Antares MDT user manual

							MDT UserÕs Manual61
Release Slider
The Release slider adjusts the time it takes for MDT to return to its quies-
cent state after a peak comes through. The range of the control is from 0 mil-
liseconds to 5,000 milliseconds. The current release time is displayed in the
window to the left of the slider. 
Clicking on the arrows changes the release time in small increments. Press-
ing on the arrows decrements/increments the release time continuously.
Pressing  before clicking or pressing on the arrows decrements/
increments the release time in 1 millisecond steps. The thumb wheel can be
dragged for making gross adjustments.
Reset Button
Clicking the Reset Button zeros the Input Offset values shown in the Input
Offset Window.
Setting Menu
The Setting menu contains the list of settings that are stored in the MDT
Preferences Þle in the System Extensions folder. Any number of settings can
be saved in the Setting menu.
To save a setting; 
1. Choose Save Settings AsÉ from the Settings menu.
A dialog box appears requesting a setting name.
2. Type the desired name in the text box and click on Save. 
						

							MDT Reference
62MDT UserÕs Manual
The settings are now saved. These settings appear at the bottom of the 
Setting menu.
To recall a setting;
1. Choose it from the Setting menu.
The settings are recalled as you saved them.
To delete the setting;
1. Choose Delete SettingsÉ from the Setting menu.
A dialog appears with the list of the settings in the menu.
2. Scroll down to Test and select it by clicking on it.
3. Click on the Delete button.
The setting is deleted from the menu. You may select multiple settings 
for deletion by shift-clicking or click dragging over the items to be 
deleted. To make a non-contiguous selection, press  and 
click on the items to select them. Note that the settings themselves 
remain on MDT until they are moved or another setting is chosen.
TDM Settings and the Compare Button
The ProTools 4 TDM settings feature has been implemented. The TDM set-
tings recall all control values (all buttons and sliders) as well as the I/O
curve. Although recalling these settings is not automated as the MDT Set-
tings menu has been, the TDM settings features do offer additional ßexibil-
ity in selecting Þle storage options.
The ProTools 4 ÒCompareÓ button has been implemented. This provides
automatic comparison between the current TDM setting and the existing
control values (including the I/O curve points). By pressing the ÒCompareÓ
button, you can instantly exchange these settings, effectively doing an A/B
comparison. 
When the ProTools 4 TDM settings feature or the ÒCompareÓ button are
used, the MDT Settings menu is restored to the saved status. However, the
remaining control settings reßect other restored values rather than values
from the MDT Setting menu item 
						

							MDT UserÕs Manual63
Thresholds And Terminators
Up to 30 thresholds can be placed on the In/Out Grid to Òrubber bandÓ the
I/O Curve. The rules for using thresholds are as follows.
To: Do This:
place a threshold on the curve,  click in the In/Out Grid. 
display the location of a threshold click on the threshold
move an existing threshold, click and drag it to the new location. 
delete a threshold,  press  and click on the threshold.
The lower terminator is ÒgluedÓ to the In axis. It will always have an Out
value of -96 dB. It can never exist to the right of a threshold, that is, have a
higher input value than a threshold. This is to prevent the I/O Curve from
having more than one output value for any given input value.
The upper terminator is glued to the Out axis. It will always have an In
value of 0dB.
Variable Button
MDT is unbelievably smooth because it removes pumping by compressing
spectral bands separately. However, the most problematic aspect of MDT
(and all multiband compressors) is created by the multiband feature: When
some spectral bands are hotter than others, they are compressed more,
thereby coloring the sound. 
THRESHOLD
Lower TerminatorUpper Terminator 
						

							MDT Reference
64MDT UserÕs Manual
Setting this button causes the input offset levels to be continuously adjusted
so the band levels are, on the average, even with one-another. This causes
the output sound to have no coloration. The speed of these adjustments is
three times slower than the compressor release time. Hence, no matter what
the release time setting is, using the ÒVariableÓ button will not interfere
with the bands compressing independently from one-another. Once the
ÒVariableÓ button is set, pressing any other level control (ÒFlatÓ, ÒResetÓ or
the input offset arrows) pops it out.
IMPORTANT:
The ÒVariableÓ button requires CPU processing to work. MDT does this pro-
cessing when it is given control of the CPU to update meters. MDT is not
given the CPU when the plugin is not visible. Hence, the ÒVariableÓ button
will not work when the plugin is not visible. In order to achieve the effect of
the ÒVariableÓ button when the plugin is not visible, you must record the
resulting input offset level changes using automation in ProTools 4. 
						

