Apollo x8 Review: Rack Interface With HEXA Core DSP

As an Amazon Associate I earn from qualifying purchases. This write-up is based on Universal Audio’s published specifications and documentation, not hands-on testing.

The Apollo x8 is Universal Audio’s 18×24 rack-mount Thunderbolt 3 audio interface with four Unison mic preamps, two Hi-Z inputs, eight line inputs, dual optical ports, S/PDIF, word clock and HEXA Core DSP. It is built for studios that use a lot of line-level gear and outboard processing and want UAD plug-ins in real time.

See the Universal Audio Apollo x8 on Amazon. The linked listing is the Apollo x8 Gen 2 with UAD Analog Classics, the current generation.

Apollo x8 key specs

I/O	18 x 24 over Thunderbolt 3
Inputs	4 Unison mic preamps, 2 Hi-Z instrument inputs, 8 ¼” line inputs
Digital	2 optical Toslink I/O (ADAT S/MUX), RCA coaxial S/PDIF, BNC word clock
DSP	HEXA Core
Conversion	D/A rated at 130 dB dynamic range, −127 dB THD (UA figures)
Monitoring	Speaker switching, talkback, Monitor Correction by Sonarworks, up to 7.1 surround

Source: Universal Audio’s Apollo x8 page.

Unison preamps on the x8

The four mic preamps are Unison preamps, the same system used on the desktop Apollos. Loading a preamp emulation in Console changes the hardware preamp’s impedance and gain behaviour to match the original unit, so a mic responds as it would through that hardware. The emulation is part of the recorded signal. Two Hi-Z inputs also work with Unison amp emulations, so guitar and bass can be tracked through an amp model with near-zero latency while a clean signal is kept for later if the routing allows.

Because the x8 has only four of these preamps, studios that track full drum kits usually add an eight-channel ADAT preamp on one of the optical ports.

Why so many line inputs

The x8 has only four mic preamps but eight line inputs. That suits studios with outboard preamps, synths, drum machines or a summing mixer. External preamps connect at line level, so a studio with four favourite hardware preamps can keep them permanently patched, while still using the four Unison preamps for other sources.

An example studio layout

A typical x8 room might look like this:

• The four Unison preamps take vocal and instrument mics in the live room.
• Line inputs carry two hardware preamps, a stereo synth and a drum machine, all patched permanently.
• Line outputs send to a hardware compressor and a spring reverb, returning on spare line inputs for hybrid mixing.
• An eight-channel ADAT preamp on one optical port adds drum mics when a full kit is recorded.
• The monitor outputs feed main monitors, with alternate outputs on a second pair of reference speakers.

This kind of setup is where the x8 makes more sense than a desktop unit: the value is in leaving everything connected so ideas can be captured without re-patching.

HEXA Core DSP

Six DSP chips give the most real-time UAD processing in the Apollo X line alongside the x16. Large tracking sessions with Unison preamps and compression on every input, and mixing sessions with many UAD plug-ins, both benefit. UA lists more than 200 UAD titles; a starter set is included.

Digital I/O and clocking

Two optical ports allow 16 channels of ADAT at standard sample rates; S/MUX lets ADAT carry higher sample rates at reduced channel counts. Word clock on BNC lets the x8 act as clock master or follow an external clock, which matters in studios with several digital devices.

Console features

UA highlights Auto-Gain, bass management, 7.1 surround monitoring and Plug-In Scenes in Console. These help when switching between projects or when monitoring in surround. For immersive formats beyond 7.1, UA points users to the x16.

Who should consider the Apollo x8

• Studios with outboard gear and synths that need many line inputs.
• Engineers who mix with lots of UAD plug-ins.
• Rooms that need surround monitoring up to 7.1.

Who should look elsewhere

• Home producers recording one or two sources at a time; a desktop Apollo such as the Apollo x4 is easier to use.
• Studios that need eight mic preamps in one box.
• Immersive mixers working in Dolby Atmos; consider the x16.

