Z Systems rdq-6 User manual

rdq-6 instruction manual z-systems audio laboratories
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rdq-6instructionmanual
rdq-6 instruction manual....................................................................................................................................................1
introduction............................................................................................................................................................................1
physical layout.......................................................................................................................................................................3
•front panel controls................................................................................................................................................3
•rear panel layout .....................................................................................................................................................4
operational guide .................................................................................................................................................................5
•input selection.........................................................................................................................................................5
•stereo-linked/dual-mono mode.........................................................................................................................6
•output wordwidth (dither) selection................................................................................................................6
•volume control.........................................................................................................................................................7
•individual volume offsets.....................................................................................................................................8
•channel selection....................................................................................................................................................9
•bypass mode............................................................................................................................................................9
Transparent Tone Control.............................................................................................................................................11
•selecting filters.......................................................................................................................................................11
memory functions ..............................................................................................................................................................13
•save preset..............................................................................................................................................................13
•load preset..............................................................................................................................................................14
appendix A: equalization and dither.............................................................................................................................15
•equalization............................................................................................................................................................15
•dither........................................................................................................................................................................18
appendix B: the relationship between Q and slope................................................................................................22
appendix C: finite wordlength digital filtering..........................................................................................................23
appendix D: rdq-6 automation protocol ...................................................................................................................25
•Automation Port Reconfiguration ...................................................................................................................25
•Command Strings.................................................................................................................................................25
specifications........................................................................................................................................................................28
precautions...........................................................................................................................................................................29
warranty.................................................................................................................................................................................30
•other z-systems audio laboratories products...............................................................................................30
•contact information..............................................................................................................................................31
introduction
Congratulations on your purchase of the rdq-6 digital reference equalizer. The rdq-6 is the
result of many years of research and development in digital audio technology, and when used
properly, it will create a home theater experience you may not have thought possible from
your system.
The purpose of this document is to give you a complete understanding of the theory and
operation of the rdq-6 so that you may apply it properly in your home theater system. The
rdq-6 is a six channel digital tone and level control system that is used between an AC-3 or
DTS decoder and six channels of digital-to-analog conversion (realizable as either three
separate two-channel DACs or a single six-channel DAC such as our rdac-6). This is shown
schematically in Figure 1. The rdq-6 offers six bands of parametric equalization for each of six
discrete channels. The parametric equalization can be used for a wide array of purposes,

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including room correction, speaker matching, speaker compensation, or tonal shaping.
Additionally, the rdq-6 allows the user to control master volume, individual channel volume
offsets and dither all in the digital domain. With the rdq-6 in the signal path, there is no need
for an analog preamplifier; the DAC(s) can be connected directly to the power amplifier(s). In
this regard, it is useful to think of the rdq-6 as a digital domain preamplifier for your six-
channel home-theater playback.
The rdq-6 can also be used in a mode we call "super-two-channel mode" (S2 mode). When in
S2 mode, the rdq-6 can apply all of its equalization bands to a two-channel source, yielding
18 bands of parametric equalization per channel. This allows the rdq-6 to function much like
our rdp-1 and rdq-1 processors, but with more power and flexibility. For example, twelve of
the equalization bands could be used for room and speaker correction while the remaining
six are used as tone controls.
FIGURE 1
The rdq-6 also has a number of useful memory features that make it extremely versatile,
flexible, and easy to configure. The following pages will give you a simple “walking tour”
through the rdq-6. Appendices A, B, and C provide more detailed information.

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physicallayout
•front panel controls
Figure 2 shows the front panel in normal operating mode. Below, you will find a description
of all of the front panel controls on the rdq-6.
FIGURE 2
1. Display. 4 row by 40 character.
2. Signalvalidindicators. Separate LEDs indicate the presence of valid digital input signals
on the Left/Right Front, Left/Right Surround and the Center/Sub channels.
3. Bypass button. Pressing this button disengages all of the rdq-6's signal processing (with
the exception of the volume control) from the signal path.
4. Display dim/off. Pressing this button cycles the display through 5 different intensity
settings: 100%, 60%, 40%, 20%, and "off."
5. System menu button. Allows the user to access the input selection, load and save
functions, output wordwidth controls and the stereo/dual mono link controls.
6. Menu buttons. These multi-function buttons work in conjunction with the display. In
the normal operating mode shown above, pressing one of these buttons will bring the
filter shown directly above it "into focus." When in any other mode, the last row of the
display will show a menu bar. There will be six options on this menu bar, one per menu
button, across the bottom of the display. Pressing any of these buttons will execute the
corresponding function described by the word displayed directly above it on the menu
bar. All six buttons may or may not be active, depending on the mode. To aid in
understanding this, the illustrations in this manual will have the buttons "greyed out"
when they are not active in a particular mode of operation.

