Apollo 8 User manual

Apollo 8 Hardware Manual
Customer Service & Technical Support:
USA Toll-Free: [phone]
International: [phone]
www.uaudio.com
H I GH- R ESO L U T I O N I NTER F A C E
with Realtime UAD Processing
Manual Version 150702

Apollo 8 Hardware Manual Welcome2
A Letter from Bill Putnam Jr.
Thank you for deciding to make an Apollo High-Resolution Interface part of your music
making experience. We know that any new piece of gear requires an investment of time
and money — and our goal is to make your investment pay off. The fact that we get to
play a part in your creative process is what makes our efforts meaningful, and we thank
you for this.
In many ways, the Apollo family of audio interface products represent the best examples
of what Universal Audio has stood for over its long history; from UA’s original founding in
the 1950s by my father, through our current vision of delivering the best of both analog
and digital audio technologies.
Starting with its high-quality analog I/O, Apollo’s superior sonic performance serves as
its foundation. This is just the beginning however, as Apollo products are the only au-
dio interfaces that allow you to run UAD plug-ins in real time. Want to monitor yourself
through a Neve® console channel strip while tracking bass through a classic Fairchild or
LA-2A compressor? Or how about tracking vocals through a Studer® tape machine with
some added Lexicon® reverb?* With our growing library of more than 90 UAD plug-ins,
the choices are limitless.
At UA, we are dedicated to the idea that this powerful technology should ultimately serve
the creative process — not be a barrier. These are the very ideals my father embodied as
he invented audio equipment to solve problems in the studio. So as you begin to incorpo-
rate Apollo into your creative process, we hope that the excitement and pride that we’ve
built into it comes through. We believe Apollo will earn its way into your creative work-
flow by providing stunning fidelity, great ease-of-use, and rock-solid reliability for years to
come.
As always, please feel free to reach out to us via our website www.uaudio.com, and via
our social media channels. We look forward to hearing from you, and thank you once
again for choosing Universal Audio.
Sincerely,
Bill Putnam Jr.
*All trademarks are recognized as property of their respective owners. Individual UAD Powered Plug-Ins
sold separately.

Apollo 8 Hardware Manual Table Of Contents3
Table Of Contents
A Letter from Bill Putnam Jr. ................................................................. 2
Introduction ......................................................................................... 4
What is Apollo 8?............................................................................................... 4
Apollo 8 Features .............................................................................................. 6
About Apollo 8 Documentation............................................................................ 8
Web Documentation........................................................................................... 9
Technical Support............................................................................................ 10
Front Panel ........................................................................................ 11
Rear Panel ......................................................................................... 22
Digital I/O ....................................................................................................... 23
Analog I/O ...................................................................................................... 26
Installation & Configuration ................................................................. 29
Interconnections................................................................................. 30
Installation Notes ............................................................................................ 30
Basic Setup .................................................................................................... 31
Typical Setup .................................................................................................. 32
Advanced Setup .............................................................................................. 33
Apollo Expanded: Multi-Unit Wiring................................................................... 34
Specifications .................................................................................... 35
Block Diagram.................................................................................... 39
Troubleshooting .................................................................................. 40
Notices.............................................................................................. 41
Important Safety Information ............................................................................ 41
Warranty ......................................................................................................... 42
Maintenance ................................................................................................... 42
Repair Service ................................................................................................. 42
Tip: Click any section or page number
to jump directly to that page.

