T-44/48 Series Amplifier
Operation Manual
T-44/48 Series | rev.
firm. 1.258 and above
30
4.3.3 Delay
The delay page controls the amount of delay associated with the output channel
selected and is adjustable from 0 to 998ms. The delay parameter is adjustable in fine steps at
low values; the adjustment becomes progressively coarser as the value increases.
4.3.4 High and Low pass Filters
High pass and low pass crossover filtering is provided for the output signal. Filter type is
selectable from 1
st
order,
Butterworth, Bessel, Linkwitz-Riley, Hardman
and
LIR
Linear Phase.
Filter slopes of up to 8th order or 48dB / octave are provided. Not all filter types are available in
all slopes. For example 18dB / octave Linkwitz-Riley filters cannot be selected because they do
not exist.
The Hardman type filter is always described by its’ order as the filter becomes
progressively steeper rather than following a linear slope so a dB/octave description is not
accurate.
4.3.5 LIR Crossover Filtering
Designed by
Linea Research
TM
to
Tecnare T-44 Series
, “Linear Impulse Response”
(LIR) crossover filtering gives a Linear Phase crossover which has a constant delay regardless
of frequency (unlike other types of crossover which delay different frequencies to a different
extent, thus smearing the arrival time). The
LIR
crossover can thus be described as having a
flat Group Delay response, and thus entirely free of Group Delay Distortion, this is exactly the
same as can be provided by common FIR filtering but without the complications and
disadvantages inherent with the FIR technique.
The shape of the LIR crossover filter is similar to a 4
th
order Linkwitz-Riley filter, and
maintains zero phase difference between the adjacent bands across the crossover region to
keep the polar response rock steady.
Linear Phase filtering necessarily introduces delay; the laws of physics demand it. To
keep this delay to a minimum, it is recommended that more conventional crossover shapes
(such as Linkwitz-Riley) are used for the very lowest frequency high-pass edge, particularly if
this is less than perhaps 100Hz, which is well below the frequency thought to cause audible
‘Group Delay Distortion’.
This constant delay will depend on the lowest high-pass frequency used in the
crossover filters in a given Drive Module.
Also see the section on Latency Delays on page 35.
4.3.6 Parametric Equalisation and All-Pass Filters
There are ten different EQ filters; two shelving filters and eight parametric filters.
Parametric filters are defined by frequency, bandwidth and gain. The frequency is controlled
over the ranges from 10Hz to 25.6kHz. The bandwidth, shown as Width on the screen, is
controlled over ranges from 0.10 octaves to 5.2 octaves. Bandwidth can be shown and adjusted
as
Q
or
Octaves
(Oct). Gain is adjustable in 0.2dB increments.
Any of the six Parametric filters can be used as
All-Pass filters
. When a filter is set to
All-Pass mode, the Gain parameter value will show as “AllPass” on the display. This setting may
only be engaged by right-clicking the EQ ‘icon’ in the EQ window of the System Engineer panel.
Also see Bandwidth Units in Utilities on page 33.
