Swissonic USB Studio D

Fancy doing some hard disk recording on your computer without using a soundcard? Martin Walker looks at an intriguing combination of mixer and USB interface that could let you do just that.

Now that so many software packages provide multitrack digital audio recording facilities, along with real‑time effects and comprehensive mastering options, it's hardly surprising that so much music‑making happens inside the computer, rather than outside it. The main problem for those with existing equipment such as mics, guitars, synths, and so on, is how to connect this equipment to the computer for recording purposes, so that its signals can also benefit from all the facilities offered by software.

One answer might be to buy a small desktop mixer with some decent mic preamps and basic mixing facilities. However, if your computer is stuffed full of software EQ and effect plug‑ins, many of the typical features of such small mixers (such as multi‑band EQ and multiple auxiliary sends) may be redundant. Swissonic (formerly MusicNet) have come up with a novel solution, consisting of a 1U rackmounting mixer with inputs for two mics and two guitars, a phono connection (for a record deck), four stereo inputs for synths and the like, and a USB interface.

This last feature lets you transfer any combination of signals from the mixer to any computer equipped with a USB port, and store them on its hard drive using your favourite audio software. You can also replay the audio files stored on your hard drive back through the USB link and monitor them through the mixer's output, or run a multitrack audio sequencer and monitor its final stereo mixdown signal in the same way. Theoretically, these facilities mean that you could dispense with a soundcard altogether! It's certainly a novel approach, and since all the analogue signals remain in the rack unit, audio quality should also be extremely high.

Swissonic have called their product the USB Studio, and it comes in two versions: the standard USB Studio and the slightly more expensive USB Studio D under review here. For the extra money Swissonic add co‑axial and optical digital ins and outs to interface with other digital equipment such as a DAT recorder.

Facilities Overview

The USB Studio D is built into a steel rackmount case with an internal mains power supply and 115/230 Volt selector switch, along with a combined IEC mains socket and fuse holder. It's quite a heavy package, largely because of the internal mains transformer, and it certainly looks built to last.

The mixer has 11 inputs in total — two mic, two instrument, one line/phono, four stereo, a digital in, and a Computer input — and two output buses (monitor and record). Each of the inputs has a rotary gain control on the front panel, and all but one of them also have latching record‑enable buttons. (The one that doesn't is the Computer input to which the USB audio signal returns.) When any record‑enable button is pushed in, the associated input signal is routed to the mixer record bus. If the button is left in the out position, the signal goes instead to the mixer monitor bus. Both bus signals are available from rear‑panel sockets, and the record bus is also available inside a computer via the USB interface. The supplied manual is well written and explains each input and output in great detail, but the addition of a signal flow chart (like those provided with most mixers) showing how the inputs and outputs can be interconnected would save a lot of initial head‑scratching.

As you might expect from such a comprehensive array of inputs and outputs, the USB Studio D is bristling with knobs and sockets, knobs being on the front panel and sockets at the back, with the exception of the headphone output.

A Tour Of The Inputs

Each mic input is equipped with a balanced XLR connector, 48V phantom power, and a latching phase‑invert button to help solve phasing problems when using multiple microphones. There's also an insert point for external processing, such as compression or EQ.

Mic input 1 is routed to the left‑hand channel in the USB stereo signal, while input 2 is routed to the right. This certainly helps if you want to record in stereo, and also when recording two mono signals. However, both mic input signals are sent to both channels on the monitor bus, and therefore appear more usefully in the middle of the stereo image when mixing. The mic preamp circuitry provides up to 50dB of gain and is claimed to be "one of the finest ultra‑low‑noise amplifier designs available."

The two instrument inputs have a similar gain range to the mic inputs but have unbalanced quarter‑inch jack connectors and an extremely high input impedance of 20MΩ. This makes them suitable either for piezo mics or for magnetic guitar pickups. They are again hard‑wired to left and right channels respectively, to keep the signals isolated from each other when recording, but are centrally panned when being monitored.