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7. Control knobs. The three large knobs on the front panel are used to change parameters
shown in the display. All three knobs may not always be active. To aid in understanding
this, the illustrations in this manual will have the knobs "greyed out" when they are not
active in a particular mode of operation.
8. Volume control button. Pressing this button puts the rdq-6 into a mode where either
the main volume or the individual channel volume offsets can be controlled.
9. Channel selection button. Pressing this button toggles the display and knobs between
the available channels. When a new channel is chosen, the display will show all of the
filter parameters for that channel.
10. Infra-redremotesensor.
•rear panel layout
The only audio connectors visible on the rdq-6's rear panel are three sets of XLR AES/EBU
digital inputs and outputs and three sets of RCA S/PDIF digital inputs and outputs. The main
power switch and the AC mains connector are also located on the rear panel. This is shown
in Figure 3.
FIGURE 3
1. Left/Right Front (Left/Right Room Eq 1) digital processor card.
2. Left/Right Surround (Left/Right Room Eq 2) digital processor card.
3. Center/Sub (Left/Right TTC) digital processor card.
4. S/PDIF digital outputs on RCA connectors.
5. AES/EBU digital outputs on XLR connectors.
6. S/PDIF digital inputs on RCA connectors.
7. AES/EBU digital inputs on XLR connectors.
8. Automation port.
9. AC power inlet module.
10. MAINS power switch.

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operationalguide
•input selection
The rdq-6 has three independent digital processor cards, Left/Right Front, Left/Right
Surround, and Center/Sub. Each of these cards has two digital inputs and two digital outputs.
The rdq-6 allows you to select which of the inputs is active through the input selection
function. There are a number of reasons why input source selection is best performed in the
digital domain. The most significant is the reduction of crosstalk. There is infinite rejection
between input channels on the rdq-6; crosstalk is simply not possible.
FIGURE 4
How to do it. Each digital processor card accommodates the digital audio input and output
for a stereo pair of channels. On each card, you will find 1 AES/EBU input on an XLR
connector, 1 S/PDIF input on an RCA connector, 1 AES/EBU output on an XLR connector, 1
S/PDIF output on an RCA connector. Regardless of which input is selected, both outputs are
active simultaneously. To select which input is used by the rdq-6, press the system button
and select the INPUT submenu. The display will appear as shown in Figure 4. To change the
active input, simply rotate the knob below the input selection display for each of the three
digital processor cards. To switch to S2 Mode, press the TO S2CH button. Doing this will
cause the screen to present a confirmation display. You should remember that the output of
the rdq-6 in S2 mode appears on the Center/Sub processor card outputs. When you have set
your DAC properly, hitting the CONTINUE button will complete the transition to S2 mode.
While in S2 mode, the board labels will change to L/R room eq 1, L/R room eq 2, and L/R TTC.
Pressing the button below BACK will take you to the system menu and pressing the button
below EXIT will take you to the normal operating mode.

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•stereo-linked/dual-mono mode
The Left/Right Front and Left/Right Surround digital processor cards can be configured to run
in either stereo-linked or dual-mono modes. In stereo-linked mode, the controls and displays
pertain to both the left and the right channels simultaneously. When changes are made to
any parameter, both channels will be affected. In dual-mono mode, you have independent
control of the left and right audio channels. The center/sub processor bank is always in dual-
mono mode.
FIGURE 5
How to do it. Press the system button and select the LINK submenu. The display will
appear as shown in Figure 5. To change the link mode, simply rotate the knob below the link-
mode selection display for the front and surround processor cards. If in S2 mode, the L/R TTC
label will also be shown and the link status for this board can be changed as well. Pressing
the button underneath BACK will take you to the system menu and pressing the button
underneath EXIT will return you to the normal operating mode.
•output wordwidth (dither) selection
For a more thorough discussion of dither, please refer to Appendix A.
The rdq-6 allows you to control the dither for each processor card so that each of the output
signals are compatible with your digital-to-analog converter(s). The rdq-6 carries out its
computations in 40-bit floating-point arithmetic, which then must be converted back to a
fixed-point representation usable by your DACs. Internally, the 40-bit result is first converted
to 24-bit fixed-point. The dither control then determines how many bits appear at the outputs
of the rdq-6 and how those bits are obtained. You can choose from:
•24 bits
•truncated to 20 bits (no dither)
•dithered to 20 bits
•truncated to 16 bits (no dither)
•dithered to 16 bits

