M-Audio Duo and Quattro USB Audio Interface Reviews

With the widespread acceptance of USB as the next best thing in convenience and connectivity, it's simple human nature that those people involved in audio

With the widespread acceptance of USB as the next best thing in convenience and connectivity, it's simple human nature that those people involved in audio and music would want to integrate USB audio components into their portable-a-go-go world. In response, M-Audio has introduced two new USB audio interfaces to its line of professional products: the Duo and the Quattro.

Both compact devices are housed in heavy-duty silver metal cases and are powered by 9 VAC wall warts. Each unit includes ¼-inch line-level inputs and outputs that you can independently switch (in I/O pairs) to +4 dBu or -10 dBV levels. The units are shipped with drivers that support ASIO, EASI, MME, and WDM.


The Duo is a 2-in/2-out professional interface that records and plays back a maximum of 24-bit, 96 kHz resolution. In addition to having two line ins and outs, the Duo includes a pair of high-quality mic preamps that sport XLR inputs, switchable phantom power, independent 20 dB pads, and signal/clip LEDs (see Fig. 1).

In the unit's normal mode, the mic preamps or the line-level inputs are automatically routed to the digital-input section. However, by pressing a front-panel Stand Alone Mode button, the Duo also can be used as an independent mic preamp, without the need for a computer. Simply plug in the mics and then plug the box's line-level outputs in to any device input. In that mode, the Duo can also be used as a standalone 24-bit A/D converter by streaming the line or mic inputs through to its S/PDIF outputs at selectable rates of 44.1, 48, 88.2, and 96 kHz. You can also configure the box as a handy standalone headphone-monitor amp; just plug a signal in to the line-ins and monitor through the headphone output. (In normal operating mode, the headphone jack monitors the output signal.)


The Quattro is a 4-in/4-out audio interface that also works at resolutions up to 24 bits and sampling rates up to 96 kHz (see Fig. 2). Because of USB's limitations, the box can deliver only a 4-in/4-out throughput when processing 16-bit audio with 44.1 or 48 kHz sampling rates. It also provides 2-in/4-out or 4-in/2-out processing at 24-bit resolution with the same sampling rates. At the top of the scale, the Quattro offers 2-in or 2-out processing with 24-bit resolution at 88.2 or 96 kHz sampling rates. The Quattro also includes a Direct Monitoring feature that can route inputs 1 and 2 as well as 3 and 4 directly through to their respective outputs, thereby eliminating monitoring latency when recording.

In addition to offering front-panel MIDI In and Out ports, the Quattro includes provisions for an optional 15-pin DB connector that can be used to connect an M-Audio Omni I/O interconnect/mixer box directly to the Quattro's four input and output buses. Plugging in the portable Omni I/O provides access to two mic preamps, a mixing section with eight additional inputs, two headphone sends, an FX send and return, a dedicated monitor and output bus section, and an auxiliary input section.


I started by plugging the Duo in to my brand-spankin'-new Dell Inspiron 8100 laptop running Windows XP. (A lot of people have been buying this laptop for audio applications because of its high display resolution, dual-monitor capabilities, and high-quality onboard audio card.) It's important to follow the Duo manual's simple directions, because the Audio Configuration Manager needs to be loaded for the Duo to work properly, even after XP tells you that the device is loaded and ready for use.

After the necessary software was installed, I started off by playing back several 16-bit, 44.1 kHz sound files using Syntrillium's Cool Edit Pro with the Duo's MME drivers. I quickly encountered loud bursts of digital hash caused by a power-saving feature called Speed Step that is designed into many newer PC laptops. The feature acts like an intelligent gear shift that throttles the CPU speed up and down to save on battery power while meeting current processing demands. Although that's good for most applications, it can get in the way of high-demand USB media devices. After Speed Step was turned off, the loud noises went away and the laptop played back and recorded stereo files without a hitch.

Once the laptop was working, my next step was to use the Duo with my studio desktop computer. The unit worked perfectly, although plugging it in disabled my main audio card, an M-Audio Delta 1010. When I unplugged the Duo's USB cable, the 1010 came back online. That also happened on a second generic PC that was fitted with a simple Sound Blaster card. It turns out that desktop PCs share USB resources with a physical PCI card slot on the motherboard — specifically, slot 3 on Intel-based systems and slot 4 on AMD-based systems. If you lose your audio card when you plug in a high-bandwidth USB device, try moving your sound card to another slot.

