A digital I/O device that doesn't make you play card games.Now that the Universal Serial Bus (USB) is standard equipment on PCs and Macs, the race is

A digital I/O device that doesn't make you play card games.

Now that the Universal Serial Bus (USB) is standard equipment on PCs and Macs, the race is on to exploit this versatile I/O channel. One innovative design is the Swissonic USB Studio/D, a 1U rack-mount mixer and digital interface that mixes audio signals from several types of analog inputs, converts them to digital format, and sends the data (in stereo) to the host computer over its USB cable. The Studio/D also accepts stereo digital audio from the computer or from its S/PDIF jacks and converts the data to an analog signal.

To route its wide variety of audio sources, the Studio/D incorporates two buses: monitor and record. Any of the audio inputs can be routed to either of the two buses, but the default input routing is to the monitor bus. The monitor bus signal is fed to the monitor line outputs as well as to the headphone jack, and the record bus signal is converted to digital format and then fed to the computer through the USB connection.

Of course, the Studio/D does much more than this simplified description implies. Thanks to its USB interface and some wise design choices, it offers several unique capabilities.

SET ME UPThe Studio/D is a sleek-looking device in a sturdy black steel case (see Fig. 1). Its front-panel, rocker-type power switch is conveniently located on the far right; the 15 rubberized knobs provide a weighty, confidence-inspiring feel with nice tactile feedback. The rather small buttons between the knobs, however, are difficult to operate because they don't protrude far enough from the front panel, and the panel labels are so tiny that they're difficult to read.

Initial setup was a breeze. With my PC already up and running Windows 98, I connected the Studio/D to the computer's USB port with the provided USB cable and switched on the unit. Within a couple of seconds, Windows detected the device and started to load the USB drivers needed to support it. (I keep the install files for Windows on my hard drive, which makes updating and reloading system files a snap.) Once the process was complete, new audio input and output drivers were available and ready to use. Installation was a joy compared with the configuration nightmares I've had with other products.

For my initial test of the Studio/D, I played a WAV file through the unit and experienced badly stuttering playback. I checked my BIOS settings and turned on Ultra DMA hard drive transfers. The situation improved, but the stuttering did not disappear completely. A quick check with Swissonic confirmed that the revamped USB drivers included with Windows 98 Second Edition are required to support streaming audio over USB, a fact not specified in the user manual. I updated the drivers using the Windows 98 service pack (available for free on Microsoft's Web site), and the stuttering stopped.

The Studio/D is compatible with both Windows and Macintosh USB implementations. ASIO drivers are available for Mac OS 9 and should be available for Windows by the time you read this.

The Studio/D user manual is a rather meager booklet with 14 pages of text, including a 1-page quick-start guide. The documentation for the device, though complete, is not expansive; more advice on how to use the Studio/D in various recording situations would be welcome.

BACK IN BLACKThe Studio/D's back panel (see Fig. 2) provides two balanced XLR microphone jacks with 48V phantom power, which is switched with buttons next to the jacks. When phantom power is engaged, a front-panel LED illuminates. Each mic input is also equipped with a TRS effects-insert jack and a polarity-invert button.

The mic-preamp trim and gain controls are combined into a single level control for each jack. This design keeps the unit compact and simplifies the adjustment of the mic input levels, but comes at the cost of flexibility in the adjustment of the mic-preamp trim levels. If you turn the level control hard left, it acts as a disengage switch, completely cutting the mic signal. No click or other tactile feedback, however, will confirm that this has happened.

When the Studio/D's mic signals are routed to the monitor bus, they are both centered in the monitor mix. When you route them to the record bus, mic 1 is panned hard left and mic 2 is panned hard right. This arrangement limits your flexibility somewhat, but keep in mind that this is a combo device rather than a full-fledged mixer. Some compromises have been made to save front-panel real estate and to reduce the number of controls and switches. With the number of inputs on the Studio/D, there just isn't room for pan pots.

The same panning scheme is employed on the Studio/D's two high-impedance TS mono instrument inputs. As with the mic controls, the preamp trim and gain controls are handled by a single level knob located on the front panel. These inputs are suitable for instruments using piezo or magnetic pickups or for unbalanced microphones.

Next to the mono instrument inputs are two RCA jacks that serve double duty as line-level or phono inputs. (A banana-jack grounding terminal for a turntable is also provided.) A button switches the input between unbalanced line level and phono and engages the RIAA phono preamp.

The preamp's input capacitance can be set to better match your turntable's cartridge, but you have to remove the Studio/D's cover to get at the jumpers that control this adjustment. Unfortunately, no information about how to set the two jumpers is in the manual or on the circuit board itself. (According to Swissonic, the default input capacitance is 40 pF with both jumpers open and 250 pF with the jumpers shorted.)

To the left of the RCA jacks are four unbalanced stereo TRS input jacks, each with its own level control and bus-selection switch.

Next to these jacks are three RCA output pairs for the Studio/D's monitor and record buses. The line-out pair provides the signal from the monitor bus before the main monitor level control. The monitor out pair also takes its signal from the monitor bus, but after the level control and mute switch. The third output pair is fed from the record bus, before the main record level control. The Studio/D's digital I/O section, on the far left of the back panel, has jacks for coaxial and optical S/PDIF (more on this shortly).

