Genex GXA8 Quick start guide

GenexResearch Limited
…………………………………………………………………………….
GXA8 Operational Manual
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Revision 1.0
interstage
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-pro audio with a smile

GXA8 Operational Manual Rev 1.0 Contents
Genex Research Limited Page i
Contents
CONTENTS........................................................................................................................................I
IMPORTANT NOTES........................................................................................................................1
Unpacking...................................................................................................................................1
Power.........................................................................................................................................1
Location......................................................................................................................................1
Mounting Positions......................................................................................................................1
Conformity..................................................................................................................................1
Technical Support.......................................................................................................................1
LAYOUT OF THIS MANUAL.............................................................................................................2
INTRODUCTION TO THE GXA8.......................................................................................................3
Description..................................................................................................................................3
OPTIONS .........................................................................................................................................3
FRONT PANEL DESCRIPTION ........................................................................................................4
Panel Buttons.............................................................................................................................4
AUDIO...............................................................................................................................................5
AUDIO FORMATS ..............................................................................................................................5
Standard Output Format .............................................................................................................5
Input/Output Formats Available Through Expansion Cards..........................................................5
AES Output Configuration...........................................................................................................5
Bits Out and Dither .....................................................................................................................6
Bit Split – Encode or Decode ......................................................................................................6
Audio Mute .................................................................................................................................6
CLOCKS...........................................................................................................................................7
Lock Mode..................................................................................................................................7
Precision.....................................................................................................................................7
Wide...........................................................................................................................................7
Clock Source..............................................................................................................................7
Master........................................................................................................................................7
External Word Clock...................................................................................................................7
Slot One .....................................................................................................................................7
Slot Two .....................................................................................................................................7
Sample Rate...............................................................................................................................7
METERS AND INPUT LEVEL...........................................................................................................9
Peak Hold...................................................................................................................................9
Fine PPM....................................................................................................................................9
Over Sensitivity...........................................................................................................................9
Input Gain Level..........................................................................................................................9
BACK PANEL.................................................................................................................................10
SPECIFICATION.............................................................................................................................11
A/D Performance......................................................................................................................11
Miscellaneous...........................................................................................................................11

GXA8 Operational Manual Rev 1.0 Important notes
Genex Research Limited Page 1
Important notes
Unpacking
After unpacking the GXA8, save all the packing materials in case you ever need to
ship the unit. Thoroughly inspect the GXA8 for signs of damage. Report any shipment
damage to the carrier at once. The following accessories are included with the
GXA8:-
1.Power Cable.
2.User Guide.
3.Four mounting feet and screws.
4.Four rack mounting bolts.
Power
•This unit is equipped with voltage-selectable linear power supply. Please ensure
that the correct voltage for you region is selected (110V or 220V) before plugging
into the supply.
•Make sure that the unit is turned off before connecting the power plug to the
socket.
•Please be sure to connect the power cord to the AC inlet on this unit before
connecting the power plug to the socket.
•When disconnecting the power plug from the socket, do not pull the cord but hold
the plug to avoid damaging the cord.
•Avoid damaging the power cord.
•If the unit is not to be used for a long period of time, unplug the cord from the
socket.
•It is normal for this unit to become warm whilst being operated.
Location
•Avoid using this device in extreme heat, humidity or where it may be affected by
dust or vibration.
•Do not place or drop anything heavy on the unit or its power cable.
•Ensure that the GXA8 has adequate ventilation space on all sides. We
recommend at least 1U rack space top and bottom.
Mounting Positions
Do not mount the GXA8 upside down.
Conformity
The GXA8 bears the 'CE' mark and is therefore fully compliant. Tests performed and
passed are as follows,
EN50082-1: 1992
EN55022: 1994 Class A
Technical Support
Technical Support is available on line through the Genex web site at
http://www.genex.co.uk/or by emailing: [email protected].