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The rdq-6 allows you to set different output wordwidths and dither settings for each of its
three processor cards so that you can use different DACs for each channel pair. The majority
of DACs today use 20-bit digital-to-analog chips as their core conversion technology; hence,
we tend to recommend the 20-bit dithered output as the most useful across the broadest
spectrum of source material and DACs today. If you are using the rdq-6 with the z-systems
rdac-6, you can take advantage of the full 24-bit output. As 24-bit converters and 24-bit
digital filter chips become more commonplace, we will recommend the 24-bit output setting
for other devices.
FIGURE 6
Howtodoit. To select which dither mode is used by the rdq-6, press the system button and
select the WORD submenu. The display will appear as shown in Figure 6. To change which
dither mode is used, simply rotate the knob below the dither selection display for each of the
three processor cards. Pressing the button underneath BACK will take you to the system
menu and pressing the button underneath EXIT will take you to the normal operating mode.
•volume control
The analog volume control is a potential source for noise and coloration. Nonetheless, most
of us are willing to live with these problems in light of the other problems that life without a
volume control would cause! The rdq-6 features a digital-domain volume control and offset
facility which is utterly neutral tonally. This control allows you to apply between +12 dB of
boost and -95 dB of cut to the incoming digital signal and an offset between +12 dB of boost
and -95 dB of cut to every channel with respect to the left front channel. You may have heard
arguments that digital-domain volume control is undesirable because it leads to loss of
resolution. This may be true for poorly implemented digital volume controls but certainly is
not the case for the rdq-6. Remember the discussion of dither: we can achieve resolution well
below the least significant bit. This is the key to the rdq-6’s digital volume control (please
refer to appendix B for a more detailed explanation).

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FIGURE 7
How to do it. With the rdq-6 in normal operating mode, press the volume button. The
display will change as shown in Figure 7. To change the master volume, turn the center knob
until the desired value is shown on the display. You can also enter offsets relative to the left
front channel for the right front, left and right surround, center and sub channels. Please refer
to the next section for instructions on how to do this.
A special note about the rdq-6’s volume control. The rdq-6 always powers up to a default
master volume of –40 dB. Furthermore, volume is the only parameter not stored or recalled
by the load and save functions, nor is it affected by the bypass control. This is for an
important reason. Dangerous output levels could result when using the rdq-6 in a system
with no analog preamplifier. For example, suppose we designed the rdq-6 so that the bypass
control returned the volume to 0 dB. Hitting bypass during a loud passage would then result
in the system volume going to full-scale. The same could happen while comparing presets. It
is for this reason that the volume setting is unaffected by the load and save functions and
bypass; whatever the value of volume is dialed in will remain in place during preset loads or
during bypass.
•individual volume offsets
In a home theater system, it is not at all uncommon that the speakers may have markedly
different sensitivities from one another. Consequently, it is often necessary to be able to
control the relative levels of the signals going to each of the speakers. This is why we have
included a channel volume offset facility.
How to do it. If you are not yet in the volume screen, hit the volume button. Next, select a
channel for which to set an offset by pressing one of the buttons located directly underneath
FRONT, SURR and C/SUB to access the front, surround and center/sub offset screens. Figure 8
shows how the display will appear if the FRONT offset was chosen. Now, we have chosen the
Left Front channel as the offset reference. That is, all of the offsets will be relative to the Left
Front channel. Consequently, you will not be able to change the +00.0 dB shown for this
channel. Dial in an offset using the knob underneath the displayed offset you would like to
change.

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FIGURE 8
•channel selection
The rdq-6's display is only large enough to display the complete set of filter parameters for
one channel at a time. The purpose of the channel selection button is to scroll between the
filter parameters for each of the channels.
FIGURE 9
How to do it. With the rdq-6 in normal operating mode, press the channel button. Figure 9
shows how the display looks when we are displaying the the Left/Right Front channel
settings. To change which channel is being displayed, turn the center knob until the channel
you would like to see is shown. If either the front or surround processor cards are in stereo-
linked mode, you will not see the individual left and right channels for these banks; they will
be displayed as a stereo pair. The same is true for the TTC pair if it is linked mode. If you
would like to apply tone control separately to the left or right channels of either of these two
banks, please see the section entitled stereo-linked/dual-mono mode.
•bypass mode
Hitting the bypass button results in the state shown in Figure 10. The bypass modesets all of
the filters flat, cancels the dither and returns all of the volume offsets to 0 dB; only the master

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volume is left unchanged. When in bypass mode, none of the rdq-6’s controls are functional;
you must press bypass again to return to normal mode.
FIGURE 10
aspecialnoteonperformingA/Bcomparisons
The italicized text above makes it clear that the bypass control returns the output wordwidth
to 24 bits, canceling the dither that may have been selected. Perhaps most significantly,
however, the bypass mode does not affect the volume. This is because we want it to be
impossible for the user to accidentally bring the volume to full-scale. Because the bypass
mode cancels the dither, hitting bypass when the volume is set to anything other than 0 dB
can result in very subtle sonic differences due to truncation, depending on the program
material and the volume. Therefore, doing a level-matched comparison between a given EQ
setting and flat EQ using the bypass control is not really meaningful unless the volume is set
to 0 dB. A better approach is to set up a preset with all of the filters set flat and the dither set
as desired and use that preset in the A/B-compare mode.