Review: MOTU 1248, 16A, and 8M AVB Interfaces

Powerful Interface and Networking Options
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Just before the flip of the millennium, MOTU launched its first scalable audio interface system with the release of the PCI-324 card and accompanying 2408 interface. Eventually, the company expanded to a family of audio interfaces with different I/O capabilities, up to three of which could be connected to the card. Now MOTU has recast this concept with their new AVB interfaces.

But this new family of devices is more than MOTU’s newest audio interface system. It epitomizes the latest in Ethernet-based audio networking technology and an emerging genre of interfaces with cross-platform software that incorporate full, large-scale mixing with comprehensive routing. All of this is in addition to multichannel interfacing to host software that runs on your computer. There’s a whole lot crammed into these boxes.

For this review, MOTU sent me three interfaces: the flagship 1248, the 16A, and the 8M, as well as the AVB switch that is required to use three or more interfaces.

Other than the portable UltraLite AVB, MOTU’s AVB interfaces come as 1U rackmount packages with all-metal chassis. It is clear that this equipment is built for professional use. Quarter-inch instrument inputs and headphone jacks are the only connectors appearing on the front panels. This keeps a clean look, but can be slightly inconvenient if you use one or more interfaces as a stage box in live performance.

The front panels feature high-res displays with meters to show input and output levels. When lots of channels are in use, the biggest concern is confirming they are all working at levels that are within bounds; these displays fulfill that purpose very well.

The concept behind this kind of system is that each interface has a different selection of input and output types and quantities, allowing you to pick and choose according to your situation. The chart on pages 50 and 51 gives a summary of the configurations of each of the interfaces currently in MOTU’s AVB family.


Fig. 2. With eight mic/line inputs on combo jacks, the MOTU 8M can support a wide range of input configurations. WHAT’S IN THE BOX?

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The 1248 is the flagship of the line, an I/O grab-bag in the spirit of the 2408 and its successors, with four mic preamps and a pair of instrument inputs, with eight balanced line inputs and 12 outputs on TRS jacks (see Figure 1). For digital I/O there are two sets of ADAT optical I/O and S/PDIF in and out. The 8M, by contrast, offers eight mic/line inputs on combo jacks, eight balanced TRS outputs, and two sets of ADAT I/O (see Figure 2).

Fig. 3. The MOT U 16A offers plenty of balanced analog I/O for studios with a majority of line-level sources. The 16A is ideal for those who, like me, have a substantial quantity of outboard gear or synthesizers (see Figure 3). It sports 16 balanced line inputs and outputs on TRS jacks, plus the same digital I/O and interfacing package as the 8M.

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The other MOTU interfaces offer their own specialized I/O selections. The 112D is entirely digital I/O with AES/EBU, ADAT optical, and MADI. The Monitor 8 provides up to eight stereo mixes (derived from eight analog inputs, 16 channels of ADAT optical, and up to 64 channels from other devices or track playback from the computer) that can feed six headphone amps. There’s even a new AVB version of MOTU’s popular UltraLite portable interface. All of the interfaces support sample rates up to 192 kHz.

The MOTU AVB interfaces can connect to a computer in three different ways. Thunderbolt will be your best bet, given its impressive bandwidth, if you have a Mac equipped with it. Each interface also has a USB 2.0 port capable of carrying 64 channels in each direction—currently the only option for Windows users. I used both USB and Thunderbolt to connect the interfaces to my Mac Pro and had no issues with either; everything was smooth and easy. The third method is to connect directly to an Ethernet port on a recent Mac that supports AVB. (According to MOTU, any Mac with a Thunderbolt port running OS X 10.10 Yosemite will support AVB Ethernet.)


The ADAT optical inputs on the interfaces let you expand the system with non-AVB-compliant devices that have ADAT outputs. I added eight mic inputs without using any of the interfaces’ analog connections by connecting the ADAT output of my Presonus Digimax D8 to a MOTU ADAT input.

Not everyone will need multiple interfaces, of course. A 1248 or an UltraLite AVB will make a fine interface on its own, and you can always hook up another MOTU AVB interface to accommodate a larger project.

Fig. 4. If you plan to daisy-chain three or more AVB devices, you will need to add the MOTU AVB Switch to your system. A second MOTU AVB interface can be daisychained via AVB, but when you get past two devices, an AVB switch is needed. MOTU’s AVB switch allows up to five interfaces to be connected and provides a port for bridging to a standard Ethernet network without compromising AVB functionality (see Figure 4).

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All of MOTU’s AVB interfaces are controlled and configured using a Web application that will run on any standard browser. This means the interfaces can be controlled from a Mac or Windows computer, an iPad or other tablet computer, or even, in theory, a smartphone (though in practice, the small screen size would be a serious challenge). The Web app is logically laid out and not difficult to use, once you have your head around how the system works.