GXA8 Operational Manual Rev 1.0 Layout of this Manual
Genex Research Limited Page 2
Layout of this Manual
Sections in this manual appear in the following order.
1.A brief introduction to the feature set and a list of options.
2.A detailed front panel description with a functional description of every
front panel button and display. This section should be used as a quick
guide and reminder to basic front panel operations.
3.A description of the audio formats supported
4.An explanation of the clock structure
5.Rear panel schematics and connector details

GXA8 Operational Manual Rev 1.0 Introduction to the GXA8
Genex Research Limited Page 3
Introduction to the GXA8
Description
The GXA8 is a professional, 8-channel, analogue to digital audio converter,
supporting all standard sample rates from 44.1kHz up to 192kHz at resolutions of 16,
20 or 24 bits. It also supports the Sony DSD format (1-bit, 2.8224MHz sample rate
∆Σ) when married with the DSD upgrade kit (available separately).
All settings are available from the intuitive front panel with no complex menu
structures to navigate. The front panel also includes 8 high resolution peak power
meters (PPMs), one for each channel.
As standard, the GXA8 is fitted with four AES/EBU digital outputs providing eight
channels of digital audio output up to 96kHz and four channels of output for 192kHz
(an additional four channels are available via the AES expansion card). In addition,
expansion cards with ADAT, TDIF, SDIF and workstation interfaces on are available.
Options
•8-channel DSD upgrade kit. Includes the ∆Σmodulator i.c.s and the
output and processor card
•8-channel AES expansion input and output card
•ADAT input / output card
•TDIF input / output card
•8-channel SDIF2 output card
•Workstation input / output card

GXA8 Operational Manual Rev 1.0 Front Panel Description
Genex Research Limited Page 4
Front Panel Description
Panel Buttons
1. Mute
Mutes the digital audio output from the unit
2. Over Sensitivity
This button determines how many
consecutive maximum value sample will
trigger the “OVER” LED to light
3. Peak Delay
Sets the peak hold of the PPMs to either
on, delay (2 seconds) or off
4. Fine PPM
Changes the PPM mode to a scale of
±1dB centred around –12, -14, -16, -18
and –20dBFS to aid input level calibration
5. Clear Peak Hold
Clears any peak or over LEDs on the
PPMs that are lit
6. Configuration
Selects between the following input
sources: Analogue, slot one (digital) and
slot two (digital). In addition, for analogue
input the output format can be set to either
PCM or DSD (DSD required the DSD
upgrade kit)
7. Lock Mode
Selects between the “wide” and “precision”
lock modes when the unit is locked to an
external clock source.
8. Clock Source
Selects the clock source for the unit –
master (internal precision-cut quartz
crystal), external word clock, slot one or
slot two
9. AES Output
Chooses between single, dual or quad-
wire. Obviously, not all modes are
available for all sample rates
10. Bit Split
Selects whether to encode or decode (or
nothing) a PAQRAT bit-splitting format
(PCM mode) or a 4-wire “DSD over AES”
format (DSD mode, encoding only).
11. Bit Depth
Selects between 24, 20 or 16 bit fully
dithered output resolution.
12. Sample Rate
Allows selection of 44.1kHz, 48kHz,
88.2kHz, 96kHz, 176.4kHz and 192kHz.
This button does not function in DSD
mode (forced to 44.1kHz) or in slave clock
mode (locks automatically to input rate)
13. PPM DISPLAY
The PPM displays consists of eight
columns of 14 segments each,
representing channels 1 to 8 respectively.
The meters are digital and are calibrated
in dBFS, with the top segment
representing 0dBFS. Peak values can be
set to decay immediately, be held for 2
seconds before decaying, or can be held
until the CLEAR PEAK HOLD button is
pressed.
Note the overload segments remain on
until cleared by the pressing the CLEAR
PEAK HOLD button.

