TC Electronic DB4 MKII - Manual (Page 14)

MDX 5.1
10 DB4 / DB8 MKII Algorithms
Fig 5.
MDX 5.1 Level Diagram for different Steer and
Threshold settings.
“Defeat Threshold” relates to DXP Threshold
which relates to “Ref Level”. “Limit Threshold”
only relates to Digital Full Scale output level.
The Ref Level parameter on the Main page sets
the unity gain point for all channels (unless gain
offsets are applied), see Fig 5.
The Thresholds on the DXP pages are relative
to Ref Level, so in this particular drawing, Ref
Level is set at -12 dBFS, while most DXP Thresh-
olds are set at -16 dB. If you invoke the Defeat
Threshold, gain reverts to unity for “below radar”
input levels. Defeat Threshold is relative to DXP
Threshold. In the drawing, the Defeat Threshold
is set at -20 dB.
Note, that the lower the DXP Threshold, or the
higher a Steer setting, the more low level boost
is applied. The low level boost can be different
in different channels, and even in different fre-
quency bands.
Also observe that the Limiter threshold setting is
not relative to Ref Level, but always referenced
to output full scale.
Reading the Gain Meters
Gain meters in indicate absolute gain. The upper
segments of a meter gives an indication of the
boost and frequency response applied to low
level signals, while the lower segments of a me-
ter gives an indication of the current (dynamic)
gain and frequency response, see Fig 6.
In this example, low level signals are subject to
a 5 dB boost in the Low and Hi band. The Low
frequency band is currently attenuated by 2 dB,
while the Mid and Hi bands are at 0 dB gain.
Fig 6.
Example of MDX 5.1 Gain Meter. The me-
ter shows max low level gain and spectral re-
sponse, plus current gain and spectral re-
sponse. In the example, the Low band is cur-
rently attenuated by 2 dB, while Mid and Hi
bands are at unity gain (0 dB).
Adjustment Tips
The easiest way to specify the yellow area of Fig
1 is to set an appropriate difference between the
Ref Level parameter and the Limit Threshold.
Wide dynamic range material for a high reso-
lution delivery might be broadcast with a sub-
stantial difference between the two, for instance
15 dB or more.
If the audio bandwidth is low, and the listener
environment presumably noisy, the difference
between Reference and Limit Thresholds should
smaller. For heavily data reduced multi-channel
broadcast, best results are typically obtained
with a 6 to 10 dB difference.
When significant data reduction is to be used,
also be careful not to allow peaks going all the
way to 0 dBFS. Consider bringing down the Limit
Threshold between 1 and 4 dB. Judge the qual-
ity of loud, spacious material passing through
MDX 5.1 plus data reduction plus decoding,
while listening to the output of the data reduc-
tion decoder. Pay special attention to transient
distortion, and if the sound image collapses at
high levels.