What the DSP in an Apollo does
Every Apollo has dedicated audio processors inside, SHARC chips that Universal Audio calls UAD-2 DSP. They run UAD plug-ins, UA's models of studio gear like the 1176 and LA-2A compressors, Pultec EQs, Neve and API preamps, tape machines and guitar amps. Your computer's CPU never touches that processing, and it pays off in two places.
The first is tracking. Apollos come with an app called Console, a virtual mixer that sits between the inputs and your DAW. Put a compressor and an EQ on the vocal channel in Console and the singer hears that processed sound in their headphones as they sing, with near-zero latency, whatever buffer size your DAW is set to. UA's manuals quote 1.1 milliseconds round trip at 96 kHz, through up to four of the included plug-ins. You can record the processed sound or keep the dry track and only monitor through the effects.
The second is mixing. Load UAD plug-ins in your DAW and they run on the Apollo's chips, leaving the CPU free for soft synths, samplers and native plug-ins. Back in 2012, when the first Apollo launched, that mattered a lot. Computers are much faster now, which is why the question is a fair one.
Unison is the part native plug-ins can't copy
Unison arrived in 2014 and it's the feature that's truly tied to the hardware. Put a Unison preamp plug-in, such as a Neve or API model, on an Apollo mic input and the interface physically changes its input impedance and gain staging to behave like the original circuit. The front-panel instrument inputs do the same for amp models, so a Fender Tweed Deluxe or Ampeg SVT plug-in sees your guitar or bass the way the real amp would.
A plug-in on your computer can only process audio after it's been converted, so it can't do this. UA's own FAQ lists Unison as one of the reasons to use the DSP versions. If you want to commit a preamp sound on the way in and feel it respond while you play, Unison only exists on an Apollo.
What native UADx changed
For years UAD plug-ins only ran on UA hardware. That ended in March 2022, when UA launched UAD Spark, a subscription of native plug-ins for Mac, with Windows following that September. In February 2023 UA started selling native versions outright. Buy a UAD plug-in that exists in both formats today and you get both licences, the DSP version for the Apollo and the native UADx version for your computer. UA says the two sound identical.
Native UADx plug-ins are activated through iLok, with three activations per licence and no dongle needed. Not every title has a native version, and some UAD plug-ins are still DSP only, but the big names like the 1176, LA-2A and Neve 1073 do.
That shifts the case for an Apollo. You no longer need DSP chips to mix with UA's compressors and EQs. What the DSP still gives you is near-zero-latency tracking through those models, Unison, and a lighter load on an older computer.
Solo, Duo, Quad or Hexa
UA names its DSP options by chip count, with one chip in a Solo, two in a Duo, four in a Quad and six in a Hexa. More chips don't change the sound. They change how many UAD plug-ins you can run at once. Here's what each model on this site has.
- The Apollo Solo USB has one chip, a Solo.
- The Apollo Twin USB only came as a Duo.
- The Apollo Twin MkII came as a Solo, Duo or Quad.
- The Apollo Twin X comes as a Duo or Quad.
- Every Apollo x4 is a Quad.
- The Apollo x6 and x8 racks are Hexa, in both generations.
A few rules from UA's manuals help you size it. DSP use goes up with sample rate, so you can run twice as many plug-ins at 48 kHz as at 96 kHz. Console can only use the Apollo's own chips. A UAD-2 Satellite or PCIe card adds DSP for plug-ins in your DAW, not for tracking through Console. The Apollo also spends a little DSP on its own mixer, so the meter never reads zero. And to keep latency down, every plug-in on one Console channel has to fit on a single chip, or two with UA's Channel DSP Pairing, so a long chain on one vocal can hit a limit even when the meter shows room.
In practice, Sound On Sound found a single chip enough to load a couple of Unison plug-ins for tracking. A Duo covers a singer-songwriter recording one or two sources with a preamp model and a compressor on each. A Quad earns its keep if you mix mostly on UAD plug-ins, work at high sample rates, or own DSP-only titles. Now that native versions exist, few home studios need to go out of their way for a Quad.
What to check on a used Apollo
Most used-Apollo trouble is about licences, connections and power, not the hardware.
- Plug-in licences. UAD plug-ins belong to the seller's UA account, not the box. Any Apollo can be registered as used without the seller doing anything, and UA then gives you a starter bundle of legacy plug-ins (the 1176LN, LA-2A, Pultec EQP-1A, UA 610-B, Marshall and Ampeg amps and more). The seller's purchased plug-ins come only if they submit UA's transfer form with plug-ins included, before you register it. It's their whole library or nothing, and native-only licences can't transfer. If a listing promises plug-ins, get that in writing, because UA won't step into disputes.
- Bundles and warranty. Heritage Edition and other new-unit bundles don't pass to a second owner unless transferred, and UA's warranty only covers the original buyer.
- Thunderbolt generation. The Twin MkII is a Thunderbolt 2 device. A Mac with USB-C Thunderbolt ports needs Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter, and UA says Thunderbolt 2 Apollos won't work on Windows PCs with Thunderbolt 4 or 5, even with adapters. The Twin X, x4 and Apollo X racks are Thunderbolt 3 and plug straight in. Our Thunderbolt interfaces page covers the rest.
- Windows and USB. The Solo USB and Twin USB are Windows only, with no Mac driver at all. Thunderbolt Apollos on Windows need a real Thunderbolt port, and UA calls AMD systems untested. The driver reality check explains what that means for your computer.
- Apple silicon. Current UAD software runs natively on M-series Macs, but UA's install steps have you start in Recovery and set Reduced Security with kernel extensions allowed.
- Power supply. Only the Thunderbolt Apollo Solo runs on bus power. Every model here needs its own 12 V supply, and the ratings differ. The Twin MkII and Twin USB take 1.5 A, the Solo USB 1.6 A, and the Twin X and x4 4.2 A. A listing without the original supply needs a matching one, and our bus power guide explains why that matters.
- Software and firmware. Install the current UAD software before connecting, then accept the firmware update it offers. UA warns that UAD software older than v10.0 can damage a first-generation Twin X or x4.
Who doesn't need one
If you record one source at a time, mix with native plug-ins, and your computer handles small buffers without clicks, an Apollo's DSP mostly sits idle. A good USB interface with direct monitoring will record the same performance, and you can still buy UA's compressors and EQs as native plug-ins. UA itself sells Volt, a USB line without DSP, for people in that spot.
An Apollo is also out if you're on Linux or a Windows on ARM laptop, which UA doesn't support.
An Apollo makes sense when you want to hear a preamp model, a compressor and reverb while you sing or play, and you want that sound printed on the way in. It also suits you if you already own UAD plug-ins, or you're joining a studio built around them. If that's you, a used Duo is the easy way in. Start with the Universal Audio models we cover, or browse every interface.
