The impulse response is a critical
factor for accurate sound-staging, clarity and bass reproduction. Dirac Live® employs a sophisticated analysis
algorithm to make the optimal correction across the
whole
listening area, not just at a single point.
Dirac Live® accomplishes this using
mixed-phase filters
–
filters that match a desired magnitude response
and
generate a customized impulse response. This contrasts with the
minimum-phase
and
linear-phase
filters that
are commonly used in audio applications. While minimum-phase and linear-phase filters are relatively easy to
design, they are tightly constrained in their impulse response characteristics
–
neither can make a desired
change to the magnitude response independently of controlling the impulse response. In some cases, they may
even make things worse.
Mixed-phase filters are more difficult to design, but the audible performance of Dirac Live® is due to its success
in using mixed-phase filters to make the system response across the
whole
listening area more closely resemble
that of an ideal speaker. The energy from the direct wave and from early reflections is optimally combined to
arrive as a single wave front to the listener. Late reflections are left largely untouched, being corrected only for
their spectral coloration, as they contribute to a larger, more enveloping soundstage.
Illustration of Dirac Live® magnitude and impulse response correction