Apollo 8 Hardware Manual Introduction4
Introduction
What is Apollo 8?
Thunderbolt Audio Interface with UAD-2 Processing
Apollo 8 is an elegant update to one of the world’s most popular professional audio in-
terfaces — delivering enhanced sound with the tone, feel, and flow of analog recording.
This 18 x 24 Thunderbolt interface features powerful UAD-2 DUO or QUAD processing,
genuine UA analog design, and next-generation A/D and D/A conversion, putting class-
leading audio quality in a sleek new package.
Apollo 8 further distinguishes itself with Realtime UAD Processing and Unison™ tech-
nology, letting you record at near-zero latency through the full range of UAD plug-ins
from Neve, Studer, Manley, Lexicon, and more — including new mic preamp emulations
from Neve, API and Universal Audio.* Apollo Expanded software now allows cascading
up to four Apollos in a single system over Thunderbolt (Mac), so you can scale up your
studio as your needs grow.
Next-Generation Apollo A/D and D/A Conversion
Apollo 8 improves upon the original Apollo’s gold-standard audio quality with completely
redesigned, class-leading A/D and D/A conversion — giving you increased dynamic range
and even lower THD. This results in breathtaking clarity, depth, and accuracy in your
recordings, from tracking and overdubbing, to mixing and mastering.
Realtime UAD Plug-In Processing for Tracking, Mixing, and Mastering
While Apollo 8’s “natural” sound is very open and transparent, it can quickly deliver a
stunning range of classic analog tones and color via its Realtime UAD Processing. Avail-
able with UAD-2 DUO or QUAD processing onboard, Apollo’s DSP Acceleration allows for
recording through UAD Powered Plug-Ins — with as low as sub-2ms latency — letting
you monitor and “print” audio using classic analog emulations from Ampex, Lexicon,
Manley, Neve, Roland, SSL, Studer, and more.*
The Apollo 8’s bundled “Realtime Analog Classics Plus” suite of UAD plug-ins gives you
the UA 610-B Tube Preamp & EQ, Raw Distortion, Softube Amp Rooms, legacy LA-
2A, 1176, and Fairchild compressors, Pultec EQs, and more, so you have a rack full of
bonafide audio classics, right out of the box.
Using Apollo, UAD plug-ins are also available during mixing and mastering with a DAW,
putting UAD plug-ins (VST, RTAS, AU, AAX 64) at your disposal throughout the creative
process.
*All trademarks are recognized as property of their respective owners. Individual UAD Powered Plug-Ins
sold separately.

Apollo 8 Hardware Manual Introduction5
Four Mic Preamps with Unison™ Technology
A Universal Audio breakthrough, Apollo 8’s Unison technology gives you the tone of the
world’s most sought-after tube and solid state mic preamps — including their imped-
ance, gain stage “sweet spots,” and component-level circuit behaviors.
Based on unprecedented hardware-software integration between Apollo’s mic preamps
and its onboard UAD plug-in processing, Unison lets you record through stunning emula-
tions like the bundled UA 610-B Tube Preamp plug-in, or exclusive preamp emulations
from API and Neve.
Unison technology is further enhanced in Apollo 8 to include its front panel Hi-Z instru-
ment inputs, giving you dead-on impedance and gain matching for new stompbox mod-
els.
Apollo Expanded and Console 2.0
Thanks to Apollo Expanded software, users of Thunderbolt-equipped Apollo Twin, Apollo
8, Apollo 8p, and Apollo 16 audio interfaces can combine up to four Apollos and six
total UAD-2 devices — adding I/O and DSP as their studio grows. Apollo Expanded also
provides seamless integration with previous generation Apollos over Thunderbolt.
With Apollo 8’s Console 2.0 application — a complete re-imagining of Apollo’s original
Console software — you can take advantage of over 25 user-requested features such as
Channel Strip presets, Drag & Drop functionality, dynamically re-sizable windows, and
more.
Improved Monitoring and Workflow
Apollo 8 features a host of front-panel upgrades over the original Apollo, including Alt
Speakers, Dim, and Mono functions as well as input and output metering capabilities via
the new Meter button. These features combine with Apollo’s system scalability to make it
the new standard in professional multi-channel audio recording.
DSP Complement
Apollo 8 is available in two different configurations, which are differentiated by their
SHARC®DSP complement: Apollo 8 DUO with two DSPs, and Apollo 8 QUAD with four
DSPs. Apollo 8 DUO and QUAD have identical I/O features and functionality; the only
difference is how much UAD plug-in processing power is available for tracking and mix-
ing. Either way, you have an amazing sounding interface that can achieve the profession-
al sound quality of any era in recording history by using UAD Powered Plug-Ins.
Quite simply, Apollo 8 delivers the sound, feel, and flow of analog recording with all the
conveniences of modern digital equipment.