The unit's voltage-selection switch allows you to choose between 115V and 230V, and the power connector features an easy-to-access integrated fuse holder. Thankfully, Swissonic put the power supply inside the unit, so you don't have to add an annoying wall wart to your collection.

POTS AND PANSThe Studio/D's front panel is logically laid out with a pair of controls for each input jack: a level knob and a Record Enable button. When the Record Enable button is out, the signal goes to the monitor bus; when it is pushed in, the signal is routed to the record bus.

The stereo channel arriving from the computer over the USB cable is always routed to the monitor bus, and it has a knob (labeled "Computer") for setting its level. The adjacent Rec Level knob sets the level of the stereo channel that is output to the computer over the USB cable. A pair of 8-segment, peak-level LED meters shows the output signal levels; the top LED lights up at 1 dB below clipping.

The overall level of the monitor bus as presented at the monitor outputs is controlled with its own knob, which is thoughtfully accompanied by a mute button. The monitor bus also feeds the headphone jack, which has its own level control.

Some applications can return a stereo audio stream through the USB connection for monitoring. However, your computer may not have enough CPU power to process the return stream with reasonably low latency. If that's the case, you can work around the problem by overriding the switching behavior for any audio input in the Studio/D, so that when you assign an input to the record bus, the signal remains present on the monitor bus as well. Then you can monitor your recording using the analog monitor or headphone outputs. You configure this option with jumpers inside the unit, and it's available for all inputs, both analog and digital. (You can also monitor the record bus directly through its pair of RCA jacks on the back panel.)

The Studio/D's front panel includes several status LEDs. For example, the monitor and record buses each have an overload indicator that lights up when less than 6 dB of headroom are left. And, of course, there is a power-on indicator.

The unit's Record Enable, Monitor Mute, and other switches, however, are small and hard to see. They would benefit greatly from a few more status LEDs, which would provide a better visual indication of their positions. That might have saved me from some frustrating moments when switches weren't set the way I thought they were. Also, a couple of the switches on my sample unit (Monitor Mute and the Phono/Line selector) were noisy, giving loud pops when I used them.

DIGITAL DOMAINThe Studio/D uses an ADC with 20-bit resolution to convert the Record bus signal to digital for transmission to the computer. On the return trip (playback), the DAC converts the signal from the computer with 16-bit resolution. A separate converter in the Studio/D's digital section handles the S/PDIF ports. It offers 20-bit A/D/A resolution and features dynamic range and noise numbers that are slightly superior to those in the USB section.

For getting signals into and out of the digital section, the Studio/D supplies S/PDIF jacks in two formats: RCA (coaxial) and Toslink. A switch next to the jacks lets you select which of the two inputs is used. The digital outputs can be used simultaneously.

A knob on the front panel controls the level going to the S/PDIF outputs; a switch gives you the choice of a 44.1 or 48 kHz sample rate. For added flexibility, you get a second switch for determining whether the monitor or record bus is routed to the digital output. You can even use the Studio/D as a high-quality stand-alone A/D converter without engaging the USB connection at all. To help you keep the signal clean, an overload LED illuminates when the digital output is less than 6 dB below clipping.

The Studio/D controls the digital-input signal level through a dedicated Digital In knob; a Record Enable switch routes the signal to the record bus. Sample conversion is performed automatically if you use different rates in the S/PDIF and USB sections of the Studio/D. When the unit has locked on to a digital input stream, a Lock indicator lights up and the digital-output sample rate is set to match the input. For those who don't need the Studio/D's S/PDIF ports, Swissonic offers the USB Studio ($699), a nearly identical unit that lacks the digital inputs and outputs.

VINYL GROOVESIf you're looking for a simple way to transfer those warm (and sometimes scratchy) sounds from vinyl records to the computer, the Studio/D is a good choice. I did some vinyl-to-digital transfers, and the results were excellent. Any less-than-perfect highs in the source material were rendered faithfully, rather than made grainy or harsh, by the conversion.

The Studio/D also adeptly handled a wide assortment of audio signals. For example, it performed quite well when I plugged an electric guitar directly into one of the instrument inputs, especially when I routed the guitar signal through a SansAmp PSA-1 amp emulator first.

Microphone signals were also handled well. I got very good results when I miked a Fender tube amp with a self-powered condenser mic. The final recording exhibited all the singing highs, guts, and grit that the tube-distorted original did.

I can imagine the Studio/D playing a number of roles in a personal studio. The unit is not only sturdy, but quite portable. Combined with a USB-equipped laptop, it could be used successfully in all sorts of recording situations. Moreover, its wide variety of inputs and freedom from adapter cards make it suitable for a broad range of projects. It could also come in very handy for mixing signals or for serving as a stand-alone A/D converter when a computer isn't available.

Some users might bemoan the unit's lack of panning controls, but its TRS effects inserts, wide variety of ins and outs, and other features go a long way toward offsetting the deficiency.

Overall, Swissonic has delivered a fine digital-I/O unit that is versatile, sonically nonintrusive, and attractively priced. If you're looking for a device that brings digital audio into your computer with a minimum of muss and fuss, the Swissonic USB Studio/D is well worth considering.