Apollo x4 Review: Four Unison Preamps, QUAD 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 x4 is Universal Audio’s largest desktop Apollo: a 12×18 Thunderbolt audio interface with four Unison mic preamps, two Hi-Z instrument inputs, optical I/O and QUAD Core DSP for real-time UAD plug-ins. It sits between the two-preamp Twin X and the rack-mount x8, and suits producers who record up to four sources at once from the desktop.

See the Universal Audio Apollo x4 on Amazon. The linked listing is the Apollo x4 Gen 2 with UAD Analog Classics.

Apollo x4 key specs

I/O	12 x 18 over Thunderbolt
Inputs	4 Unison mic preamps, 2 Hi-Z instrument inputs, optical Toslink (ADAT or S/PDIF)
DSP	QUAD Core
Conversion	D/A rated at 129 dB dynamic range (UA figure)
Monitoring	Monitor controller with alternate speakers, talkback, Apollo Monitor Correction by Sonarworks
Connection	Thunderbolt 3 or Thunderbolt 4 controller, depending on unit

Source: Universal Audio’s Apollo x4 page.

Four preamps on the desktop

Four preamps cover a singer and guitarist with two mics each, a small drum setup (kick, snare and two overheads), or a two-host podcast with two spare inputs. All four are Unison preamps, so each can load a different preamp emulation: a Neve-style preamp on the vocal and an API-style one on the guitar amp, for example. Each emulation is part of the recorded input path.

Example sessions

• Singer-songwriter with a band feel: vocal mic on input 1, two mics on an acoustic guitar on inputs 2 and 3, and a DI from a bass or keyboard on a Hi-Z input. Everything goes down in one take with separate tracks.
• Small drum recording: kick, snare and a pair of overheads on the four preamps. Add an ADAT preamp on the optical input when you want toms and room mics.
• Producer desk: a vocal mic and a guitar amp mic on two preamps, a stereo synth on the other two, and Console handling headphone mixes for a guest artist.

The common thread is that the x4 lets a small room work like a larger one without moving to a rack. The monitor knob, talkback and speaker switching stay within reach, which matters when you are both engineer and performer.

QUAD Core DSP

Four DSP chips give room for a Unison preamp plus compression and EQ on several inputs at the same time, with near-zero latency monitoring through UA’s Console. They also run UAD plug-ins during mixing inside DAWs that support VST, AU or AAX. Heavier plug-ins use more DSP, so watch the meter in Console.

Thunderbolt 3 vs Thunderbolt 4 units

UA says that during a transition period the x4 Gen 2 ships with either a Thunderbolt 3 or a Thunderbolt 4 controller. Audio performance, latency and features are the same, but host requirements differ: units with Thunderbolt 4 need an Apple silicon Mac, an Intel Mac on a recent macOS, or a Windows PC with a Thunderbolt 4 port. Check your computer against UA’s current requirements before buying.

Monitor control and correction

The x4 includes speaker switching, talkback, and Apollo Monitor Correction by Sonarworks for monitors and headphones. Correction can make an untreated room more trustworthy, but acoustic treatment and monitor placement still matter.

Expansion

The optical port adds eight channels from an ADAT preamp, and up to four Thunderbolt Apollos can be linked, controlled from the x4 on the desk.

Who should consider the Apollo x4

• Producers recording up to four sources at once.
• Small studios that want desktop control rather than a rack unit.
• Users who mix with UAD plug-ins and want more DSP than the Twin X.

Who should look elsewhere

• Solo artists who never record more than two sources; see the Apollo Twin X or Apollo Solo.
• Studios needing eight preamps or more line I/O, which is the territory of rack-mount Apollos.
• Computers without a compatible Thunderbolt port.

DAW workflow: four-mic session

1. Name inputs in Console and save a Console session alongside the DAW project.
2. Monitor each player with their own headphone mix using Console’s cue sends.
3. Record dry and monitor through Console effects, or print a Unison preamp as part of the tone.
4. After tracking, raise the DAW buffer and use UAD plug-ins for mixing on the QUAD Core DSP.