You're probably starting to see that USB on the PC isn't always fun and games. However, the problems that you're likely to encounter stem from the PC's design architecture and aren't the fault of either of M-Audio's devices. Reportedly, there are far fewer setup problems when installing such USB devices on a Mac. If you'd like to learn more about optimizing your Windows XP PC for making music, a good place to visit is www.musicxp.net.


I tested both audio interfaces on my laptop with the ASIO driver and Steinberg's Nuendo. The Duo's sound quality was what I've come to expect from M-Audio: superb. The unit worked like a charm with 16-bit, 44.1 kHz and 24-bit, 96 kHz audio. The mic preamps stacked up to the better preamps in my studio; they sounded present yet warm and full-bodied. I love the fact that the Duo can be used as a standalone mic/line preamp and digital audio converter. That feature makes the box an important addition to any on-the-go audio toolbox.

The Quattro's converters are as high in quality as the Duo's, and they worked without a hitch. The Direct Monitor function eliminates any latency that might be introduced by the system or audio editor, and it lets you monitor your input signal at the press of a button. I also discovered that, contrary to popular belief, you can stream more than six audio channels over USB at one time. Simultaneously recording and playing back from all of the Quattro's audio ins and outs at 16-bit, 44.1 kHz worked perfectly.

Speaking of I/O, when the MME (and WDM) driver is chosen from the software Audio Configuration Manager, only two of the Quattro's I/O channels can be accessed, no matter what sampling rate is chosen. In addition, even when you choose the MME driver in the Audio Configuration Manager (for the Duo or the Quattro), the settings always revert to the default ASIO driver when the PC is turned off; the software won't retain its last setting.


All in all, once I configured my laptop, the Duo and the Quattro were top-notch and highly versatile digital audio interfaces. The Duo was a particular favorite for its amazing range of mic-preamp and interface applications. It is indeed a mean little USB mic pre and standalone A/D converter.

David Miles Huberis the author of Modern Recording Techniques (Focal Press, 2001). Learn about the book and find industry-related links and info atwww.modrec.com.

Minimum System Requirements


MAC: USB (native)-equipped G3; 128 MB RAM; OS 9.1

PC: USB-equipped Pentium II/333; 128 MB RAM; Windows 98SE/ME/2000/XP


MAC: USB (native)-equipped G3; 128 MB RAM; OS 9.1; OMS 2.3.8 for MIDI

PC: Pentium III/500; 128 MB RAM; Windows 98SE/ME/2000/XP

Duo Specifications Quattro Specifications

Inputs(2) balanced XLR mic with switched 48V phantom power; (2) unbalanced ¼" line (+4 dBu or -10 dbV)(4) balanced ¼" (+4 dBu or -10 dBV)Outputs(2) balanced ¼" (+4 dBu or -10 dBV); (1) ¼" headphone(4) balanced ¼" (+4 dBu or -10 dBV)Resolution16- and 24-bit16- and 24-bitSampling Rates44.1, 48, 88.2, 96 kHz44.1, 48, 88.2, 96 kHzMIDI I/On/a(1) In, (1) Out Digital I/OS/PDIF coaxial (16-, 20-, and 24-bit output)n/aDynamic Range105 dBA (line in to line out); 107 dBA (mic in to line out)101 dBA (input); 104 dBA (output)Total Harmonic Distortion<0.002%<0.002%Frequency Response22 Hz-22 kHz (+0, -0.3 dB)22 Hz-22 kHz (+0, -0.3 dB)Dimensions8.50" (W) × 1.75" (H) × 5.00" (D)6.00" (W) × 1.75" (H) × 5.00" (D)Weight2.4 lb.1.7 lb.


Duo and Quattro
USB digital audio interfaces
Duo $349.95
Quattro $349.95


PROS: Support rates up to 24-bit, 96 kHz. The Duo can be used as an audio interface or independent mic preamp and A/D converter. The Quattro delivers simultaneous 4-in/4-out audio at 16-bit, 44.1 kHz as well as MIDI I/O.

CONS: When using MME drivers, only two of the Quattro's channels can be used by an audio application.


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