GXA8 Operational Manual Rev 1.0 Audio
Genex Research Limited Page 5
Audio
Audio Formats
This section describes how to configure the audio output section of the GXA8.
The following parameters can be adjusted;
Standard Output Format
AES.
Input/Output Formats Available Through Expansion Cards
AES (expansion card to provide 8 channel dual wire 192kHz output)
SDIF-2 output
SDIF-2 input
TDIF
ADAT
DSD (Direct Stream Digital) – output only
What is Direct Stream Digital?
DSD was invented and developed by the Sony Corporation. It is designed to remove
some of the potential artifacts introduced by the decimation filter in a conventional
analogue to PCM digital conversion process. The DSD modulator generates a
2.8224MHz bitstream per channel, which is a slightly larger bandwidth than for 24 bit
96kHz PCM audio.
AES Output Configuration
You can select single wire, dual wire or quad wire. The setting refers to the position of
consecutive samples within an audio carrier.
In single wire mode each consecutive audio sample for a given track is located within
that track. For the AES format this means that one AES cable can carry two tracks of
information.
Dual wire mode means that each consecutive audio sample is contained in adjacent
tracks. For the AES format this means that one AES cable can carry only one track of
information.
Quad wire mode means that successive audio samples rotate through four adjacent
tracks. For the AES format this means that two AES cables carry one track of
information.
In master clock mode:-
at 44.1kHz or 48kHz sample-rate, the AES output is single wire and the button is
disabled.
at 88.2kHz or 96kHz sample-rate, the AES output can be either single or dual wire.
at 176.4kHz or 192kHz sample-rate, the AES output can be either dual or quad wire.
In slave clock mode:
with an input clock of 44.1kHz or 48kHz, the AES output can be single, dual or quad
with an input clock of 88.2kHz or 96kHz, the AES output can be single or dual

GXA8 Operational Manual Rev 1.0 Audio
Genex Research Limited Page 6
SAMPLE RATE
Output
configuration
available 44.1kHz 48kHz 88.2kHz 96kHz 176.4kHz 192kHz
1-2
Tracks Single Single Single Dual Single Dual Dual Quad Dual Quad
3-4
Tracks Single Single Single Dual Single Dual Dual Quad* Dual Quad*
5-6
Tracks Single Single Single Dual* Single Dual* Dual* Dual*
NUMBER OF TRACKS
7-8
Tracks Single Single Single Dual* Single Dual* Dual* Dual*
* - only available with the AES, TDIF, ADAT or SDIF expansion card in slot 2
Bits Out and Dither
This setting truncates the output audio to the selected number of bits. Dither is added
automatically.
Available choices of bit depth are 16, 20 and 24.
Bit Split – Encode or Decode
Two different bit-split formats are used depending on whether the GXA8 is in PCM or
DSD mode. DECODE will only function on digital inputs via AES, TDIF, ADAT and
SDIF (input) cards.
PCM mode. The Paqrat®format is supported. This allows 24-bit recordings to be
made on legacy 16-bit recorders. Two channels on the recorder are required per 24-
bit audio channel. The left channel contains the first 16-bits and may be monitored.
The right channel contains the top eight bits plus a rather unpleasant tone (750Hz at
48kHz; 689Hz at 44.1kHz) at –19dBFS. The tone provides signal present
confirmation for the level meters on the recorder but should not be monitored through
any speakers.
DSD mode. Normally in DSD mode the AES outputs provide a decimated version of
the DSD signal at 44.1kHz. This is to allow back-up PCM recording for example and
may also be dithered to 20 or 16-bits. However, selecting ENCODE bit-maps two
channels (channels one and two) of DSD across eight 16-bit PCM channels (i.e., 4
AES cables). This allows stereo DSD recordings to be made on legacy 8-channel 16-
bit PCM machines. Tape based recorders may still not be suitable however as the
error correction techniques that have to be employed for digital tape will further
corrupt the DSD stream over and above any errors on the tape in the first place!
DECODE is not available for this format.
Audio Mute
The mute button mutes the audio at the outputs only (AES and any slot cards). The
PPMs will still display the input level. This allows gain levels to be set with test tones
without having to listen!
The exception is DSD mode. A “zero” bitstream in DSD is interpreted as a full scale
DC voltage which is undesirable. Therefore the audio is muted at the converters and
as a result PPM readings will be muted also. However, the PPMs may read a very
low level when muted. This is normal for the converters chips being used for DSD.