Apollo 8 Hardware Manual Introduction6
Apollo 8 Features
Key Features
• Next-generation Apollo A/D and D/A conversion for professional music production
• Onboard UAD-2 DUO or QUAD Core DSP allows Realtime UAD Processing — re-
cord through plug-ins from Neve, Lexicon, Studer, Marshall, Ampex, and more*
• 4 Unison™-enabled mic preamps for tracking through preamp emulations from
Neve, API, and Universal Audio*
• 18 x 24 Thunderbolt 2 audio interface (Thunderbolt 1 compatible) for Mac with
powerful Console 2.0 software control
• Cascade up to 4 Apollo interfaces and 6 UAD devices total over Thunderbolt
• Convenient front panel monitoring functions including Alt Speakers, and assign-
able Alt 2, Dim, or Mono
• Includes “Realtime Analog Classics Plus” UAD plug-in bundle with 610-B Tube
Preamp & EQ, Raw Distortion, Softube Amp Rooms, legacy LA-2A, 1176, and
Fairchild compressors, Pultec EQs, and more
• World class UA analog design, superior components, and premium build quality
Audio Interface
• Sample rates up to 192 kHz at 24-bit word length
• 18 x 24 simultaneous input/output channels
• Eight channels of analog-to-digital conversion via mic, line, or high-impedance inputs
• 14 channels of digital-to-analog conversion via:
• Eight mono line outputs
• Stereo monitor outputs
• Two stereo headphone outputs
• 10 channels of digital I/O via:
• Eight channels ADAT Optical I/O with S/MUX for high sample rates
• Two channels coaxial S/PDIF I/O with sample rate conversion
• Two Thunderbolt 2 ports facilitates daisy-chaining of other Thunderbolt devices
Microphone Preamplifiers
• Four high-resolution, ultra-transparent, digitally-controlled analog mic preamps
• Unison™ technology for deep integration with UAD preamp and pedal plug-ins
• Front panel and software control of all preamp parameters
• Switchable low cut filter, 48V phantom power, pad, polarity inversion, and stereo
linking
*All trademarks are recognized as property of their respective owners. Individual UAD Powered Plug-Ins
sold separately.

Apollo 8 Hardware Manual Introduction7
Monitoring
• Stereo monitor outputs (independent of the eight line outputs)
• Digitally-controlled analog monitor outputs maintains highest fidelity
• Front panel control of monitor levels and muting
• Two stereo headphone outputs with independent mix buses
• Independent front panel volume controls for headphone outputs
• Front panel pre-fader metering of monitor bus levels
• S/PDIF outputs can be set to mirror the monitor outputs
• Up to two alternate stereo monitor outputs selectable via front panel or Console software
• Assignable front panel monitor function switch for alternate speakers, dim, & mono
UAD-2 Inside
• DUO and QUAD models featuring two or four SHARC®processors
• Realtime UAD Processing on all analog and digital inputs
• Same features and functionality as other UAD-2 devices when used with DAW
• Can be combined with other UAD-2 devices for increased mixing DSP
• Includes UAD Powered Plug-Ins “Realtime Analog Classics Plus” bundle
• Complete UAD Powered Plug-Ins library is available at the UA online store
Software
Console application:
• Analog-style control interface for realtime monitoring and tracking
• Enables Realtime UAD Processing with UAD plug-ins
• Remote control of Apollo 8 features and functionality
• Virtual I/O for routing DAW tracks through Console
Console Recall plug-in:
• Saves Console configurations inside DAW sessions for easy recall
• Convenient access to Console’s monitor controls via DAW plug-in
• VST, RTAS, AAX 64, and Audio Units plug-in formats
UAD Meter & Control Panel application:
• Configures global UAD settings and monitors system usage
Other
• Easy firmware updates
• 1U rack-mountable form factor
• One year warranty includes parts and labor

Apollo 8 Hardware Manual Introduction8
About Apollo 8 Documentation
Documentation for all Apollo components is extensive, so instructions are separated by
areas of functionality. Each functional area has a separate manual file. An overview of
each file, and how they are accessed, is provided in this section.
Note: Extensive Web Documentation, including technical information not available
in other publications, is also available.
Apollo Manual Files
Note: All manual files are in PDF format. PDF files require a free PDF reader ap-
plication such as Preview (included with Mac OS X) or Adobe Reader.
Apollo Hardware Manuals
Each Apollo model has a unique hardware manual. The Apollo hardware manuals contain
complete hardware-related details about one specific Apollo model. Included are detailed
descriptions of all hardware features, controls, connectors, and specifications.
Note: Each hardware manual contains the unique Apollo model in the file name.
Apollo Software Manual
The Apollo Software Manual is the companion guide to the Apollo hardware manuals. It
contains detailed information about how to configure and control all Apollo software fea-
tures for all Apollo models using the Console application, Console Settings window, and
Console Recall plug-in. Refer to the Apollo Software Manual to learn how to operate the
software tools and integrate Apollo’s functionality into the DAW environment.
Note: All Apollo models have the same software manual.
UAD System Manual
The UAD System Manual is the complete operation manual for Apollo’s UAD-2 function-
ality and applies to the entire UAD-2 product family. It contains detailed information
about installing and configuring UAD devices, the UAD Meter & Control Panel applica-
tion, buying optional plug-ins at the UA online store, and more. It includes everything
about UAD except Apollo-specific information and individual UAD plug-in descriptions.
UAD Plug-Ins Manual
The features and functionality of all individual UAD Powered Plug-Ins is detailed in the
UAD Plug-Ins Manual. Refer to this document to learn about the operation, controls, and
user interface of each UAD plug-in that is developed by Universal Audio.
Direct Developer Plug-Ins
UAD Powered Plug-Ins includes plug-ins created by our Direct Developer partners. Docu-
mentation for these 3rd-party plug-ins are separate files written and provided by the
plug-in developers. The file names for these plug-in manuals are the same as the plug-in
titles.