Most of the interfaces include full 48-channel mixing, with panning, dynamics, British-flavored EQ, solo, and mute on each channel. Mix buses have an LA2A leveler emulation. The mixing has extremely low latency, but overdubbing requires playback of existing tracks, which reintroduces latency through the DAW as a potential issue (with the same solution as usual: select a small buffer size while recording).

But MOTU has optimized AVB latency. The AVB standard defines a maximum latency of 2 ms for up to seven “hops” through switches with a 100MB Ethernet connection. The MOTU AVB devices use Gigabit Ethernet and clever engineering to achieve a fixed latency over seven hops of less than a millisecond point-to-point in the network at a 48kHz sample rate, including the combined contributions of network, interface, and processor. That’s tight.

To try working with the mixer alone, I used the 1248 for a rehearsal of a band in my studio. I connected a pair of line outputs to two compact, powered P.A. speakers, and the only difference from using a traditional mixer was the lack of physical knobs, buttons, and faders, which was not even an issue in that context. Currently, there are no control surfaces that work over AVB, but MOTU is in conversation with control surface manufacturers.



Given how long MOTU has been making interfaces, one would expect the AVB family to sound excellent, and they do. MOTU has had mic preamps in previous interfaces, but has never been known as a mic preamp manufacturer, so I was curious about the onboard mic pre’s in these devices. One concern was my affinity for using light analog compression while recording, especially with drums. That’s not really possible when using mic preamps onboard an interface. How would recording without analog compression work out?

Each mic input on the 1248 offers +48V phantom power, a 20dB pad, and a polarity reversal switch. In addition to control for these features in the Web app, the 1248 supplies front-panel switches for the phantom power and pad. For loud sources like drums, I found myself engaging the pad on more channels than I usually do with my outboard mic pre’s, but that posed no problem.

The 8M’s mic inputs are a little different from those on the 1248. For a start, they are on combo jacks instead of XLRs, and accept instrument- or line-level signals as well as mic signals. They also have two features aimed at addressing my analog compression concerns. The first is VLimit, a hardware limiter on each mic input that allows signals to go up to 9 dB above 0 dBFS without clipping. The second is SoftClip, a compressor that kicks in before 0 dBFS.

I often engineer sessions on which I also play drums, which makes it harder to set levels precisely for the kit. I tend to be conservative about levels to avoid trouble, but sometimes a take will have moments where I play with a bit more enthusiasm than during my level-test recordings. I made extensive use of VLimit to compensate for this during recent tracking sessions for Reconnaissance Fly’s second album. While there were only a few times limiting engaged, it worked well in preventing clipping without imposing any significant sonic penalty. (You can always hear limiting; it’s just a matter of how objectionable the sound is.)

Other sources I recorded through the mic preamps included steel-string acoustic guitars, electric guitar amps, woodwinds, vocals, and vibraphone. The sound of the preamps is clean and clear, essentially uncolored, but not lifeless. I like their sound and am entirely happy making records with them. There was plenty of gain for both mic and line inputs, which was easily adjusted in the Web app. They easily beat the pants off the mic pre’s in most small console and inexpensive outboard channel strips. I also made use of the instrument inputs for bass and electric guitar and was pleased to hear they did not lose body and punch the way many DIs do.

Moreover, MOTU’s AVB interfaces played nice with all of the host applications I use regularly: Digital Performer, Pro Tools, Studio One, and Sound- Forge Pro. Sound design tools like iZotope Iris 2 and Sony Spectral Layers Pro were just as happy. I found it well worth the time to name inputs and outputs in the MOTU Web app so that they showed up in the DAWs. I saved presets containing names, as well as routing, for tracking (lots of mic inputs), overdubbing (track monitoring as well as mic inputs), and mixing (integrating outboard gear). These presets were very helpful in speeding workflow.



There is an inescapable tradeoff between power and ease of use; the price for increased flexibility is greater complexity. Providing access to more features and options creates the necessity of dealing with them all, and this tradeoff heightens significantly with quantity; lots of channels means lots to handle and go wrong.

This issue manifested in a few areas while I was using the AVB interfaces. The first was the introduction of additional layers of routing in the signal path. I set up the 1248 as the master interface that was connected to the computer. If I plugged a mic into a preamp input on the 8M, getting that signal to a DAW required routing it in the Web app to a channel in an AVB stream from the 8M to the 1248, choosing that stream in the 1248 as an input stream, routing from the correct channel of the correct stream to one of the channels going out to the computer, then, in the DAW, mapping that interface channel to a software input channel and, finally, choosing that input channel as the source for my track. It’s all logical and understandable, but a lot to deal with and keep in your head.

With three interfaces connected, and all of the channels each can handle for input, output, and mixing, the size of the routing matrix itself becomes an issue. MOTU allows sections of the matrix, such as analog inputs or ADAT input channels, to be collapsed, but when a section is collapsed you see only that there is routing happening, but not what the routing is. I developed the habit of leaving any sections I was dealing with in an expanded state, but that put so many connections onscreen, I had to concentrate in order not to route, for instance, channels to the mixer instead of to the computer. The Web app’s GUI does as good a job as I’ve seen in finessing the power-vs.- ease-of-use tradeoff, but it can’t be eliminated.

