When I got my new Apple Titanium PowerBook G4, my goal was to put together a portable multitrack recording rig that would run on battery power, weigh

When I got my new Apple Titanium PowerBook G4, my goal was to put together a portable multitrack recording rig that would run on battery power, weigh less than 30 pounds (including a MIDI keyboard), and fit into a small shoulder bag. Consequently, I was more than a little excited to get my hands on the Metric Halo Mobile I/O 2882, a multichannel audio interface that's optimized for mobile use. I was already a fan of Metric Halo's two software products, SpectraFoo and ChannelStrip, and I had high expectations for the company's first foray into the competitive arena of computer-audio interfaces.

The Mobile I/O comes in two flavors: the non-DSP model and, for $700 more, the +DSP model. The +DSP box has an extra digital signal-processing chip that will eventually host native effects and dynamics plug-ins. Because the software is still in development, however, the two units are functionally identical.


From the outside, the two models are also physically identical, housed in a sturdy 1U enclosure with rounded edges. Because the 2882 is a bit narrower and deeper than most rackmount audio interfaces, it fits perfectly beneath a laptop computer such as the PowerBook. If you choose to mount the 2882 in a rack, it comes with extension rack ears that bring it out to the standard 19-inch rack width and provide holes for mounting it.

The included MIO Console software controls nearly every function of the Mobile I/O by means of the FireWire bus. Thus, the 2882's front panel is almost completely free of controls, leaving plenty of room for indicator LEDs (see Fig. 1). In fact, the only front-panel controls are two tiny buttons that affect the stereo headphone output, a ¼-inch jack directly to their right. The Mute button quickly and conveniently kills the headphone signal, and the Dim button attenuates it by -18 dB. I prefer having total control from the computer, so the lack of front-panel controls isn't a problem.

What remains on the front panel are eight 10-segment LED meters for input, eight more for output, and four groups of green LEDs. One group shows the selected sample rate (44.1, 48, 88.2 or 96 kHz), and another indicates the active clock source. Status is shown by LEDs labeled Power, Phantom, FireWire, and Locked (which lights when the 2882 is locked to the clock source). Another group of LEDs specify which digital I/O is selected (AES/EBU or S/PDIF), and another Locked LED tells you whether the unit is successfully slaved to whichever of the two stereo digital inputs is selected. I appreciate having so much information displayed, but I wish the LEDs weren't so close together — it can be difficult to tell which one is illuminated, especially when the unit is viewed from an angle.


The Mobile I/O's rear panel is crowded with I/O options (see Fig. 2). The eight analog inputs are four locking female XLR jacks and four balanced ¼-inch jacks, all of which can handle balanced or unbalanced signals. Signals at either set of inputs are routed through the 2882's preamps and 24-bit, 96 kHz A/D converters. Alongside the inputs are eight analog outputs on ¼-inch TRS jacks, whose signals come straight from 24-bit, 96 kHz D/A converters.

The digital I/O section includes ins and outs for word clock on BNC connectors, eight channels of ADAT Lightpipe, coaxial S/PDIF on RCA jacks, and AES/EBU on XLRs. Also on the rear panel are two FireWire ports and a DC jack for the external lump-in-the-line power supply. According to the User Manual, the Mobile I/O can run off any DC source, from 9V to 30V, that supplies at least 12W of power to either the FireWire or DC jacks. That means a FireWire connection from a laptop computer is sufficient to power the 2882 from its internal battery. Goodbye, power cords!

ASIO is the only way the Mobile I/O can communicate with pre — OS X applications, so if you're still working in OS 9 (like me), make sure your audio programs support ASIO. Driver updates are available on Metric Halo's web site. Downloads from the site also update the controlling software and the 2882's firmware, adding new features to their functionality. That's a very good thing, considering that many expected features either still aren't available or still have bugs.


MIO Console, which at this writing is available only for the Macintosh, is the software for controlling all the Mobile I/O's parameters (except the headphone's Mute and Dim controls, which aren't yet operational). MIO Console is a comprehensive control panel with extensive functionality.

The main benefit of controlling the Mobile I/O's functions with software (as opposed to real knobs and switches) is that you can save and recall all the input, output, mixing, and routing parameters, either as individual parameter presets or as global console snapshots. That lets you create templates for the various ways you might use the interface. Factory defaults for each savable parameter let you quickly return the 2882 (or one input channel, for example) to a “zeroed” state.