The next input is stereo, on two phono sockets, and can do one of two jobs: a latching button on the rear panel switches it between line and phono mode. In the phono position it provides 34dB of gain and RIAA equalisation for the direct connection of a record deck, while in the line position it becomes a unity‑gain input with a 50kΩ input impedance (suitable for many devices, such as cassette decks or DAT recorders). An additional 4mm banana socket is provided as a suitable earth point for a record deck.

Four stereo line‑level inputs suitable for keyboards or MIDI modules come next. Sadly, providing stereo quarter‑inch jack sockets on the rear panel won't make connections very easy for most musicians, who will nearly all need to make up special leads ending in a stereo jack plug [or buy a ready‑made long insert lead and use it 'back to front' — Sub‑Ed]. This is especially frustrating given that the rear panel has enough space to fit twin mono jack sockets (one above the other). Even twin phono sockets might be more popular than the current arrangement.

The next input is the digital in, which lets you mix in a signal from either the Toslink optical or phono co‑axial S/PDIF digital connectors on the back panel. Only one of these at a time can be active, so there's an associated button for selecting between them. Since the digital signal is passed through the D‑A converter before reaching the mix buses, the digital input also has a variable level control, and a lock indicator beneath this shows when a valid digital signal is being received.

The final 'Computer' input simply has a knob on the front panel (there is no input socket on the rear panel) to adjust the level of the USB signal coming back from the computer, and is permanently connected to the monitor bus.

Overall, this is a useful and comprehensive selection of inputs, but the 11 uniformly spaced level controls on the front panel are hard to distinguish between, since they're only differentiated by small labels.

Outputs

The record bus signal is available from a stereo pair of rear‑panel Rec Out phono sockets. The bus is also connected to the rotary Rec Level control on the front panel, and the output level is measured by a pair of peak‑reading, 8‑segment LED meter displays. The meters have an overall range of 26dB, the top LED illuminating at 1dB below clipping. All my PC applications, however, showed levels to be about 4dB lower than the meter equivalent.

The USB Studio D provides a comprehensive range of analogue and digital I/O for your computer without taking up a PCI slot.

A further stereo pair of Line Out phono sockets on the rear panel carries the monitor bus signal, while a third pair, labelled Mon Out, is wired after the front‑panel Monitor level control and associated Mute button. The full monitor bus signal is also available to the headphone output.

The Digital Out control sets the level of signal that is sent to both digital outputs from either the record or monitor bus. There's an associated LED digital overload indicator directly beneath the knob, and two latching buttons: one to set the sample rate (44.1kHz or 48kHz) and one to select whether the signal is taken from the record or monitor bus.

Also on the front panel are a power switch and a cluster of three LEDs — a green power indicator LED, and two red LEDs to indicate record overload and monitor overload (each lights at 6dB below clipping). On the rear panel the one remaining item is the USB socket. A two‑metre USB‑to‑USB lead is supplied, which should be long enough for most purposes.

Mixing

When I started using the Studio D I noticed how good and quiet the mic inputs sounded, and as I worked my way through the other types of input I was impressed by their audio quality too. To minimise background noise the individual level controls should be turned up until the overload LED for the appropriate bus (monitor or record) just flashes briefly on peaks. This ensures that signal levels are within 6dB of clipping.

When recording, setting any record‑enable switch to the 'on' position normally removes its input signal from the monitor bus, but you can still monitor it using the Computer level control as it returns from the USB bus. However, considerable latency will be experienced with this method. (USB devices don't have ASIO drivers, and on my PC system I only managed to drop the MME latency value to 186mS inside Cubase VST). Fortunately, Swissonic have provided a 'zero' hardware latency solution: if you remove the top cover of the mixer each input channel has a movable link on the circuit board that gives the option of leaving the input signal on the monitor bus, even when the channel is switched to record enable.