Apollo 8 Hardware Manual Introduction9
Installed Documentation Location
All documentation is copied to the startup disk during software installation:
• Macintosh HD/Applications/Universal Audio
Accessing Installed Documentation
Any of these methods can be used to access installed documentation:
• Navigate the file system within the Mac OS X Finder
• Choose “Documentation” from the Help menu within the Console application
• Click the “View Documentation” button in the Help panel within the UAD Meter &
Control Panel application
• Manuals are also available online: www.uaudio.com/support/manuals.html
Web Documentation
UA Support Videos
Many informational videos are available online to help you get started with Apollo:
• www.uaudio.com/support/thunderbolt
Apollo Support Page
The latest technical information for Apollo is posted on the Universal Audio website. The
Apollo Thunderbolt support page contains updated, late-breaking information that is not
available in other publications. Please visit this page for the latest news:
• www.uaudio.com/support/thunderbolt
UAD Users Forum
The unofficial UAD users forum, for the exchange of tips and information, is online at:
• www.uadforum.com

Apollo 8 Hardware Manual Introduction10
Technical Support
Universal Audio provides free customer support to all registered Apollo users. Support
specialists are available to assist you via email and telephone during normal business
hours, which are from 9 AM to 5 PM, Monday through Friday, Pacific Standard Time.
Email Support
To request online support via email, click the link below for a direct link to the help
ticket form:
• https://www.uaudio.com/my/support/create/
Alternately, visit the main support page at www.uaudio.com/support, then click the blue
“Submit Support Ticket” button on the right side of the web page to create a help ticket.
Telephone Support
USA toll-free: [phone] (1-877-MY-UAUDIO)
International: [phone]
Germany, Austria, Switzerland,
France, Benelux: [phone]

Apollo 8 Hardware Manual Front Panel11
Front Panel
This section describes the features and functionality of all controls and visual elements
on the Apollo 8 front panel.
Note: All front panel functions (except the METER switch, headphone volume
knobs, and power switch) can be controlled remotely with the included Console
software application. Changes made with the front panel controls are mirrored in
the Console application, and vice versa.
Apollo 8 front panel (left portion)
(1) Hi-Z Inputs 1 & 2
The Hi-Z (high impedance) JFET direct inputs are for connecting low-level passive
devices such as electric guitar and bass instruments into channels 1 & 2 for A/D
conversion. Hi-Z input gain levels are adjusted with the Preamp control for the
associated channel.
The Hi-Z inputs have a default input impedance of 1M Ohms. The input impedance may
vary when Unison plug-ins are inserted on the channel within the Console application.
For details, see the Unison chapter in the Apollo Software Manual.
Note: Connect only ¼” unbalanced TS mono phone plugs to the Hi-Z inputs. TRS
stereo plugs cannot be used.
Automatic Input Detection
Hi-Z inputs 1 & 2 use the same A/D converter channels as the corresponding Mic 1 &
2 and Line 1 & 2 inputs. When a device is plugged into a Hi-Z input, the Mic and Line
inputs for the channel are overridden, the Mic/Line switch for the channel has no effect,
and the stereo link is severed (if active).
Important: To use Mic or Line inputs 1 or 2, its corresponding Hi-Z input must be
disconnected.
MONITOR
PREAMP
21
POWER
HEADPHONES
PAD
INPUT
+48V
Ø LINK
METER
ALT
FCN
OUT
HI-Z 1 HI-Z 2
OFF
1 2
C
0
-6
-3
-9
-12
-15
-18
-21
-27
88.2
RATE
44.1
48
176.4
96
192
HOST
CLOCK
INT
EXT
METER
IN
OUT
12345678
CLIP
0
-6
-3
-9
-12
-15
-18
-21
-27
LINE
Hi-Z
1 2
C
0
-6
-3
-9
-12
-15
-18
-21
-27
88.2
RATE
44.1
48
176.4
96
192
HOST
CLOCK
INT
EXT
METER
IN
OUT
12345678
CLIP
0
-6
-3
-9
-12
-15
-18
-21
-27
MIC
Hi-Z
INPUT
4 5 7
2 3 11
13 1716 18 19 20 22 23 24
26
25
21
12
14
1
10
6 8 9
15
1 2 3 4