MIO Console consists of three main panels — Analog I/O Control, Mixer, and Mix/Output Routing — which you access with the panel selector bar at the top of the window (see Fig. 3). The Analog I/O Control panel provides remote control for all eight analog inputs and outputs. In addition to the pop-up menu for saving and recalling channel-strip presets, the Analog Input section offers controls for each channel's phantom power, trim (with a 42.5 dB range), and level (+4 dBu line, -10 dBV line, instrument, mic, or -20 dB mic pad). In addition, each channel has a PPM-style meter that exactly mirrors the respective meter on the hardware unit. You can also link channels in odd-even stereo pairs.

To the right of the Analog Input section are the input meters for the eight ADAT inputs and two stereo digital pairs, and then a knob (labeled Cans) for setting and monitoring headphone level. Farther to the right are pop-up menus for various system functions. The Digital Input Sample Rate Conversion (DI SRC) button determines whether the incoming AES/EBU or S/PDIF signal is converted to the selected sample rate on the fly. That can come in handy if, for example, you're transferring audio from a 48 kHz DAT into an existing 96 kHz DAW project.

Analog Output contains most of the same controls as the Analog Input section. The most notable difference is that the only two options for level are +4 dBu line and -10 dBV line. Next to that section are meters for ADAT and stereo digital outputs.

Clicking the Mixer button in the selector bar changes only the bottom half of MIO Console's window, which becomes a fully configurable mixing interface with a master fader and as many as 18 input channels visible at the same time. If you need them, you can access 18 more input channels by means of a scroll bar. Each mixer channel has prefader metering, a fader for Level control, a Solo button, a Mute button, and a pan knob if it's a mono channel in a stereo mix. I was disappointed that I couldn't use MIDI to control the mixer functions.

Tabs across the top of the window let you select which mix you want to control. Control-clicking on a tab reveals a pop-up menu for copying, pasting, saving, or recalling mix configurations. Sixteen discrete mono or eight stereo mixes are available, so you can route audio from any of the 18 hardware inputs and 18 DAW buses into any mix in any way you'd like. That lets you set up multiple mixes for different headphone feeds, “stem-based” mixing, or any other multichannel routing scenario. Such a scheme is ideal for monitoring, because the Mobile I/O is capable of near-zero latency, virtually eliminating the need for an outboard mixer.

MIO Console's third panel is the Mix/Output Routing panel; it contains a pop-up menu for Matrix presets and another for Patchbay presets. The Output Patchbay section lets you select what appears at each of the 22 physical outputs (including the headphones). You have three sets of options for internally routing signals to the outputs: from any of the 16 MIO mix outputs, from any of the hardware's 18 physical inputs (for direct hardware patch-through with minimum latency), or from any of the 18 buses streaming from your DAW software through ASIO. The versatility of the patch bay is most impressive and powerful, allowing you to use the Mobile I/O as a DAW interface, a DAW-independent A/D/A converter, or a standalone mixer.

The Routing Matrix is a grid with inputs on the x-axis and mix buses on the y-axis. Clicking at the intersection of an input column and a mix row activates that input in that particular mix; your choice is reflected in the Mixer panel by a fader appearing with the appropriate label on it. That provides a convenient visual interface for streamlining your mixes so that they contain only the inputs you're currently using. You can save various configurations for different routing scenarios.


When I compared the 2882's preamps to my Focusrite Green 1 Dual Mic Pre, they stacked up pretty nicely, especially considering that the Mobile I/O costs about a third as much per channel as the Focusrite. Recording percussion through an Oktava MC012, the Focusrite had a touch more clarity on high frequencies and a little more roundness on low frequencies, but the difference was very slight. For both male and female vocals through a Shure Beta 58 and an Electro-Voice RE20, I could hardly tell the difference between the two devices, though the 2882 had a little less sibilance. I ran an RCA 77-DX ribbon mic through the preamp to test the noise floor, which also sounded comparable to that of the Focusrite.

The 2882's biggest stumbling block was its inability to deliver a clean signal through the Lightpipe inputs. I tried to transfer eight tracks from an ADAT XT20 using an optical cable, and I heard nothing but grunge and grime in both MOTU Digital Performer and BIAS Peak. The status LEDs told me that the unit was synced to the ADAT, but it sounded as if there were a clocking issue. Switching to my MOTU 2408, everything sounded fine. Online discussions (see the sidebar “Mobile Forum”) informed me that I'm not the only one who's had trouble with the ADAT inputs, though the outputs work perfectly.