							MDT UserÕs Manual65
CHAPTER 5Theory of Operation
MDT has been designed to provide enormous power and ßexibility through
the use of a simple user interface. However, since MDT is a new technology,
some users may Þnd it interesting or helpful to have a deeper
understanding of the conceptual elements of MDTs actual processing
algorithms. 
This chapter has been written to satisfy that need. The concepts behind
MDTs processing algorithms are presented here in sufÞcient detail so that
the behavior of MDT is precisely explained. To provide as much simplicity
as possible, the various sections of this chapter describe the processing that
occurs for monaural sound data. The last section of the chapter describes
how MDT processing occurs for a stereo sound source.
The Gain Adjust Algorithm
The most basic computation in MDT is the Gain Adjust. In the various
diagrams in this chapter, the Gain Adjust computation is represented by the
symbol:
The purpose of the Gain Adjust computation is to perform the gain
computation on one channel of data. This includes computing the signal
level, scaling the level according to the user deÞned input level offset value,
Gain Adjust 
						

							MDT UserÕs Manual66 The Gain Adjust Algorithm
and computing and applying the Þnal gain. The details of the Gain Adjust
computation are given by the diagram:
The diagram above shows that as each sound sample is presented, a new
input level is computed. The input level is a positive valued number
between 0 (-96 dB) and 1 (0 dB). The input level is then multiplied by the
user deÞned input level offset value to give the scaled input level. This
value is presented to the user on the In/Out Grid as a horizontal bar. It is
then used as the input setting on the I/O Curve to look-up the output level.
The output level is divided by the input level to produce the output gain. 
As an example of this processing, consider the case where the I/O Curve is
a 45 degree 1:1 diagonal. In this case, the output level will always equal the
scaled input level and the resulting output gain will always be unity. This
means the sample output will be identically equal to the sample input.
Each incoming sound sample is also stored in a Þrst in/Þrst out (FIFO)
buffer. To compute the output sound, samples are taken from the FIFO
buffer. This is represented in the diagram above as delay. The amount of
delay introduced by MDT is shown in the Delay Window. 
For example, suppose the I/O Curve represents a compressor plus gain.
Soft sound data would result in a high output gain. With no delay, if the
sound were to become loud more quickly than the attack time, the high
output gain would be applied to the loud sound resulting in output
overßow and clipping. With a delay present, the output gain would be
reduced before the delayed sound arrives, and a reduced output gain
would be applied to the data, preventing overßow and clipping.
It is important to distinguish the use of the input level offset. This value
only changes the displayed level, the corresponding output level look-up
from the I/O Curve, and the gain computation. In this way, the input level
offset serves only to change the position on the I/O Curve from which the
gain is computed.
compute
leveloutput
gain input
leveloutput
levelmultiplyinputoutput
output level
Ö input levelmultiply
input level offset
delay
scaled
input
level 
						

							MDT UserÕs Manual67 The Gain Adjust Algorithm
In the Gain Adjust computation, the compute level box depicts the
computation of the input level from the sound samples. The compute level
computation is depicted in the ßowchart:
This ßowchart shows that the absolute value of each sound sample is Þrst
compared with the previously computed level. If the absolute value is
greater than the previously computed level, then a decay value
corresponding to the attack time is used, otherwise a decay value
corresponding to the release time is used. (The decay values are positive
and slightly less than one, which result the proper decay or release times.)
The decay value is then used to update the level value using the equation
shown in the ßowchart. When the attack time is shorter that the release
time, the resulting level approximates the largest instantaneous amplitudes
in the data. Other settings result in levels that are less than the largest
instantaneous amplitudes in the data.
absolute
valueinput
abs
level > abs
?
new level
level 
						