Alternatives: the Apollo Twin X for two preamps, or a rack-mount Apollo x8 for more line I/O.

How to set up the Apollo x4

Getting the Apollo x4 running takes about the same steps as any Apollo. Follow them in order for a smooth first session.

1. Check your port. UA lists Thunderbolt 3 and 4 support on Mac, including Apple silicon and Intel, and on Windows.
2. Connect power and Thunderbolt. Plug in the power supply, then the Thunderbolt cable.
3. Install UA Connect. It installs the driver, Console and plug-in licenses.
4. Register and update. Register the unit so your bundle unlocks, then update firmware.
5. Select the Apollo in your DAW. Set it as the input and output device.
6. Build your Console mix. Assign Unison preamps, set gain and create headphone mixes.
7. Connect monitors. Use the two monitor outs. Add a second speaker pair on the ALT line outputs if you have one.

Then record a short test take on each input. That confirms routing before a real session starts.

Apollo x4 vs other Apollo interfaces

The table compares the Apollo x4 with nearby models, using UA’s published figures. It shows where the extra preamps and outputs fit.

Feature	Apollo x4	Apollo Twin X	Apollo x8	Apollo Solo
I/O	12 x 18	10 x 6	18 x 24	2 x 4
Unison preamps	4	2	4	2
Hi-Z inputs	2	1	2	1
DSP	QUAD Core	DUO or QUAD	HEXA Core	SOLO Core
Headphone outs	2	1	2	1
Optical	Toslink I/O	Input	2 x Toslink I/O	No
Form factor	Desktop	Desktop	Rack	Desktop

In short, the x4 doubles the Twin X’s preamps and headphone outputs. Meanwhile, the x8 adds HEXA Core DSP and more line I/O in a rack format.

Running two headphone mixes

Two headphone outputs make duets and lessons easier. Each performer can get a separate mix. Console’s cue sends let you build these mixes from inputs and playback.

1. Open the cue section in Console and pick a headphone output.
2. Raise each input’s cue send for that performer.
3. Add a little playback and reverb to taste.
4. Repeat for the second headphone output.

Ask each performer what they want to hear more of. Singers often want more of their voice, while guitarists may want more drums.

Using the optical port for more inputs

UA lists optical Toslink I/O that works as ADAT or S/PDIF. With an ADAT preamp, you can add eight more mic inputs at standard sample rates. That turns the x4 into a small drum-tracking rig.

First, connect optical cables both ways. Next, choose ADAT in Console. Then set one device as the clock master, usually the Apollo. Finally, check for clicks before recording, since they point to clock problems.

Who the Apollo x4 is for

• Home studios that record up to four mics at once.
• Duos who need two separate headphone mixes.
• Producers who want QUAD Core DSP on the desk.
• Mixers who want ALT speakers, talkback and Monitor Correction.

Who should skip it

• Solo artists who record one source. The Solo or Twin X costs less space.
• Studios that need rack mounting and lots of line I/O. Consider the x8.
• Computers without Thunderbolt.
• Anyone who never plans to use UAD plug-ins.

Pros and cons

Pros	Cons
Four Unison preamps on a desktop unit	Thunderbolt only
Two headphone outputs	Desktop size, not rack-mount
QUAD Core DSP	Heavy chains on four inputs can use up DSP
Optical I/O for expansion	Monitor Correction needs extra software and a mic
129 dB D/A (UA figure), talkback and ALT outs	Needs its own power supply

Auto-Gain and Plug-In Scenes

UA’s Console now includes Auto-Gain. Each performer plays at full level, and Console sets the preamp gain. That helps when you’re tracking several people at once.

Plug-In Scenes save Console setups. For instance, store one scene for vocals and another for a full band. As a result, you can switch session types quickly. Still, check gain by ear afterwards, because performers often get louder during real takes.