DAW workflow: hybrid sessions

1. Create hardware insert routing in your DAW for each piece of outboard gear connected to the line outputs and inputs.
2. Use your DAW’s latency measurement for those inserts so returns stay in time.
3. Save Console sessions with projects to recall preamps and monitor settings.
4. Print hardware processing to audio before archiving a project.

Alternatives: the Apollo x4 for a desktop unit, or the Apollo x16 for sixteen line channels and immersive monitoring.

How to set up the Apollo x8

The Apollo x8 is a rack unit with a lot of I/O. So setup goes best with a plan for cables and clocking.

1. Rack it. Leave space for airflow and cable access at the back.
2. Connect Thunderbolt. Use a Thunderbolt 3 or 4 cable to your Mac or Windows computer.
3. Install UA Connect. It installs the driver, Console and plug-in licenses. Register the unit and update firmware.
4. Wire inputs. Use the four Unison preamps for mics and the eight 1/4″ line inputs for synths, outboard or other preamps.
5. Wire outputs. Connect the two monitor outs. Use the eight line outs for ALT speakers, surround or hardware sends.
6. Set clocking. If you add ADAT or S/PDIF gear, pick one master clock. BNC word clock is available too.
7. Build Console mixes. Create headphone cues for the two headphone outputs and save a Plug-In Scene.

Then test every input with a quick recording. Label cables as you go, since an x8 rack fills up fast.

Apollo x8 vs other Apollo interfaces

This table compares the Apollo x8 with nearby models, based on UA’s published specs.

Feature	Apollo x8	Apollo x4	Apollo x16	Apollo Twin X
I/O	18 x 24	12 x 18	18 x 20	10 x 6
Unison preamps	4	4	None	2
Line inputs	8 x 1/4″	Not listed separately	16 (DB-25)	Not listed separately
DSP	HEXA Core	QUAD Core	HEXA Core	DUO or QUAD
D/A dynamic range	130 dB	129 dB	133 dB	129 dB
Headphone outs	2	2	Not listed	1
Surround monitoring	Up to 7.1	Not listed	Up to 9.1.6	Not listed
Form factor	Rack	Desktop	Rack	Desktop

Put simply, the x8 keeps the x4’s preamps but adds line I/O, HEXA Core DSP and 7.1 monitoring. The x16 drops preamps in favor of 16 line channels.

Expanding with two optical ports

UA lists two optical Toslink I/O ports with ADAT S/MUX. With two eight-channel ADAT preamps, you can add 16 more mic inputs at standard sample rates. That is enough for a full drum kit plus a band.

S/MUX lets ADAT carry audio at higher sample rates, but with fewer channels per port. So check your preamp’s manual before you plan a high-rate session. In addition, set one master clock. The x8 has Dual-Crystal Clocking, according to UA, so it often makes sense as the master.

Running 7.1 surround

The eight line outputs can feed a 7.1 surround system. Choose the surround mode in Console and route each output to the right speaker. Then use Bass Management to integrate a subwoofer.

Monitor Correction can help level and balance the speakers. UA notes it requires SoundID Reference and a measurement mic. For bigger immersive formats, look at the x16, which UA lists up to 9.1.6. Our guide to Dolby Atmos mixing and mastering explains the formats.

Who the Apollo x8 is for

• Project studios that record bands and need room to grow.
• Producers with synths, drum machines and outboard gear.
• Engineers who want HEXA Core DSP for heavy tracking chains.
• Rooms that need 7.1 monitoring.

Who should skip it

• Solo creators who record one or two sources. The Twin X fits better.
• Desktop-only setups without rack space. Consider the x4.
• Mix rooms needing 16 line channels or 9.1.6. Look at the x16.
• Computers without Thunderbolt.

Pros and cons

Pros	Cons
Four Unison preamps plus eight line inputs	Rack unit, not a desktop box
HEXA Core DSP	Thunderbolt only
Two optical ports, S/PDIF and word clock	Only four mic preamps without expansion
130 dB D/A and -127 dB THD (UA figures)	Monitor Correction needs extra software and a mic
Up to 7.1 monitoring, talkback and ALT	More I/O than small studios need

Using line inputs for hardware

Eight line inputs make the x8 a good hub for gear. For example, leave synths plugged in all the time. Then record them without repatching. Likewise, use line outs and inputs as hardware inserts for compressors or EQs.