Apollo 8 Hardware Manual Front Panel12
(2) Preamp Gain & Channel Select Knob
This rotary encoder with integrated switch has three functions:
Rotate – Rotating the knob adjusts the preamp gain for the selected input channel.
Press – Pressing the knob selects which preamp channel (1 – 4) is adjusted by the front
panel preamp controls.
Press+Hold – When a Unison plug-in is active in the channel’s dedicated Unison insert
within the Console application, pressing and holding the knob enters/exits Unison Gain
Stage Mode.
Each of the three functions above is explained in greater detail below.
Preamp Gain
The preamp gain of analog inputs 1 – 4 is adjusted with the rotary control. The preamp
channel to be adjusted is set with the Channel Select (press) function. The input to be
adjusted (Mic, Line, or Hi-Z) is determined by the state of the channel’s Mic/Line switch
(#4) or Hi-Z input (if connected).
Rotating the knob clockwise increases the preamp gain for the selected channel. The
available gain range for the preamp channels is 10 dB to 65 dB for the Mic, Line, and
Hi-Z inputs.
More than one full revolution of the knob is needed to move through the available range.
This feature increases the control resolution for more precise preamp gain adjustments.
Tip: To adjust signal levels for inputs 5 – 18, use the output level controls of de-
vices connected to those inputs.
Line Input Gain Bypass
By default, line inputs 1 – 4 are routed through the channel’s preamp so the line input
level can be adjusted with the Gain knob. However, line inputs 1 – 4 can be individually
set to completely bypass the channel’s preamp circuitry and instead be routed directly to
the channel’s A/D converter at a fixed reference level. This feature is set with the LINE
INPUT GAIN menu in the Hardware panel within the Console Settings window.
Tip: This feature routes the preamp channel’s line input signal directly into the
D/A converter for the purest path when additional gain is not needed (for example,
when connecting external mic preamps to preamp channel line inputs).
When the channel’s LINE INPUT GAIN menu is set to BYPASS in Console Settings:
• The Preamp Gain Indicator ring (#3) for the channel is solid green
• When the Gain knob (#2) is rotated, the ring flashes to indicate that no gain ad-
justment is occurring
• If a Unison plug-in is in the channel’s dedicated Unison insert in Console, the
Unison plug-in is bypassed

Apollo 8 Hardware Manual Front Panel13
Channel Select
Pressing the Preamp knob changes the currently selected preamp channel, which deter-
mines which input (1 – 4) is adjusted by the front panel preamp controls. A preamp
channel is selected for adjustment when its Channel Select Indicator (#11) is
illuminated.
Each time the knob is pressed, the selected preamp channel increments to the next
preamp channel. If stereo linking is active, the stereo pairs are selected.
Gain Stage Mode
Gain Stage Mode is activated by pressing and holding the Preamp knob for two seconds
when a Unison plug-in is active in the channel’s dedicated Unison insert within the
Console application. When Gain Stage Mode is active, pressing and holding the knob for
two seconds deactivates Gain Stage Mode.
Gain Stage Mode is active when the Channel Select Indicator (#11) for the currently
selected channel is flashing. In this state, pressing the Gain knob cycles through the
available gain parameters within the Unison plug-in so each gain stage in the plug-in can
be adjusted from the front panel.
Note: For complete details about Gain Stage Mode, see the Unison chapter within
the Apollo Software Manual.
(3) Preamp Gain Level & State Indicator
Preamp Gain Level Indicator
The amount of preamp gain for the currently selected channel is indicated by the illumi-
nated ring surrounding the Preamp knob.
The ring indicates relative gain levels and is not calibrated to indicate any specific dB
value. However, precise numerical dB gain values for the preamps are displayed within
the Console application.
Note: If the ring is at maximum and flashes when the Preamp knob is rotated, the
channel’s LINE input is selected and LINE INPUT GAIN is set to BYPASS. See
Line Input Gain Bypass for additional details.

