The original, diminutive Apogee Duet was a revelation when it hit the market back in 2008. The Apogee Duet 2 ($595 direct) continues in the same vein, with even better sound quality, and a marked switch from FireWire to USB support—the latter necessary given how Apple is steadily removing FireWire ports from its latest Macs. It's not perfect, but despite its seemingly high price, it's a solid value given how great it sounds.

Design and Connectivity
The Duet 2 is made of textured silver aluminum, with a black glass front panel. It measures 6.3 by 4 by 1.3 inches (HWD), including the protruding volume knob. The knob rotates smoothly in both directions; push it in, and you'll switch between controlling input levels for the two inputs, speaker volume, and headphone volume. A headphone jack sits on the top; two would have been better. The back panel features a DC power adapter input, the breakout cable port, and a USB 2.0 port. Fortunately, the Duet 2 is bus-powered; you shouldn't need the included AC adapter unless your system pops up a warning about USB power draw, in which case the AC adapter could be used to alleviate it.

The breakout cable consists of two combination XLR and 1/4-inch inputs, and two 1/4-inch balanced outputs. It's a little less cumbersome than the white squid that shipped with the first Duet. Apogee also sells a $49 breakout box that eliminates most of the extra wiring, which is nice to have, although then you get into the question of whether a slightly larger USB interface with everything integrated would have been better or more portable than two smaller pieces.

Latency Tests and Performance

The Duet 2 records at 24-bit and at sample rates up to 192kHz, putting it on par with top-end interfaces from Avid and Universal Audio, not to mention Apogee's own, much higher-priced gear. I tested the Apogee Duet 2 with a Ivy Bridge-powered 15-inch MacBook Pro with 8GB RAM and a variety of digital audio sequencers, including Pro Tools 10, Apple Logic Pro, and MOTU Digital Performer 8. The interface worked nicely with all three, for both recording and playback. 

Playback latency from a MIDI controller was commendably short; in Logic Pro 9.1.8 in 64-bit mode, by setting the buffer to 64 samples, I could reliably achieve a resulting output latency of 2.5ms and a resulting roundtrip latency of 5.8ms. Sometimes I heard a few pops and some cut off samples with various plug-ins on my system, depending on the plug-in, even with no other tracks loaded; in this case, bumping it to 256 samples cured the audio issues, although output latency rose to 6.9ms and roundtrip to 14.5ms.

A few times, I noticed that the interface had either shut off completely, or switched back to a frozen "A" logo screen; unplugging it and plugging it back in remedied the problem in each case. But that was confusing, since the original Duet was bulletproof on FireWire, and  I was testing the Duet 2 plugged directly into the MacBook Pro (not with a USB hub).

Connection issues aside, the Duet 2 sounds incredible. In fact, the Duet 2 is actually great just as a headphone amp, for listening through higher-end open-backed and closed-back headphones for monitoring or just enjoying music. You can hear all of the detail work in Ani DiFranco's "Knuckle Down," including her fast up-and-down pick movements and the resonant sound of the acoustic guitar body. The low-end of the acoustic bass was tight, with just the right amount of finger noise on the frets. Rage Against the Machine's "Fistful of Steel," a high watermark for rock recordings from 1992, just before the loudness wars began in earnest, sounded huge, heavy, and transparent, with thunderous guitars and pristine vocal effects. Vocal recordings through a Rode NT-1A mic sounded crisp, clear, and detailed, and are a significant step up from what you get out of lower-priced interfaces like the M-Audio Fast Track.

Conclusions
All told, the Duet 2 is a beautiful sounding audio interface, even considering its high price-per-channel ratio. But the competition is catching up quickly. The new Focusrite Forte and MOTU Track 16 have the key advantage of working with both Macs and PCs. We've yet to review either, but one key downside with the Forte is that you need to have the AC adapter plugged in when recording mics with phantom power, a limitation the Apogee Duet 2 doesn't have. The Forte also only has one headphone jack like the Duet 2. The MOTU Track16, meanwhile, offers two headphone jacks in different sizes (one 1/4-inch and one 1/8-inch) and more front panel controls.

Finally, at NAMM 2013 in January, Apogee announced a slightly reworked version of the Duet 2, called the Duet for iPad/Mac; it's the same box, but with a breakout cable and internal hardware that also supports iOS devices in addition to Macs. The Duet 2 reviewed here can't be retrofitted to work with an iPad. Apogee has yet to start shipping the Duet for iPad/Mac in earnest, but all indications are that it will sound and work exactly the same as the Duet 2, aside from the addition of iPad compatibility, and will still have the same limitations; we won't know for sure until we test one, though. Whichever Duet you get, you'll be thrilled with its sound quality; just make sure you don't need the extra features the competition offers first. Finally, if you're a Reason fan, check out the Propellerhead Balance, which despite being a first for the company in terms of audio interfaces, acquits itself very well in build quality, features, and overall sonic clarity.