TC Electronic SYSTEM 6000 MKII Algorithm Manual

64
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Introduction
Do we need another Limiter?
Several golden ears in pro audio believe that the best
soundinpop/rockmusicgenerallywasproduced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 recording and microphone
placementskills,moresemi-proequipmentbeingused,
shorter production times and therefore less attention to
detail 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,
reconstructed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“0dBFS+”,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
 0dBFS+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 stages 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-precision in limiter timing can be turned
on or off using the Upsamplekey.
Level meters are always upsampled in order to identify
intersampleand0dBFS+peaksonInputsaswellas
Outputs.Themeterscaleisextendedto+3dBFSbecause
excessivelevelnormallyfallsbetween0and+3dBFS,
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valueslikeanormaldigitallimiter,the
function can be turned off. When turned off the limiter does
notprotectagainst0dBFS+peaksfromoccurring.
Limiter Time constants
Limiter Time constants
AnotherimportantfeatureofBrickwall2isitsadaptivetime
constants. Several internal timing parameters and detection
variables are constantly updated to combat low frequency
distortionwhilemaintainingquickadoptiontooccasional
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 processing is built into
Brickwall2whenAdaptiveisactivated.Therefore,theuse
of Adaptive Profiles is recommended. If you turn off the
Adaptive setting, internal variables other than Release
Time will be fixed.
Absolute Bit Transparency
WhenevertheBrickWalllimiterisnotattenuatingthesignal,
it is passed completely unaffected, transparent to the 24th
bit.Consequently,theBrickWalllimitermaybeusedto
remove0dBFS+peaksonalreadymasteredandfinally
dithered material. When the Limiter is bit transparent, a
green indicator next to the Threshold control lights up.
Input and Output gain controls have 0.1dB increments, but
snap to bit shifts at 0, 6, 12, 18 and 24dB settings. When
a bit shift value is selected, a green indicator is lit on the
screen. Bit transparency from Input to Output is obtained
whenInputGainandOutputFaderhitthesevaluesand
sumto0dB,e.g.Input/Output0/0dB,-6/+6dB,-12/+12dB
etc.
Bit Pattern Transparency
When only bit shift gain settings are used on Input and
Output, bit patterns remain unchanged through the
algorithm, but can be shifted up (in the MSB direction) or
down(intheLSBdirection)asdesired.E.g.Input/Output
+6/0(oneup),0/-12(twodown).
Linking
ThetwochannelsBrickWalllimiterscanbeoperated
independentlyorlinked.Ifpronouncedlimitingisperformed
onstereomaterial,linkingshouldbeconsideredtoavoid
L/R image shifts. If only mild and occasional limiting is
beingdone,un-linkedoperationevenonstereomaterial
may sound the best.
The Brickwall Limiter occupies:
@ Normal Sample Rate : 1/4 DSP Resource
@ Double Sample Rate : 1/4 DSP Resource
Algorithm Inputs/Outputs are distributed as follows:
E1 - E4
L
R
L
R
INPUT
OUTPUT
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TC Electronic SYSTEM 6000 MKII Specifications

General

Brand	TC Electronic
Model	SYSTEM 6000 MKII
Category	Computer Hardware
Language	English