TC Electronic Broadcast 6000 - Manual (Page 149)

Brickwall 2
English Manual 145
Brickwall 2
The Brickwall Limiter occupies:
– @ Normal Sample Rate: 1/4 DSP Resource
– @ Double Sample Rate: 1/4 DSP Resource
The inputs and outputs of this algorithm are dis-
tributed as follows:
Input Output
L
E1
E2
E3
E4
L
R R
Introduction
Do we need another Limiter?
Several golden ears in pro audio believe that the
best sound in pop/rock music generally was pro-
duced between 1982 and 1995. Despite higher
resolution in converters and DSP, lower jitter and
probably a better overall understanding of digital
media, we seem to be on a declining rather than
inclining sound quality slope these years; even
though people buying records and film may not
be aware of it.
Obviously, there could be many reasons for this
we cannot directly influence: Trends, basic re-
cording and microphone placement skills, more
semi-pro equipment being used, shorter pro-
duction times and therefore less attention to de-
tail etc.
The last couple of years, however, TC through
papers given at AES conventions has proven
that at least one good reason for trashy end
listener and radio sound exists: The abuse of
loudness maximizers in mastering. When levels
get squashed against full scale, 0 dBFS, recon-
structed intersample peaks in DA and sample
rate converters may be considerable higher than
the level downstream equipment was designed
to handle. We call this level “0 dBFS+”, and no
current rules in mastering prevents such peaks
from happening.
The BrickWall limiter is designed:
1) to investigate if your signal is contaminated
with 0 dBFS+ peaks
2) to remove them.
If you are concerned about audio quality at the
end listener, or have a desire to conserve talent,
we believe you need a limiter with these virtues.
The BrickWall limiter cannot prevent destruction
of dynamic range from happening at earlier stag-
es in the production process, but it can get rid of
the signals we know are going to get distorted in
consumer CD players, radio processors or data
reduction codecs.
Precision in Level and Time
The BrickWall limiter operates with extended
precision in both level (48 bit throughout) and
time (5 times oversampling). Double precision
calculations are always used, while hyper-preci-
sion in limiter timing can be turned on or off us-
ing the Upsample key.
Level meters are always upsampled in order to
identify intersample and 0 dBFS+ peaks on In-
puts as well as Outputs. The meter scale is ex-
tended to +3 dBFS because excessive level nor-
mally falls between 0 and +3 dBFS, and most
consumer equipment already exhibits severe
distortion at +0.5 dBFS.
We recommend using the BrickWall limiter in
Upsample mode. However, if you wish to just
limit the signal based on sample by sample val-
ues like a normal digital limiter, the function can
be turned off. When turned off the limiter does
not protect against 0 dBFS+ peaks from occur-
ring.
Limiter Time constants
Another important feature of Brickwall 2 is its
adaptive time constants. Several internal tim-
ing parameters and detection variables are con-
stantly updated to combat low frequency distor-
tion while maintaining quick adoption to occa-
sional peaks. Control is applied modeling analog
dynamics behavior in order to avoid introducing
discontinuities and out of band dirt to the signal.
Years of research into static, dynamic and
0 dBFS+ distortion in digital dynamics process-
ing is built into Brickwall 2 when Adaptive is ac-
tivated. Therefore, the use of Adaptive Profiles is
recommended. If you turn off the Adaptive set-