Overall, the audio mixing facilities of the USB Studio D are fairly comprehensive and of high audio quality, but I do think that Swissonic have made a mistake in using black knobs and buttons along with a black front panel. While you can gain an overview of most mixing desks from several feet away, in my studio I could scarcely see many of the Studio D controls at this distance, let alone their positions! The rotary knobs do have bright blue pointers, but there are no markings around them to help users achieve repeatable settings, and it is almost impossible to see whether the record‑enable buttons are in or out in average studio lighting conditions, unless you look down on the unit from above.

Computer Interfacing

These are the controls that appear for the new 'Desktop Speaker' device in the playback section of the Windows Volume Control utility, and their recommended positions. There are no recording level controls.Since the USB Studio D is a standard USB peripheral it doesn't need any extra drivers, and should be recognised immediately upon powering up, when plugged into any computer equipped with a USB socket. This includes PCs running Windows 98 and Windows 95 versions OSR2.1 and OSR2.5, and Macs running MacOS 9.0 and 9.1. For playback only, MacOS 9.0 is fine, but 9.1 (or Apple's bug fix for 9.0, downloadable from www.apple.com) is needed to enable USB recording.

When I connected the mixer to my Pentium II 450MHz PC, the new USB device was detected within a few seconds, and after my Windows 98SE CD‑ROM had been requested to install a few standard driver files I was in business. A new 'USB Audio' device showed up in my list of Multimedia devices, along with a new mixer device in the Volume Control menu.

The USB Studio D is cleverly designed, and I've no doubt that some musicians will think it the device of their dreams.

Audio quality when playing back digital audio files via USB was generally excellent, and although the Crystal converters of my benchmark Echo Gina card were slightly clearer at the top end, the difference was subtle. This proved hardly surprising, since when I whipped off the top cover I discovered that the converters used are Crystal CS4222 devices (as used in Midiman's successful Dman2044), and very similar to those used by the Echo range.

However, just as with Opcode's DATport, which I reviewed in SOS July '99, I did experience a few very low‑level glitches on playback. These were extremely quiet, and I very much doubt that most people would even notice them in normal use (I played back a continuous 10kHz sinewave tone to highlight any tiny problems). Also, I'm fairly sure that this is not due to the design of the USB Studio D, since many other DATport users did not experience these problems, but it still leaves me with lingering doubts over the performance of USB digital audio in general with some computers.

Nevertheless, all my USB Studio D recordings were faultless, and according to my tests with Wavelab can be made at either 16‑bit or 20‑bit resolution, though USB playback is only available at 16‑bit. RMS background noise measured 91dB. The converters on the Studio D digital I/O sockets are completely separate from those of the USB interface, so you can connect a digital input running at one sample rate and record it via USB at another, for high‑quality real‑time sample‑rate conversion. The only down side of this design approach is that you don't get bit‑for‑bit transfers, since the digital signals are converted to analogue, mixed on the record or monitor buses, and then converted back to digital again via the USB converters.

I know of no other device with similar facilities. For those without a spare expansion slot for a soundcard, or using a sealed system such as a laptop, it's potentially an ideal solution.

Final Thoughts

The USB Studio D is cleverly designed, and I've no doubt that some musicians will think it the device of their dreams. Others may be concerned about access to the rear‑panel sockets once the mixer is bolted into a rack but, to be fair, with this number of inputs there simply isn't enough space to fit sockets at the front. A few ergonomic tweaks would make the USB Studio simpler to use, but I know of no other device with similar facilities. For those without a spare expansion slot for a soundcard, or using a sealed system such as a laptop, it's potentially an ideal solution.

In fact, given that the cheapest USB digital audio interfaces start at about £200, if you choose the USB Studio D you're only paying another £280 for the mixer component, and a further £50 for the extra digital I/O. If you have a USB socket on your computer — and you will if you're the owner of an iMac, a recent G3/G4 Mac, or one of many PCs built in the last couple of years — but no provision for adding a soundcard, the USB Studio D looks eminently suitable and is good value for money.