Then there is the issue of switching the mixer between input sources during recording and playback of channels when reviewing a just-recorded take. You can create presets that remember the state of the entire interface system for each setup you use, which is one way to solve this problem. MOTU provides a collection of presets for common needs, such as using an interface as an input expander, a basic interface, or just using the onboard mixing. I’d love to see MOTU implement a quick way to call up presets from the keyboard for fast context switching.

These devices are feature-packed, and comprehensive documentation is essential to using them. The manual I received covers all three of the AVB interfaces I reviewed, as well as the AVB switch, in less than 100 pages (the index is just over two pages), yet it just wasn’t enough information to get my larger, networked sessions running without a lot of experimentation and searching around. The manual has helpful illustrations and instruction on hooking up common system configurations, and MOTU has posted a series of helpful tutorial videos: Visit the AVB product page at, click the Resources tab, and scroll down to find them. The videos explain routing and other advanced topics but do not give sample applications.

There is one other issue that could be an inconvenience, especially for small studios and systems. Quarter- inch outputs from the MOTU AVB interfaces are balanced but not cross-coupled. There are good audio reasons for doing this, but it means that you cannot simply plug a regular, unbalanced TS plug into an output jack without risking distortion. (You would have to use a TRS plug with the ring contact disconnected, in that case.) In an installation where connections will remain as they were made, you wire it right the first time and you’re done. But if you want to be able to patch out to unbalanced gear freely, you must have properly wired custom adapters or cables available.



I worked these interfaces pretty hard, using lots of channels, various sources and microphone types, and performing tracking, overdubbing, mixing, and rehearsal sessions with them. I made presets and patched in outboard compressors and reverbs. What I found was excellent audio performance and awesome capabilities and flexibility.

If you move into bigger, more complex networking situations, however, expect a significant learning curve. But once I finally got my head around signal flow and reconfiguration of the system, I had few functional complaints. I’d love to see MOTU incorporate color-coding in key places (like the routing matrix) and add a few other features to help tame the complexity of all that I/O distributed across multiple interfaces, but the challenge of complexity is inherent, not poor design. More documentation would make a difference.

The MOTU AVB family of interfaces provides excellent solutions for a wide variety of contexts— small studios, venue installations, multiroom production facilities, even live sound. The ability to configure a system with the I/O you need, scale systems up easily, and use long cable runs is very powerful. Running the control software as a Web app is an elegant solution to cross-platform control. The onboard mixing is easy to use.

I found a whole lot to like about the MOTU AVB interfaces and hardly anything not to like. Highly recommended.

Powerful, comprehensive, and extremely flexible system. Excellent audio quality. Scales easily from a one-room studio to a multi-venue complex.

Needs more documentation and tutorial materials.

1248 $1,495 street 16A $1,495 street 8M $1,495 street AVB Switch $295 street

Larry the O has been involved with audio and music for more than 35 years as a performer, engineer, sound designer, producer, composer, and writer. He has written many dozens of articles for Electronic Musician since 1986.


The 411 on AVB

AVB is an extension to the Ethernet standard designed to provide reliable, low-latency audio and video performance using basic Ethernet hardware. It is an open standard, which has the advantage of not costing manufacturers any kind of license fee to use it, but the disadvantages that development tends to be slower than with a proprietary standard (because numerous companies must agree on changes; always difficult to achieve) and implementation details can vary.

By contrast, proprietary systems such as Audinate’s Dante (also based on Ethernet hardware) can be developed by their creators as they wish, and the developer can exert a modicum of control over implementations. The disadvantage is that equipment manufacturers must pay license fees to use the system, adding to the cost.

The primary aspect of AVB that optimizes it for use with real-time audio and video is, bandwidth is reserved for each audio or video stream to ensure samples reach their intended destinations on time. Audio samples running over standard Ethernet are not guaranteed to arrive on time (or, in some cases, at all), latency is not entirely predictable, and there is no reliable means of providing synchronization and clocking. AVB is designed to remedy all of this. It carries a master clock signal and even allows query and discovery of devices on the network.

MOTU says that its 1Gbit AVB network can carry up to 512 channels over the network. Channels can be moved not only from interfaces to a host computer, but between interfaces. The use of three or more devices requires the addition of an AVB-compliant switch.

Another major plus of Ethernet-based systems like AVB is that devices can be placed up to 100 meters apart. For a musician, that means you can put an interface in your house, run one skinny cable from the house to the studio out back, and be able to record vocals in the bathroom and the piano that sits in the living room while the drummer and guitar amps are recorded in the studio with an interface that lives there. In live performance, an AVB interface with lots of mic preamps makes a great stage box, while another interface at front-of-house with line inputs (or even digital I/O) carries prerecorded material, outboard synthesizers, or effects. Of course, in installations and commercial production facilities, interfaces can be located in different venues or studios.