To keep inserts in time, use your DAW’s hardware insert tool. It measures round-trip delay. Also, keep levels matched between sends and returns, so you hear the gear’s effect rather than a volume change.

Tracking a band with the x8

A typical band session uses the four Unison preamps for the most important mics, such as vocal, kick, snare and bass. An ADAT preamp then handles toms and overheads. Meanwhile, the two headphone outputs feed two cue mixes.

Build those cues in Console. For instance, give the drummer more click and bass, and give the singer more vocal. If more performers need mixes, route cues through line outputs to a headphone amp. Then save the whole setup as a Plug-In Scene for next time.

Managing HEXA Core DSP

HEXA Core gives the x8 plenty of DSP. Still, a dozen heavy chains can add up. Watch Console’s DSP meter as you build a session. In addition, use lighter plug-ins for headphone reverb, and move mixing plug-ins to native versions where possible.

For full specs, see UA’s official Apollo x8 page.

Choosing Unison preamps on the x8

Each of the four Unison preamps can load a different emulation. This lets you match the preamp to the source. However, adding color everywhere can crowd a mix, so be selective.

• Vocals: A tube-style preamp such as the UA 610 adds warmth.
• Kick and bass: A punchier preamp can add weight.
• Snare: Try a clean or slightly colored setting and watch the peaks.
• Guitar DI: Use a Hi-Z input with a UAD amp plug-in for monitoring.

Because Unison is printed, choose carefully. If in doubt, record cleaner and color the sound in the mix.

Gain staging with Auto-Gain

UA’s Console includes Auto-Gain. Each performer plays at full level, and Console sets the preamp gain. This speeds up band setups, where several inputs need levels at once.

Even so, check every channel by ear. Leave headroom, because players often hit harder during a real take. Then save the session as a Plug-In Scene so the next setup starts from a good place.

Is the Apollo x8 worth it for you?

The x8 makes sense when you need preamps and a lot of line I/O in one rack. As a result, it works well as the center of a growing studio. On the other hand, small setups may not use its inputs. Count the sources you record at once and the gear you want connected. If both numbers are high, the x8 is a strong match. UA also says up to four Thunderbolt Apollos can be linked, so it can grow with you.

Using talkback and ALT speakers

Talkback lets you talk to performers through their headphones. This is essential when the band is in another room. Press the button, give directions, and release it before the take starts.

ALT switching helps you check mixes. Connect a second speaker pair to the line outputs, then switch between pairs in Console. For example, compare large monitors with small speakers. Keep levels matched, because a louder pair tends to sound better and can mislead you. In addition, combine ALT checks with Monitor Correction for a more reliable picture of your mix.

Common mistakes

• Clock conflicts. Choose one clock master for all digital devices.
• Expecting full ADAT channels at high sample rates. S/MUX reduces channels as the rate rises.
• Treating line inputs as mic inputs. Line inputs need a preamp in front of a microphone.
• Not saving Console sessions. Save Console setups with your DAW projects.
• Double monitoring. Disable DAW input monitoring when monitoring through Console.
• Two clock masters. Set one master clock when using ADAT or S/PDIF gear.
• Ignoring S/MUX channel limits. ADAT channel counts drop at higher sample rates.
• Skipping insert delay compensation. Ping hardware inserts so they stay in time.
• Skipping registration. Included plug-ins stay locked until you register the unit.
• Monitoring twice. Turn off DAW input monitoring when you monitor through Console, or you will hear a doubled sound.

Setup checklist

1. Mount the unit and connect by Thunderbolt 3.
2. Install UA Connect and drivers, then register.
3. Decide clock master and set it in Console.
4. Patch line gear and outboard to line inputs and outputs, and label channels.
5. Set up monitor outputs, alternate speakers and talkback.
6. Calibrate with Monitor Correction if mixing on this system.

Related: Thunderbolt audio interface picks, Dolby Atmos mixing and mastering and the recording hub.

Check the current price of the Universal Audio Apollo x8 on Amazon.

FAQ

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