An even more serious glitch is that every so often, the audio outputs (including the headphones) went silent. The meters bounced happily along as if nothing had happened, but the only way to get audio back into my speakers or phones was by cycling power on the Mobile I/O. Metric Halo promises that a fix for both problems is forthcoming, but such problems are bad news for current customers.


The prospect of running the Mobile I/O from my PowerBook G4's internal battery using the FireWire bus was extremely attractive to me because I could record anywhere without being tied to AC power. Using Digital Performer, Propellerhead Reason, and a Midiman Oxygen 8 keyboard (which can be powered by the laptop's USB bus), I could theoretically have a full MIDI and audio studio that still weighed less than my goal of 30 pounds.

Unfortunately, the backlight on the PowerBook G4/667's display automatically turns itself off if there's too much strain from powering external devices. It is a known Mac issue that Apple is addressing for newer PowerBooks, but for me and a lot of other people, the laptop's battery can power either the keyboard or the Mobile I/O, but not both. I also experienced relatively fast battery drainage running the Mobile I/O from the FireWire bus — it gave me less than two hours of use.

PowerBook battery problems aside, the 2882's overall performance in remote situations was quite good. I took it to the Ex'pression Center for New Media, where ten channels of external Studer preamplification fed the analog and AES/EBU inputs for recording drum, bass, guitar, vocal, piano, trumpet, and clarinet tracks. Every now and then I heard a little digital noise on the incoming AES/EBU tracks, but reselecting the sample rate in Digital Performer or in MIO Console got rid of it. MIO Console's routing functions were especially handy for tracking and overdubbing.


The Mobile I/O 2882 has great potential to be a powerful and versatile audio interface. In combination with the MIO Console software, its flexibility and routing capabilities are extraordinary. It offers plenty of I/O, and the ability to plug a microphone or guitar directly into the 2882 eliminates the need for external preamps or DIs. Unfortunately, it has a few significant problems.

Although the Mobile I/O's analog output sounds great, its digital input can be undependable. The 2882 is easy to use, but only when it works as it should. It offers much more functionality than its price might suggest, but functionality doesn't mean much when your playback session comes to a grinding halt. As of this writing, the 2882 has some serious bugs, and until those bugs are squashed, it remains a work in progress.

Eli Crewsused the Mobile I/O to sample his eight-month-old son's toys for a drum beat for his band The Loins, a duo with wife Beth Lisick.

Mobile I/O 2882 Specifications

Analog Audio Inputs(4) balanced XLR; (4) balanced ¼" TRSAnalog Audio Outputs(8) balanced ¼" TRSDigital Audio I/O8-channel ADAT Lightpipe; stereo AES/EBU; stereo S/PDIFWord Clock1× and 256× I/O on BNCPreamplification(8) remote-controllable preamps with 40 dB gain; switchable -20 dB pad; switchable 48V phantom powerWord Length24-bitSample Rates44.1, 48, 88.2, 96 kHzDynamic Range110 dB (A/D); 120 dB (D/A)Computer/Drive Connectivity(2) IEEE 1394 FireWire ports (400 Mbps)Power(1) 9V-30V, 15W DC power jack; (1) 24V, 48W external power supplyDimensions14" (L) × 2" (H) × 11" (D)Weight7.5 lb.


To learn more about why some of the software functions are either spotty or missing in action (such as the Preferences dialog box), I started lurking on the Mobile I/O discussion group ( The user forum is the best technical support group I've ever encountered, hands down. Not only is it filled with incredibly helpful, intelligent, and insightful information regarding the Mobile I/O and related issues and products, but much of that information is from the head engineer of Metric Halo, B.J. Buchalter.

It's quite encouraging when the guy in charge of making sure the product works right takes the time to address his customers' concerns in a setting as intimate and informal as an e-mail discussion group. He is the first to admit that some of the features of the 2882 and MIO Console aren't quite up to speed yet, but he assures us that his team is working hard on those issues. Since I received the unit for review two months ago, I have already downloaded two software updates, the latest of which includes drivers for OS X 10.2. Early reports say that the Mobile I/O integrates with OS X quite well. In addition, Metric Halo will soon release a no-frills, OS X — only recording application.


Metric Halo

Mobile I/O 2882
audio interface
+DSP model $2,195


PROS: Transparent sound. FireWire-bus power. Flexible mixing and routing functions. Remotely upgradable. Excellent customer support.

CONS: Announced features still unavailable. No Windows drivers. Unstable ADAT inputs. Intermittent AES/EBU input noise. Audio randomly drops out until power is cycled. Mixer functions not MIDI controllable.


Metric Halo
tel. (888) 638-4527 or (845) 831-8600