Apollo 8 Hardware Manual Front Panel14
Preamp State Indicator
In addition to the channel’s relative preamp gain, the ring also indicates the current state
of the preamp channel:
Green (variable) – The preamp is in default operating mode with variable gain
Green (fixed at maximum) – LINE is selected for the channel (#4) and LINE INPUT GAIN
is set to BYPASS in the Hardware panel within the Console Settings window
Unlit – The preamp gain is set to its minimum value
Orange – A Unison plug-in is active in Console’s dedicated Unison insert for the channel.
Note: See the Unison chapter within the Apollo Software Manual for complete
details about Unison operation.
(4–9) Preamp Options
This set of six switches control the preamp options for input channels 1 – 4. Press the
switches to toggle the setting. The current state of each preamp option is indicated by
the LED within each switch. Each switch function is detailed below.
(4) Mic/Line
This switch switches between the channel’s Mic (XLR) and Line (¼”) inputs on the rear
panel combo jacks. This switch has no effect if the channel’s Hi–Z input is connected
(the Hi-Z input must be disconnected to use the Mic/Line inputs).
Note: Line inputs 1 – 4 can be set to bypass the preamp circuitry. See Line Input
Gain Bypass for additional details.
(5) Low Cut Filter
When enabled, the channel’s input signal passes through a low cut (high pass) filter. This
2nd-order coincident-pole filter has a cutoff frequency of 75 Hz with a slope of 12 dB
per octave.
The Low Cut filter affects the Mic, Line, and Hi-Z inputs. Low Cut is typically used to
eliminate rumble and other unwanted low frequencies from the input signal.
(6) Phantom Power (+48V)
When enabled, 48 volts of phantom power is supplied at the channel’s rear panel XLR
input. Most modern condenser microphones require 48V phantom power to operate. This
option can only be activated when the Mic/Line switch (#4) is set to Mic.
Caution: To avoid potential equipment damage, disable +48V phantom power on
the channel before connecting or disconnecting its XLR input.
Depending on the current configuration of the hardware and software, there may be a
delay when changing the +48V state to minimize the clicks/pops that are inherent when
engaging phantom power. The +48V LED will blink rapidly during any delay.

Apollo 8 Hardware Manual Front Panel15
(7) Pad
When enabled, the channel’s XLR input signal level is attenuated by 20 dB. Pad does
not effect the Line or Hi-Z inputs.
Pad can be used to reduce signal levels when overload distortion is present at low
preamp gain levels, such as when particularly sensitive microphones are used on loud
instruments, and/or if the A/D converter is clipping.
(8) Polarity
When enabled, the polarity (aka “phase”) of the input channel’s signal is inverted.
Polarity affects the Mic, Line, and Hi-Z inputs.
Tip: Polarity inversion can help reduce phase cancellations when more than one
microphone is used to record a single source.
(9) Stereo Link
This switch links the preamp controls of adjacent channels together (1+2 or 3+4) to
create stereo input pairs. When channels are linked as a stereo pair, any preamp control
adjustments will affect both channels of the stereo signal identically.
Note: Only the same type of inputs can be linked (Mic/Mic or Line/Line). The Hi-Z
inputs cannot be linked.
(10) Input Indicators
These indicators (MIC/LINE/HI-Z) display which input is currently active for the channel.
To select MIC or LINE, use the INPUT switch (#4). To select Hi-Z, plug a ¼” mono TS
cable into the Hi-Z input.
LINE indicator color
The color of the LINE indicator changes to reflect the state of the LINE INPUT GAIN
setting, which is configured in the Hardware panel within the Console Settings window.
White – The line input is routed through the preamp so the input gain can be adjusted.
Green – The preamp circuitry is bypassed and the line input is fixed at a reference level
of +4 dBu.
(11) Channel 1 – 4 Select Indicators
The currently selected preamp channel is indicated by the illuminated numbers above
level meters 1 – 4. When a preamp channel (or channels, when stereo linked) is
selected, its channel number is illuminated. The currently selected channel increments
when the Preamp knob (#2) is pressed.
Note: The numbers for channels 5 – 8 do not illuminate, as they cannot be se-
lected for front panel control adjustments.

