TC Electronic Broadcast 6000 - Manual (Page 151)

Brickwall 2
English Manual 147
More information
… About 0 dBFS+ signals, required headroom in
the signal path, behavior of consumer CD play-
ers and production equipment can be found at
the TC website, from which technical papers
about related issues also can be downloaded.
Brickwall 2 algorithm – main page
Brickwall 2 algorithm – main page
Input Gain Left and Right
Range: ±24 dB
Overall Gain/Drive control at the input of the lim-
iter. Once the threshold has been set, this is a
convenient place to adjust more or less dynam-
ics processing and loudness.
The Gain parameter offers the same “Drive” ap-
proach to level and threshold used in classic
analog limiters. Unlike analog designs, however,
Brickwall 2’s 48 bit internal resolution prevents
resolution and signal/noise ratio from being sac-
rificed, because the processing dynamic range
is larger than even the highest resolution input
would be.
If bit transparency and/or conservation of bit
patterns are of essence, note the green indica-
tors above the Gain controls. When they are lit,
bit shifts are used for gain control rather than
rounded calculations where bit patterns are re-
shuffled. For instance, if a 1 bit shift up is used
as Gain (+ 6.0 dB), the antidote 1 shift down
(-6.0 dB) can be used at the output Fader to as-
sure 24 bit transparency, when the signal is be-
low the threshold of limiting. If the Fader instead
remains at 0.0 dB, the input bit pattern is still
preserved, but the bits are shifted one position
towards MSB.
Green Input Gain LED indicator
Indicates bit transparency (read introduction for
details).
Link
Press to Link L and R Gain controls and the
sidechains. Note that phase and delay controls
work independently of this setting. If the limiting
threshold is frequently hit with music, link the
channels to stabilize the stereo image. For dialog
or un-correlated instruments, best results may
be obtained by keeping the channels un-linked.
Green Limiter LED indicator
Indicates bit transparency (read introduction for
details).
Threshold
Range: Off, 0 dBFS to -25 dBFS
When the input level exceeds the Threshold,
the signal will be attenuated. Gain reduction
meters at the bottom of the display display the
max amount of reduction applied to either of the
channels. When Link is active, the same amount
of reduction is used in both channels.
Note: The architecture of Brickwall 2 enables
bit transparency to be obtained for any limiting
Threshold between Full Scale and -25 dBFS.
In CD mastering it is common practice to allow
level to digital Full Scale on a sample by sample
basis. This has the consequence that down-
stream equipment will behave unpredictably,
and in many cases add distortion you don’t hear.
The distortion is not harmonic, can be quite se-
vere (more than 10 %) and cause early listening
fatigue. Consult the Tech Library at the TC web-
site for more details. To get rid of most distortion
problems in most cases, make sure the Upsam-
ple key is pushed (green). Threshold can now
be set safely at 0.0 dBFS, while Brickwall 2 still
takes care of peaks that would otherwise cause
distortion. The alternative is to detect only single
samples (Upsample grey), like most processors
do, and lower the Threshold by 2 to 3 dB to ob-
tain the same degree of low distortion down-
stream performance. Besides from post produc-
tion and broadcast work, at least one mastering
situation exists where you should consider a
lower Threshold than 0 dBFS with upsampling
engaged: When dealing with material that will be