GXA8 Operational Manual Rev 1.0 Clocks
Genex Research Limited Page 7
Clocks
It is vitally important that the clock used at the point of conversion between the analogue and digital
domains is stable and accurate. Ideally the GXA8 should be the clock master wherever possible, as
the unit uses a very stable fixed crystal oscillator to generate it’s own clocks. However, operating with
the GXA8 in master mode is not always possible, so the unit provides several methods for locking to
external sources where necessary.
Lock Mode
Precision
The precision locking mode should always be selected in the first instance. The
precision mode uses a very heavily damped phase locked loop that is designed to
severely attenuate any clock jitter present on the input source. The downside is, that
if the input clock varies or drifts too much in frequency, then lock will not be possible.
Wide
Wide mode should be used when the precision mode is not capable of locking to the
external source. A more relaxed phase locked loop is selected in this mode, with less
attenuation of jitter.
Clock Source
The clock source can be either Master, external word-clock, slot one or slot two.
Master
This selects the precision quartz crystal oscillator. This is the preferred lock source.
The audio converter should always be the clock master wherever possible.
External Word Clock
This selects the word clock input BNC at the back of the unit. The frequency should
be x1 sample rate for single wire, ½ sample rate for dual-wire and ¼ sample rate for
quad-wire.
Slot One
This selects the card in slot 1 as the clock source.
Slot Two
This selects the card in slot 2 as the clock source.
Note that the DSD and SDIF cards cannot provide a clock source.
Sample Rate
The GXA8 supports the following PCM sample rates:-
44.1kHz; 48kHz; 88.2kHz; 96kHz; 176kHz; 192kHz
In addition, when locked to an external clock, the GXA8 supports all modified rates based around
44.1kHz and 48kHz (±0.1%, ±4%). The GXA8 will also lock to 32kHz. Input clock rates from 32kHz to
50kHz, plus 88.2kHz and 96kHz may be applied.
When the GXA8 is in MASTER clock mode, the sample-rate is selected pressing the sample rate button
until the desired rate is indicated.
When locked to an external clock source, the incoming clock rate will be calculated and displayed.
The WIDE or PRECISION LED will flash until the unit has obtained lock. If the incoming rate is a
“modified” rate, then the up or down arrow will also light to indicate a pull-up or pull-down rate
respectively (see note below). The sample rate button is disabled in this case. However, single, dual
or quad-wire mode can now be selected. The indicated rate will change based on the output wire
configuration. For example:-

GXA8 Operational Manual Rev 1.0 Clocks
Genex Research Limited Page 8
•A clock rate of 48kHz is connected to the clock input and detected:
In single-wire mode, a sample-rate of 48kHz will be indicated
In dual-wire mode, a sample-rate of 96kHz will be indicated
In quad-wire mode, a sample-rate of 192kHz will be indicated
In this way, the GXA8 always displays the actual sample rate rather than the external clock rate.
Note that when locked to a clock rate of 88.2kHz or 96kHz only single or dual-wire mode may be
selected.
NOTE: When either of the pull-up / pull-down LEDs are lit, the GXA8 is using a fast reacting, wide
locking RC Phase Locked Loop instead of its variable crystal oscillators. As a result, the
GXA8 may not notice if you subsequently change the incoming sample rate, particularly if you
change from a ±0.1% modified to the unmodified rate. In this case, to ensure the GXA8 locks
to the new unmodified rate using its variable crystal oscillator (which has far greater jitter
performance and thereby greater audio conversion quality), the unit should be forced to re-
lock (just cycle the unit through to master clock mode and back again).