Setting up Bass Management

If you use a subwoofer, Bass Management helps integrate it. The feature handles the crossover between your speakers and the sub. Set it up in Console, then check the low end with music you know well. Also, combine it with Monitor Correction for a more even response in an untreated room.

Growing beyond the x4

UA says up to four Thunderbolt Apollos can be linked. Dante is also available through the Apollo x16D. So the x4 can stay on the desk while a rack unit adds inputs later. For full specs, see UA’s official Apollo x4 page.

Choosing Unison preamps for a four-mic session

With four Unison preamps, you can give each source its own character. However, too much color on every channel can make a mix muddy. Start simple and add color where it helps.

• Lead vocal: A tube-style preamp such as the UA 610 adds warmth.
• Acoustic guitar: A cleaner preamp keeps string detail.
• Kick or bass amp: A punchier preamp can add weight, but watch the gain.
• Room mic: Try a colored preamp here, since room tracks often benefit from character.

Remember that Unison changes are recorded. So, if you are unsure, keep a cleaner setting and add plug-ins in the mix.

Recording guitar through the Hi-Z inputs

The x4 has two Hi-Z inputs, so two guitarists can plug in directly. Alternatively, one player can record bass and guitar without repatching. Load a UAD amp plug-in in Console to monitor an amp tone with no audible latency.

Next, decide whether to print the amp sound. Many producers record the amp tone and a clean DI on separate tracks. That way, they can re-amp later if the tone doesn’t fit the mix.

Managing DSP across four inputs

QUAD Core DSP covers a lot, but four full chains add up. Console shows DSP use, so watch it while you build a session. If it gets high, use lighter plug-ins for headphone reverb.

In addition, move mixing plug-ins to native versions where you can. That leaves DSP free for tracking, which is where realtime processing matters most. Linking another Apollo also adds DSP for mixing.

Using talkback and ALT speakers

Talkback lets you speak to performers through their headphones. This matters when the performer is in another room. Press the talkback button, give directions, then release it before the take.

ALT speaker switching is just as useful. Connect a second pair of speakers to the ALT line outputs. Then switch between pairs in Console to hear how a mix translates. For example, compare full-range monitors against small speakers. Problems that hide on one pair often stand out on the other.

Also, keep both pairs at matched levels. Otherwise, the louder pair will usually sound better, and that can mislead you.

Is the Apollo x4 right for you?

The Apollo x4 sits in a useful middle spot. It gives you four preamps and two headphone mixes without a rack. As a result, it suits small studios that record more than one person. On the other hand, solo creators may not need the extra inputs, and big studios may want the x8. Think about how many sources you record at once, now and in the future. If the answer is three or four, the x4 is a strong fit. For more options, compare our best Thunderbolt audio interfaces roundup.

Common mistakes

• Not checking the Thunderbolt controller version. Host requirements differ between Thunderbolt 3 and 4 units.
• Using all four preamps at high gain with Unison saturation. Emulations react to level; too hot sounds distorted.
• Printing reverb. Monitor reverb through Console auxes rather than recording it.
• Double monitoring. Disable DAW input monitoring when Console is monitoring.
• Ignoring phase on multi-mic sources. Check polarity between mics on the same source.
• Monitoring twice. Leaving DAW input monitoring on while using Console causes a doubled sound.
• One headphone mix for two players. Use both outputs with separate cue mixes.
• Clock conflicts with ADAT gear. Set one master clock to avoid clicks.
• Skipping registration. Included plug-ins stay locked until you register.

Setup checklist

1. Confirm your computer meets UA’s Thunderbolt requirements.
2. Install UA Connect and drivers, register the unit.
3. Open Console and name each input.
4. Load Unison preamps and set gain per source.
5. Build headphone mixes and set up talkback.
6. Select the Apollo in your DAW and record a test of every input.

Further reading: Thunderbolt audio interface picks, what a mic preamp does, and the recording hub.

Check the current price of the Universal Audio Apollo x4 on Amazon.

FAQ

When your multitrack session is mixed, our stem mastering can finish it from grouped stems. That gives more control than a single stereo file.