							MDT UserÕs Manual68 The ÒFull BandÓ Filter Mode
The ÒFull BandÓ Filter Mode
This is the simplest computation. In this Þlter mode, the sound data is input
to the Gain Adjust. The output of the Gain Adjust is multiplied by the Gain
slider value for the Þnal output:
The ÒStandardÓ Filter Modes
The following diagram depicts the Ò3 bandÓ and Ò5 BandÓ Þlter modes:
The input signal is Þrst split into separate bands using parametric equalizer
Þlters. Each of these Þltered signals is processed by a separate Gain Adjust
algorithm. Hence each band embodies separate input level computations
and well as separate gain computations. The delays in each of the Gain
Adjust computations are the same. Hence no phase effects are present from
differing delays. After the Gain Adjust computation, the separate bands are
summed together and multiplied by the Gain slider value to give the
output.
Gain Adjustoutputmultiply
Gain slider value
input
Filter 2
Filter nFilter 1
Gain Adjust
Gain Adjust
Gain Adjust
input
Parametric
Equalizer Filters
sumoutputmultiply
Gain slider value 
						

							MDT UserÕs Manual69 The ÒStandardÓ Filter Modes
The center frequencies of the parametric equalizer Þlter pass bands are 140,
1120, and 8960 Hz (3 octave spacing) for the 3 Band Þlters and 40, 160, 640,
2560, and 10240 Hz (2 octave spacing) for the 5 Band Þlters.
Consider the case where the I/O Curve is a 45 degree 1:1 diagonal. In this
case, all output levels will equal the scaled input levels and the resulting
output gains will be unity. This means the Gain Adjust output will equal the
Gain Adjust inputs. The resulting overall output will then have the transfer
function characteristic of the parametric equalizer. The graphs below show
the frequency response of the multiband Þlters with unity output gain.
FF F F
rr r r
ee e e
qq q q
uu u u
ee e e
nn n n
cc c c
yy y y
LL L L
oo o o
gg g g
      
MM M M
aa a a
gg g g
nn n n
iii i
tt t t
uu u u
dd d d
ee e e
      
(( ( (
dd d d
BB B B
)) ) )
10030010003000100002022050
-5
0
5
-1010
MDT 2.0 3 band transfer characteristic
FF F F
rr r r
ee e e
qq q q
uu u u
ee e e
nn n n
cc c c
yy y y
LL L L
oo o o
gg g g
      
MM M M
aa a a
gg g g
nn n n
iii i
tt t t
uu u u
dd d d
ee e e
      
(( ( (
dd d d
BB B B
)) ) )
10030010003000100002022050
-5
0
5
-1010
MDT 2.0 5 band transfer characteristic 
						

							MDT UserÕs Manual70 The ÒAPÓ Filter Modes
The ÒAPÓ Filter Modes
In some cases, the ±0.3 dB of passband ripple in the parametric equalizer
Þlters of the standard Þlter modes are not desirable. The AP Þlter modes do
not have these artifacts provided certain limitations can be met. The
following diagram depicts the Ò3 band APÓ and Ò5 Band APÓ Þlter modes:
This diagram is the same as the standard Þlter mode diagram except for the
additional data paths show as heavier lines. Consider the following sub-
diagram:
The triangle near the -1 shows the signal is multiplied by -1. In the case
where the I/O Curve is a 45 degree 1:1 diagonal, the output of the Gain
Adjust is identically equal to the input. Therefore the output of the sub-
diagram is zero. Referring now back to the larger diagram, the only input to
the ÒsumÓ is directly from the overall input, in which case, the output of the
AP Þlter mode is simply the Gain slider applied to the input with no
parametric equalizer Þlters artifacts.
When the I/O Curve deviates from a 45 degree 1:1 diagonal, output occurs
from the sub-diagram, and the characteristics of the re-combined signal
depend on the phase characteristics of the parametric equalizer Þlters.
SpeciÞcally, these Þlters are designed so that there is a zero degree phase
shift in the center of each pass band. Consequently, a gain increase
indicated by the I/O Curve results in a gain increase in the overall output
Filter 2
Filter nFilter 1
Gain Adjust
Gain Adjust
Gain Adjust
Parametric
Equalizer Filters
input
Gain slider value
sumoutputmultiply
-1
-1
-1
Gain Adjust
-1