Apollo 8 Hardware Manual Front Panel16
(12) Channel Level Meters
The 10-segment LED channel meters display the input or output signal peak levels for
analog channels 1 – 8. Input or output metering is selected with the METER switch
(#19), and the input/output state is shown by the METER indicators (#15).
The dB values of the meter LEDs are indicated between the meters for channels 4 and 5.
When digital clipping occurs in input (when 0 dBFS is exceeded), the red “C” (clip) LED
illuminates.
Input Channel Meters
When set to INPUT, the channel meters display the signal peak input levels for analog
channels 1 – 8 at the input to the A/D converters.
Avoid digital clipping at the channel’s A/D converter by reducing the output level of
the device connected to the channel’s input, and/or in the case of channels 1 – 4, by
reducing the preamp gain and/or engaging the Pad (#7) and readjusting gain as needed.
Output Channel Meters
When set to OUTPUT, the channel meters display the signal peak output levels for analog
channels 1 – 8 at the output of the D/A converters.
Apollo 8 front panel (right portion)
(13) HOST Indicator
The HOST indicator displays the status of the Thunderbolt connection to the host
computer system. The possible states are:
Lit – The unit is communicating with the host computer and operating normally.
Unlit – The unit is starting up or it is not recognized by the host computer. Verify
software installation and Thunderbolt connections.
Red – System error. Please contact technical support if the issue persists.
MONITOR
PREAMP
21
POWER
HEADPHONES
PAD
INPUT
+48V
Ø LINK
METER
ALT
FCN
OUT
HI-Z 1 HI-Z 2
OFF
1 2
C
0
-6
-3
-9
-12
-15
-18
-21
-27
88.2
RATE
44.1
48
176.4
96
192
HOST
CLOCK
INT
EXT
METER
IN
OUT
12345678
CLIP
0
-6
-3
-9
-12
-15
-18
-21
-27
LINE
Hi-Z
1 2
C
0
-6
-3
-9
-12
-15
-18
-21
-27
88.2
RATE
44.1
48
176.4
96
192
HOST
CLOCK
INT
EXT
METER
IN
OUT
12345678
CLIP
0
-6
-3
-9
-12
-15
-18
-21
-27
MIC
Hi-Z
INPUT
4 5 7
2 3 11
13 1716 18 19 20 22 23 24
26
25
21
12
14
1
10
6 8 9
15
1 2 3 4

Apollo 8 Hardware Manual Front Panel17
(14) CLOCK Indicators
The clock source and status are displayed with these indicators. Either internal (INT) or
external (EXT) is displayed. The clock source is set within the Console application; see
the Apollo Software Manual for details.
Internal Clock
When set to internal clock, the INT indicator is illuminated white.
External Clock
Apollo 8 can use an external clock from the Word Clock, S/PDIF, or ADAT inputs. The
EXT indicator has two possible states:
White – When set to external clock and a valid clock signal is detected at the specified
port, the EXT indicator is illuminated white and Apollo 8 is synchronized to the external
clock source.
Red – When set to external clock and a valid clock signal is NOT detected at the
specified port, the EXT indicator is illuminated red and the internal clock remains active
instead. In this situation, if/when the specified external clock becomes available, Apollo
8 switches back to the external clock, and the EXT indicator is illuminated and white.
Important: When set to use any external clock source, Apollo 8’s sample rate must
be manually set to match the sample rate of the external clock.
(15) METER Indicators
These indicators show the current state of the Channel Level Meters (#12). The current
state is changed with the METER switch (#19).
IN – When IN is illuminated, the channel meters display analog input signal levels.
OUT – When OUT is illuminated, the channel meters display analog output signals levels.
(16) Power Indicator (UA Logo)
The Universal Audio logo illuminates when the external power supply is properly
connected to the AC outlet and the power input on the rear of the unit, and the Power
switch (#26) is in the up position.
(17) Sample Rate Indicators
These indicators display the current sample rate setting for A/D and D/A conversion.
The sample rate is set within the Console application or the host DAW; see the Apollo
Software Manual for details.

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(18) Monitor Output Level Meters
The 10-segment LED meters display the signal peak output levels of the rear panel Left
& Right Monitor outputs at the output of the D/A converters. These meters are before the
Monitor Level control (pre-fader) and reflect the D/A converter levels regardless of the
current Monitor Level and Headphone Level knob settings.
The dB values of the monitor meter LEDs are indicated between the left and right
channel meters. When digital clipping occurs, the red “C” (clip) LED illuminates.
If the monitor output level clips, reduce the monitor output level within the DAW and/or
reduce the output level of individual channels feeding the monitor output bus within the
Console application.
(19) Meter Switch
This switch determines whether the Channel Level Meters (#12) are displaying input
levels or output signal levels. Pressing the switch toggles the state of the meters and the
Meter Indicators (#15).
(20) Monitor ALT Switch
When ALT monitoring is configured in the Hardware panel within the Console Settings
window (when ALT COUNT is set to a non-zero value), this switch toggles between the
main monitor outputs and the ALT 1 outputs (line outputs 1 & 2).
When the ALT switch is engaged:
• The monitor signals are routed to outputs 1 & 2 instead of the main monitor outputs
• The orange LED within the switch is illuminated
• The Monitor Level Indicator (#23) is orange instead of green
For complete details about how to configure and use the ALT monitoring features, refer to
the Apollo Software Manual.
Tip: ALT 2 outputs (line outputs 3 & 4) can be selected with the FCN switch
(#21, when configured in Console Settings) or in the Monitor column within the
Console application.

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(21) Monitor Function Switch (FCN)
This is an assignable switch that can be configured to control one of three monitoring
functions. The function of the switch is configured with the FCN SWITCH ASSIGN menu
the Hardware panel within the Console Settings window; see the Apollo Software Manual
for details.
The amber LED within the switch flashes when the monitoring function is active. The
function is toggled with the switch is pressed again. The available functions are:
ALT 2 – Selects the Alternate 2 monitor speakers. The monitor signals are routed to
outputs 3 & 4 instead of the main monitor outputs, and the Monitor Level Indicator
(#23) is amber instead of green when ALT 2 is active.
MONO – Sums the left and right channels of the stereo monitor mix into a monophonic
signal. The Monitor Level Indicator (#23) flashes when MONO is active.
DIM – Attenuates the signal level at the monitor outputs by the dB amount set in the
Control Room strip within the Console application. The Monitor Level Indicator (#23)
flashes when DIM is active.
Note: When more than one Apollo interface is connected in a multi-unit configura-
tion, the FCN switch is operable on the designated monitor unit only.
(22) Monitor Level & Mute Knob
This rotary encoder serves two functions. Rotating the knob adjusts the monitor output
level, and pressing the knob mutes the monitor outputs.
Monitor Level
Rotating the knob clockwise increases the signal level at the Left & Right Monitor
Outputs on the rear panel. If ALT monitor outputs are configured and active, this knob
controls the signal level at the ALT monitor’s line outputs.
Although this is a digital control, the Left & Right Monitor Outputs volume is attenuated
in the analog domain, after D/A conversion (digitally-controlled analog volume). This
method provides the utmost monitoring fidelity, in contrast to digital volume controls that
reduce levels by truncating the digital word length (aka “dropping bits”).

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Monitor Output Gain Bypass
By default, monitor output levels are continuously variable. However, the monitor
outputs can be set to completely bypass the monitor level circuitry and operate at a
fixed reference level. This feature is set with the MONITOR OUTPUT GAIN menu in the
Hardware panel within the Console Settings window.
Tip: This feature routes the signal directly from the D/A converters to the monitor
outputs for the purest signal path when level control is not needed (for example,
when connecting the monitor outputs to an external monitor controller).
When the MONITOR OUTPUT GAIN menu is set to BYPASS in Console Settings:
• The Monitor Level Indicator ring (#23) is solid green
• When the Monitor knob (#22) is rotated, the ring flashes to indicate that no level
adjustment is occurring
• ALT monitoring and assignable FCN switch features are unavailable
• Signals at the Monitor Outputs (#34) are output at line level (without attenuation)
Monitor Mute
Pressing the Monitor knob toggles the mute state of the signals at the Left & Right
Monitor Outputs on the rear panel. If ALT monitoring is configured in the Hardware panel
within the Console Settings window (when ALT COUNT is a non-zero value), the ALT
monitor outputs are also muted by this control.
When the monitor outs are muted, the Monitor Level Indicator ring (#23) is red.
Note: Monitor Mute does not mute the headphone outputs.